[RFC,v2,8/9] drm: writeback: Add out-fences for writeback connectors

Message ID 1477472108-27222-9-git-send-email-brian.starkey@arm.com (mailing list archive)
State Not Applicable, archived
Headers

Commit Message

Brian Starkey Oct. 26, 2016, 8:55 a.m. UTC
  Add the OUT_FENCE_PTR property to writeback connectors, to enable
userspace to get a fence which will signal once the writeback is
complete.

A timeline is added to drm_connector for use by the writeback
out-fences. It is up to drivers to check for a fence in the
connector_state and signal the it appropriately when their writeback has
finished.

It is not allowed to request an out-fence without a framebuffer attached
to the connector.

Signed-off-by: Brian Starkey <brian.starkey@arm.com>
---
 drivers/gpu/drm/drm_atomic.c        |   60 +++++++++++++++++++++++---
 drivers/gpu/drm/drm_atomic_helper.c |    5 ++-
 drivers/gpu/drm/drm_writeback.c     |   80 +++++++++++++++++++++++++++++++++++
 include/drm/drm_connector.h         |   14 ++++++
 include/drm/drm_writeback.h         |    2 +
 5 files changed, 155 insertions(+), 6 deletions(-)
  

Comments

Daniel Vetter Oct. 26, 2016, 11:09 a.m. UTC | #1
On Wed, Oct 26, 2016 at 09:55:07AM +0100, Brian Starkey wrote:
> Add the OUT_FENCE_PTR property to writeback connectors, to enable
> userspace to get a fence which will signal once the writeback is
> complete.
> 
> A timeline is added to drm_connector for use by the writeback
> out-fences. It is up to drivers to check for a fence in the
> connector_state and signal the it appropriately when their writeback has
> finished.
> 
> It is not allowed to request an out-fence without a framebuffer attached
> to the connector.
> 
> Signed-off-by: Brian Starkey <brian.starkey@arm.com>

Ah, here it is, so much for reading patches strictly in-order ;-) One
small comment below, otherwise I think this looks good. Again review from
Gustavo for the out fences stuff would be really good (so pls cc him). And
I think some igt testcases to exercise all the corner-cases in here.

> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index a5e3778..7d40537 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -199,6 +199,7 @@ int drm_display_info_set_bus_formats(struct drm_display_info *info,
>   * @best_encoder: can be used by helpers and drivers to select the encoder
>   * @state: backpointer to global drm_atomic_state
>   * @fb: Writeback framebuffer, for DRM_MODE_CONNECTOR_WRITEBACK
> + * @out_fence: Fence which will clear when the framebuffer write has finished
>   */
>  struct drm_connector_state {
>  	struct drm_connector *connector;
> @@ -216,6 +217,9 @@ struct drm_connector_state {
>  	struct drm_atomic_state *state;
>  
>  	struct drm_framebuffer *fb;  /* do not write directly, use drm_atomic_set_fb_for_connector() */

btw if you feel like adding a 2nd comment in-line like above, then that's
a clear signal that you should move your kerneldoc struct member comments
to the inline style. You can freely mix&match inline with top-level struct
member documentation, so no need to change them all. You also missed the
doc for out_fence_ptr, 0day won't like that.

> +
> +	struct fence *out_fence;
> +	u64 __user *out_fence_ptr;

writeback_ prefix for both imo, like in patch 1.

>  };
>  
>  /**
> @@ -546,6 +550,10 @@ struct drm_cmdline_mode {
>   * @tile_v_loc: vertical location of this tile
>   * @tile_h_size: horizontal size of this tile.
>   * @tile_v_size: vertical size of this tile.
> + * @fence_context: context for fence signalling
> + * @fence_lock: fence lock for the fence context
> + * @fence_seqno: seqno variable to create fences
> + * @timeline_name: fence timeline name
>   *
>   * Each connector may be connected to one or more CRTCs, or may be clonable by
>   * another connector if they can share a CRTC.  Each connector also has a specific
> @@ -694,6 +702,12 @@ struct drm_connector {
>  	uint8_t num_h_tile, num_v_tile;
>  	uint8_t tile_h_loc, tile_v_loc;
>  	uint16_t tile_h_size, tile_v_size;
> +
> +	/* fence timelines info for DRM out-fences */
> +	unsigned int fence_context;
> +	spinlock_t fence_lock;
> +	unsigned long fence_seqno;
> +	char timeline_name[32];

Should all have writeout_ prefix. And at that point I wonder a bit whether
we shouldn't just go ahead and create a struct drm_writeout_connector, to
keep this stuff nicely separate. Only change visible to drivers would be
the type of drm_writeback_connector_init, and they'd need to
allocate/embedd a different struct. Worth it imo.
-Daniel

>  };
>  
>  #define obj_to_connector(x) container_of(x, struct drm_connector, base)
> diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h
> index afdc2742..01f33bc 100644
> --- a/include/drm/drm_writeback.h
> +++ b/include/drm/drm_writeback.h
> @@ -16,4 +16,6 @@ int drm_writeback_connector_init(struct drm_device *dev,
>  				 const struct drm_connector_funcs *funcs,
>  				 u32 *formats, int n_formats);
>  
> +struct fence *drm_writeback_get_out_fence(struct drm_connector *connector,
> +					  struct drm_connector_state *conn_state);
>  #endif
> -- 
> 1.7.9.5
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
  
Brian Starkey Oct. 26, 2016, 12:46 p.m. UTC | #2
Hi Gustavo,

It would be great if you could cast your eye over this one as-well.
My intention was to be as similar to the CRTC out-fences as possible.

Thanks,
Brian

On Wed, Oct 26, 2016 at 09:55:07AM +0100, Brian Starkey wrote:
>Add the OUT_FENCE_PTR property to writeback connectors, to enable
>userspace to get a fence which will signal once the writeback is
>complete.
>
>A timeline is added to drm_connector for use by the writeback
>out-fences. It is up to drivers to check for a fence in the
>connector_state and signal the it appropriately when their writeback has
>finished.
>
>It is not allowed to request an out-fence without a framebuffer attached
>to the connector.
>
>Signed-off-by: Brian Starkey <brian.starkey@arm.com>
>---
> drivers/gpu/drm/drm_atomic.c        |   60 +++++++++++++++++++++++---
> drivers/gpu/drm/drm_atomic_helper.c |    5 ++-
> drivers/gpu/drm/drm_writeback.c     |   80 +++++++++++++++++++++++++++++++++++
> include/drm/drm_connector.h         |   14 ++++++
> include/drm/drm_writeback.h         |    2 +
> 5 files changed, 155 insertions(+), 6 deletions(-)
>
>diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
>index 3f8fc97..061ea13 100644
>--- a/drivers/gpu/drm/drm_atomic.c
>+++ b/drivers/gpu/drm/drm_atomic.c
>@@ -30,6 +30,7 @@
> #include <drm/drm_atomic.h>
> #include <drm/drm_mode.h>
> #include <drm/drm_plane_helper.h>
>+#include <drm/drm_writeback.h>
> #include <linux/sync_file.h>
>
> #include "drm_crtc_internal.h"
>@@ -646,6 +647,12 @@ static int drm_atomic_connector_check(struct drm_connector *connector,
> 		return -EINVAL;
> 	}
>
>+	if (state->out_fence && !state->fb) {
>+		DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] requesting out-fence without framebuffer\n",
>+				 connector->base.id, connector->name);
>+		return -EINVAL;
>+	}
>+
> 	return 0;
> }
>
>@@ -1047,6 +1054,8 @@ int drm_atomic_connector_set_property(struct drm_connector *connector,
> 		drm_atomic_set_fb_for_connector(state, fb);
> 		if (fb)
> 			drm_framebuffer_unreference(fb);
>+	} else if (property == config->prop_out_fence_ptr) {
>+		state->out_fence_ptr = u64_to_user_ptr(val);
> 	} else if (connector->funcs->atomic_set_property) {
> 		return connector->funcs->atomic_set_property(connector,
> 				state, property, val);
>@@ -1088,6 +1097,8 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
> 	} else if (property == config->writeback_fb_id_property) {
> 		/* Writeback framebuffer is one-shot, write and forget */
> 		*val = 0;
>+	} else if (property == config->prop_out_fence_ptr) {
>+		*val = 0;
> 	} else if (connector->funcs->atomic_get_property) {
> 		return connector->funcs->atomic_get_property(connector,
> 				state, property, val);
>@@ -1736,6 +1747,39 @@ static int setup_out_fence(struct drm_out_fence_state *fence_state,
> 	return 0;
> }
>
>+static int setup_connector_out_fences(struct drm_atomic_state *state,
>+				      struct drm_out_fence_state *fence_state,
>+				      int *fence_idx)
>+{
>+	struct drm_connector *conn;
>+	struct drm_connector_state *conn_state;
>+	int i, ret;
>+
>+	for_each_connector_in_state(state, conn, conn_state, i) {
>+		struct fence *fence;
>+
>+		if (!conn_state->out_fence_ptr)
>+			continue;
>+
>+		fence = drm_writeback_get_out_fence(conn, conn_state);
>+		if (!fence)
>+			return -ENOMEM;
>+
>+		ret = setup_out_fence(&fence_state[(*fence_idx)++],
>+				      conn_state->out_fence_ptr,
>+				      fence);
>+		if (ret) {
>+			fence_put(fence);
>+			return ret;
>+		}
>+
>+		/* One-time usage only */
>+		conn_state->out_fence_ptr = NULL;
>+	}
>+
>+	return 0;
>+}
>+
> int drm_mode_atomic_ioctl(struct drm_device *dev,
> 			  void *data, struct drm_file *file_priv)
> {
>@@ -1868,8 +1912,8 @@ retry:
> 		drm_mode_object_unreference(obj);
> 	}
>
>-	fence_state = kcalloc(dev->mode_config.num_crtc, sizeof(*fence_state),
>-			      GFP_KERNEL);
>+	fence_state = kcalloc(dev->mode_config.num_crtc + state->num_connector,
>+			      sizeof(*fence_state), GFP_KERNEL);
> 	if (!fence_state) {
> 		ret = -ENOMEM;
> 		goto out;
>@@ -1929,10 +1973,16 @@ retry:
> 		 * Below we call drm_atomic_state_free for it.
> 		 */
> 		ret = drm_atomic_check_only(state);
>-	} else if (arg->flags & DRM_MODE_ATOMIC_NONBLOCK) {
>-		ret = drm_atomic_nonblocking_commit(state);
> 	} else {
>-		ret = drm_atomic_commit(state);
>+		ret = setup_connector_out_fences(state, fence_state,
>+						 &fence_idx);
>+		if (ret)
>+			goto out;
>+
>+		if (arg->flags & DRM_MODE_ATOMIC_NONBLOCK)
>+			ret = drm_atomic_nonblocking_commit(state);
>+		else
>+			ret = drm_atomic_commit(state);
> 	}
>
> 	if (!ret)
>diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
>index bba8672..88da299 100644
>--- a/drivers/gpu/drm/drm_atomic_helper.c
>+++ b/drivers/gpu/drm/drm_atomic_helper.c
>@@ -3234,8 +3234,9 @@ __drm_atomic_helper_connector_duplicate_state(struct drm_connector *connector,
> 	if (state->crtc)
> 		drm_connector_reference(connector);
>
>-	/* Don't copy over framebuffers, they are used only once */
>+	/* Don't copy over framebuffers or fences, they are used only once */
> 	state->fb = NULL;
>+	state->out_fence = NULL;
> }
> EXPORT_SYMBOL(__drm_atomic_helper_connector_duplicate_state);
>
>@@ -3365,6 +3366,8 @@ __drm_atomic_helper_connector_destroy_state(struct drm_connector_state *state)
> 		drm_connector_unreference(state->connector);
> 	if (state->fb)
> 		drm_framebuffer_unreference(state->fb);
>+
>+	fence_put(state->out_fence);
> }
> EXPORT_SYMBOL(__drm_atomic_helper_connector_destroy_state);
>
>diff --git a/drivers/gpu/drm/drm_writeback.c b/drivers/gpu/drm/drm_writeback.c
>index 5a6e0ad..4a6ef30 100644
>--- a/drivers/gpu/drm/drm_writeback.c
>+++ b/drivers/gpu/drm/drm_writeback.c
>@@ -11,6 +11,7 @@
> #include <drm/drm_crtc.h>
> #include <drm/drm_property.h>
> #include <drm/drmP.h>
>+#include <linux/fence.h>
>
> /**
>  * DOC: overview
>@@ -32,6 +33,16 @@
>  * explicitly cleared in order to make a subsequent commit which doesn't use
>  * writeback.
>  *
>+ * Unlike with planes, when a writeback framebuffer is removed by userspace DRM
>+ * makes no attempt to remove it from active use by the connector. This is
>+ * because no method is provided to abort a writeback operation, and in any
>+ * case making a new commit whilst a writeback is ongoing is undefined (see
>+ * OUT_FENCE_PTR below). As soon as the current writeback is finished, the
>+ * framebuffer will automatically no longer be in active use. As it will also
>+ * have already been removed from the framebuffer list, there will be no way for
>+ * any userspace application to retrieve a reference to it in the intervening
>+ * period.
>+ *
>  * Writeback connectors have several additional properties, which userspace
>  * can use to query and control them:
>  *
>@@ -52,8 +63,48 @@
>  *  "PIXEL_FORMATS_SIZE":
>  *	Immutable unsigned range property storing the number of entries in the
>  *	PIXEL_FORMATS array.
>+ *
>+ *  "OUT_FENCE_PTR":
>+ *	Userspace can provide the address of a 64-bit integer in this property,
>+ *	which will be filled with a sync_file file descriptor by the kernel.
>+ *	The sync_file will signal when the associated writeback has finished.
>+ *	Userspace should wait for this fence to signal before making another
>+ *	commit affecting any of the same CRTCs, Planes or Connectors.
>+ *	**Failure to do so will result in undefined behaviour.**
>+ *	For this reason it is strongly recommended that all userspace
>+ *	applications making use of writeback connectors *always* retrieve an
>+ *	out-fence for the commit and use it appropriately.
>+ *	From userspace, this property will always read as zero.
>  */
>
>+#define fence_to_connector(x) container_of(x->lock, struct drm_connector, fence_lock)
>+
>+static const char *drm_writeback_fence_get_driver_name(struct fence *fence)
>+{
>+	struct drm_connector *connector = fence_to_connector(fence);
>+
>+	return connector->dev->driver->name;
>+}
>+
>+static const char *drm_writeback_fence_get_timeline_name(struct fence *fence)
>+{
>+	struct drm_connector *connector = fence_to_connector(fence);
>+
>+	return connector->timeline_name;
>+}
>+
>+static bool drm_writeback_fence_enable_signaling(struct fence *fence)
>+{
>+	return true;
>+}
>+
>+static const struct fence_ops drm_writeback_fence_ops = {
>+	.get_driver_name = drm_writeback_fence_get_driver_name,
>+	.get_timeline_name = drm_writeback_fence_get_timeline_name,
>+	.enable_signaling = drm_writeback_fence_enable_signaling,
>+	.wait = fence_default_wait,
>+};
>+
> /**
>  * create_writeback_properties - Create writeback connector-specific properties
>  * @dev: DRM device
>@@ -136,6 +187,14 @@ int drm_writeback_connector_init(struct drm_device *dev,
> 	if (ret)
> 		goto fail;
>
>+	connector->fence_context = fence_context_alloc(1);
>+	spin_lock_init(&connector->fence_lock);
>+	snprintf(connector->timeline_name, sizeof(connector->timeline_name),
>+		 "CONNECTOR:%d", connector->base.id);
>+
>+	drm_object_attach_property(&connector->base,
>+				   config->prop_out_fence_ptr, 0);
>+
> 	drm_object_attach_property(&connector->base,
> 				   config->writeback_fb_id_property, 0);
>
>@@ -155,3 +214,24 @@ fail:
> 	return ret;
> }
> EXPORT_SYMBOL(drm_writeback_connector_init);
>+
>+struct fence *drm_writeback_get_out_fence(struct drm_connector *connector,
>+					  struct drm_connector_state *conn_state)
>+{
>+	struct fence *fence;
>+
>+	if (WARN_ON(connector->connector_type != DRM_MODE_CONNECTOR_WRITEBACK))
>+		return NULL;
>+
>+	fence = kzalloc(sizeof(*fence), GFP_KERNEL);
>+	if (!fence)
>+		return NULL;
>+
>+	fence_init(fence, &drm_writeback_fence_ops, &connector->fence_lock,
>+		   connector->fence_context, ++connector->fence_seqno);
>+
>+	conn_state->out_fence = fence_get(fence);
>+
>+	return fence;
>+}
>+EXPORT_SYMBOL(drm_writeback_get_out_fence);
>diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
>index a5e3778..7d40537 100644
>--- a/include/drm/drm_connector.h
>+++ b/include/drm/drm_connector.h
>@@ -199,6 +199,7 @@ int drm_display_info_set_bus_formats(struct drm_display_info *info,
>  * @best_encoder: can be used by helpers and drivers to select the encoder
>  * @state: backpointer to global drm_atomic_state
>  * @fb: Writeback framebuffer, for DRM_MODE_CONNECTOR_WRITEBACK
>+ * @out_fence: Fence which will clear when the framebuffer write has finished
>  */
> struct drm_connector_state {
> 	struct drm_connector *connector;
>@@ -216,6 +217,9 @@ struct drm_connector_state {
> 	struct drm_atomic_state *state;
>
> 	struct drm_framebuffer *fb;  /* do not write directly, use drm_atomic_set_fb_for_connector() */
>+
>+	struct fence *out_fence;
>+	u64 __user *out_fence_ptr;
> };
>
> /**
>@@ -546,6 +550,10 @@ struct drm_cmdline_mode {
>  * @tile_v_loc: vertical location of this tile
>  * @tile_h_size: horizontal size of this tile.
>  * @tile_v_size: vertical size of this tile.
>+ * @fence_context: context for fence signalling
>+ * @fence_lock: fence lock for the fence context
>+ * @fence_seqno: seqno variable to create fences
>+ * @timeline_name: fence timeline name
>  *
>  * Each connector may be connected to one or more CRTCs, or may be clonable by
>  * another connector if they can share a CRTC.  Each connector also has a specific
>@@ -694,6 +702,12 @@ struct drm_connector {
> 	uint8_t num_h_tile, num_v_tile;
> 	uint8_t tile_h_loc, tile_v_loc;
> 	uint16_t tile_h_size, tile_v_size;
>+
>+	/* fence timelines info for DRM out-fences */
>+	unsigned int fence_context;
>+	spinlock_t fence_lock;
>+	unsigned long fence_seqno;
>+	char timeline_name[32];
> };
>
> #define obj_to_connector(x) container_of(x, struct drm_connector, base)
>diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h
>index afdc2742..01f33bc 100644
>--- a/include/drm/drm_writeback.h
>+++ b/include/drm/drm_writeback.h
>@@ -16,4 +16,6 @@ int drm_writeback_connector_init(struct drm_device *dev,
> 				 const struct drm_connector_funcs *funcs,
> 				 u32 *formats, int n_formats);
>
>+struct fence *drm_writeback_get_out_fence(struct drm_connector *connector,
>+					  struct drm_connector_state *conn_state);
> #endif
>-- 
>1.7.9.5
>
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Gustavo F. Padovan Oct. 26, 2016, 9:40 p.m. UTC | #3
2016-10-26 Brian Starkey <brian.starkey@arm.com>:

> Add the OUT_FENCE_PTR property to writeback connectors, to enable
> userspace to get a fence which will signal once the writeback is
> complete.
> 
> A timeline is added to drm_connector for use by the writeback
> out-fences. It is up to drivers to check for a fence in the
> connector_state and signal the it appropriately when their writeback has
> finished.
> 
> It is not allowed to request an out-fence without a framebuffer attached
> to the connector.
> 
> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
> ---
>  drivers/gpu/drm/drm_atomic.c        |   60 +++++++++++++++++++++++---
>  drivers/gpu/drm/drm_atomic_helper.c |    5 ++-
>  drivers/gpu/drm/drm_writeback.c     |   80 +++++++++++++++++++++++++++++++++++
>  include/drm/drm_connector.h         |   14 ++++++
>  include/drm/drm_writeback.h         |    2 +
>  5 files changed, 155 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 3f8fc97..061ea13 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -30,6 +30,7 @@
>  #include <drm/drm_atomic.h>
>  #include <drm/drm_mode.h>
>  #include <drm/drm_plane_helper.h>
> +#include <drm/drm_writeback.h>
>  #include <linux/sync_file.h>
>  
>  #include "drm_crtc_internal.h"
> @@ -646,6 +647,12 @@ static int drm_atomic_connector_check(struct drm_connector *connector,
>  		return -EINVAL;
>  	}
>  
> +	if (state->out_fence && !state->fb) {
> +		DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] requesting out-fence without framebuffer\n",
> +				 connector->base.id, connector->name);
> +		return -EINVAL;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -1047,6 +1054,8 @@ int drm_atomic_connector_set_property(struct drm_connector *connector,
>  		drm_atomic_set_fb_for_connector(state, fb);
>  		if (fb)
>  			drm_framebuffer_unreference(fb);
> +	} else if (property == config->prop_out_fence_ptr) {
> +		state->out_fence_ptr = u64_to_user_ptr(val);

We need to move this out of the conn_state. For my v6 on CRTC out fences
I added drm_atomic_set_out_fence_for_crtc() and
drm_atomic_get_out_fence_for_crtc(). See padovan/fences.

>  	} else if (connector->funcs->atomic_set_property) {
>  		return connector->funcs->atomic_set_property(connector,
>  				state, property, val);
> @@ -1088,6 +1097,8 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
>  	} else if (property == config->writeback_fb_id_property) {
>  		/* Writeback framebuffer is one-shot, write and forget */
>  		*val = 0;
> +	} else if (property == config->prop_out_fence_ptr) {
> +		*val = 0;
>  	} else if (connector->funcs->atomic_get_property) {
>  		return connector->funcs->atomic_get_property(connector,
>  				state, property, val);
> @@ -1736,6 +1747,39 @@ static int setup_out_fence(struct drm_out_fence_state *fence_state,
>  	return 0;
>  }
>  
> +static int setup_connector_out_fences(struct drm_atomic_state *state,
> +				      struct drm_out_fence_state *fence_state,
> +				      int *fence_idx)
> +{
> +	struct drm_connector *conn;
> +	struct drm_connector_state *conn_state;
> +	int i, ret;
> +
> +	for_each_connector_in_state(state, conn, conn_state, i) {
> +		struct fence *fence;
> +
> +		if (!conn_state->out_fence_ptr)
> +			continue;
> +
> +		fence = drm_writeback_get_out_fence(conn, conn_state);
> +		if (!fence)
> +			return -ENOMEM;
> +
> +		ret = setup_out_fence(&fence_state[(*fence_idx)++],
> +				      conn_state->out_fence_ptr,
> +				      fence);
> +		if (ret) {
> +			fence_put(fence);
> +			return ret;
> +		}
> +
> +		/* One-time usage only */
> +		conn_state->out_fence_ptr = NULL;
> +	}
> +
> +	return 0;
> +}
> +
>  int drm_mode_atomic_ioctl(struct drm_device *dev,
>  			  void *data, struct drm_file *file_priv)
>  {
> @@ -1868,8 +1912,8 @@ retry:
>  		drm_mode_object_unreference(obj);
>  	}
>  
> -	fence_state = kcalloc(dev->mode_config.num_crtc, sizeof(*fence_state),
> -			      GFP_KERNEL);
> +	fence_state = kcalloc(dev->mode_config.num_crtc + state->num_connector,
> +			      sizeof(*fence_state), GFP_KERNEL);
>  	if (!fence_state) {
>  		ret = -ENOMEM;
>  		goto out;
> @@ -1929,10 +1973,16 @@ retry:
>  		 * Below we call drm_atomic_state_free for it.
>  		 */
>  		ret = drm_atomic_check_only(state);
> -	} else if (arg->flags & DRM_MODE_ATOMIC_NONBLOCK) {
> -		ret = drm_atomic_nonblocking_commit(state);
>  	} else {
> -		ret = drm_atomic_commit(state);
> +		ret = setup_connector_out_fences(state, fence_state,
> +						 &fence_idx);
> +		if (ret)
> +			goto out;

I'd do this before this block. At the DRM_MODE_ATOMIC_TEST_ONLY or we
check or we commit. Moreover you should check if out_fences
are not set with TEST_ONLY.

> +
> +		if (arg->flags & DRM_MODE_ATOMIC_NONBLOCK)
> +			ret = drm_atomic_nonblocking_commit(state);
> +		else
> +			ret = drm_atomic_commit(state);
>  	}
>  
>  	if (!ret)
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index bba8672..88da299 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -3234,8 +3234,9 @@ __drm_atomic_helper_connector_duplicate_state(struct drm_connector *connector,
>  	if (state->crtc)
>  		drm_connector_reference(connector);
>  
> -	/* Don't copy over framebuffers, they are used only once */
> +	/* Don't copy over framebuffers or fences, they are used only once */
>  	state->fb = NULL;
> +	state->out_fence = NULL;
>  }
>  EXPORT_SYMBOL(__drm_atomic_helper_connector_duplicate_state);
>  
> @@ -3365,6 +3366,8 @@ __drm_atomic_helper_connector_destroy_state(struct drm_connector_state *state)
>  		drm_connector_unreference(state->connector);
>  	if (state->fb)
>  		drm_framebuffer_unreference(state->fb);
> +
> +	fence_put(state->out_fence);
>  }
>  EXPORT_SYMBOL(__drm_atomic_helper_connector_destroy_state);
>  
> diff --git a/drivers/gpu/drm/drm_writeback.c b/drivers/gpu/drm/drm_writeback.c
> index 5a6e0ad..4a6ef30 100644
> --- a/drivers/gpu/drm/drm_writeback.c
> +++ b/drivers/gpu/drm/drm_writeback.c
> @@ -11,6 +11,7 @@
>  #include <drm/drm_crtc.h>
>  #include <drm/drm_property.h>
>  #include <drm/drmP.h>
> +#include <linux/fence.h>
>  
>  /**
>   * DOC: overview
> @@ -32,6 +33,16 @@
>   * explicitly cleared in order to make a subsequent commit which doesn't use
>   * writeback.
>   *
> + * Unlike with planes, when a writeback framebuffer is removed by userspace DRM
> + * makes no attempt to remove it from active use by the connector. This is
> + * because no method is provided to abort a writeback operation, and in any
> + * case making a new commit whilst a writeback is ongoing is undefined (see
> + * OUT_FENCE_PTR below). As soon as the current writeback is finished, the
> + * framebuffer will automatically no longer be in active use. As it will also
> + * have already been removed from the framebuffer list, there will be no way for
> + * any userspace application to retrieve a reference to it in the intervening
> + * period.
> + *
>   * Writeback connectors have several additional properties, which userspace
>   * can use to query and control them:
>   *
> @@ -52,8 +63,48 @@
>   *  "PIXEL_FORMATS_SIZE":
>   *	Immutable unsigned range property storing the number of entries in the
>   *	PIXEL_FORMATS array.
> + *
> + *  "OUT_FENCE_PTR":
> + *	Userspace can provide the address of a 64-bit integer in this property,
> + *	which will be filled with a sync_file file descriptor by the kernel.
> + *	The sync_file will signal when the associated writeback has finished.
> + *	Userspace should wait for this fence to signal before making another
> + *	commit affecting any of the same CRTCs, Planes or Connectors.
> + *	**Failure to do so will result in undefined behaviour.**
> + *	For this reason it is strongly recommended that all userspace
> + *	applications making use of writeback connectors *always* retrieve an
> + *	out-fence for the commit and use it appropriately.
> + *	From userspace, this property will always read as zero.
>   */
>  
> +#define fence_to_connector(x) container_of(x->lock, struct drm_connector, fence_lock)
> +
> +static const char *drm_writeback_fence_get_driver_name(struct fence *fence)
> +{
> +	struct drm_connector *connector = fence_to_connector(fence);
> +
> +	return connector->dev->driver->name;
> +}
> +
> +static const char *drm_writeback_fence_get_timeline_name(struct fence *fence)
> +{
> +	struct drm_connector *connector = fence_to_connector(fence);
> +
> +	return connector->timeline_name;
> +}
> +
> +static bool drm_writeback_fence_enable_signaling(struct fence *fence)
> +{
> +	return true;
> +}
> +
> +static const struct fence_ops drm_writeback_fence_ops = {
> +	.get_driver_name = drm_writeback_fence_get_driver_name,
> +	.get_timeline_name = drm_writeback_fence_get_timeline_name,
> +	.enable_signaling = drm_writeback_fence_enable_signaling,
> +	.wait = fence_default_wait,
> +};
> +
>  /**
>   * create_writeback_properties - Create writeback connector-specific properties
>   * @dev: DRM device
> @@ -136,6 +187,14 @@ int drm_writeback_connector_init(struct drm_device *dev,
>  	if (ret)
>  		goto fail;
>  
> +	connector->fence_context = fence_context_alloc(1);
> +	spin_lock_init(&connector->fence_lock);
> +	snprintf(connector->timeline_name, sizeof(connector->timeline_name),
> +		 "CONNECTOR:%d", connector->base.id);
> +
> +	drm_object_attach_property(&connector->base,
> +				   config->prop_out_fence_ptr, 0);
> +
>  	drm_object_attach_property(&connector->base,
>  				   config->writeback_fb_id_property, 0);
>  
> @@ -155,3 +214,24 @@ fail:
>  	return ret;
>  }
>  EXPORT_SYMBOL(drm_writeback_connector_init);
> +
> +struct fence *drm_writeback_get_out_fence(struct drm_connector *connector,
> +					  struct drm_connector_state *conn_state)
> +{
> +	struct fence *fence;
> +
> +	if (WARN_ON(connector->connector_type != DRM_MODE_CONNECTOR_WRITEBACK))
> +		return NULL;
> +
> +	fence = kzalloc(sizeof(*fence), GFP_KERNEL);
> +	if (!fence)
> +		return NULL;
> +
> +	fence_init(fence, &drm_writeback_fence_ops, &connector->fence_lock,
> +		   connector->fence_context, ++connector->fence_seqno);
> +
> +	conn_state->out_fence = fence_get(fence);
> +
> +	return fence;
> +}
> +EXPORT_SYMBOL(drm_writeback_get_out_fence);
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index a5e3778..7d40537 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -199,6 +199,7 @@ int drm_display_info_set_bus_formats(struct drm_display_info *info,
>   * @best_encoder: can be used by helpers and drivers to select the encoder
>   * @state: backpointer to global drm_atomic_state
>   * @fb: Writeback framebuffer, for DRM_MODE_CONNECTOR_WRITEBACK
> + * @out_fence: Fence which will clear when the framebuffer write has finished
>   */
>  struct drm_connector_state {
>  	struct drm_connector *connector;
> @@ -216,6 +217,9 @@ struct drm_connector_state {
>  	struct drm_atomic_state *state;
>  
>  	struct drm_framebuffer *fb;  /* do not write directly, use drm_atomic_set_fb_for_connector() */
> +
> +	struct fence *out_fence;
> +	u64 __user *out_fence_ptr;
>  };
>  
>  /**
> @@ -546,6 +550,10 @@ struct drm_cmdline_mode {
>   * @tile_v_loc: vertical location of this tile
>   * @tile_h_size: horizontal size of this tile.
>   * @tile_v_size: vertical size of this tile.
> + * @fence_context: context for fence signalling
> + * @fence_lock: fence lock for the fence context
> + * @fence_seqno: seqno variable to create fences
> + * @timeline_name: fence timeline name
>   *
>   * Each connector may be connected to one or more CRTCs, or may be clonable by
>   * another connector if they can share a CRTC.  Each connector also has a specific
> @@ -694,6 +702,12 @@ struct drm_connector {
>  	uint8_t num_h_tile, num_v_tile;
>  	uint8_t tile_h_loc, tile_v_loc;
>  	uint16_t tile_h_size, tile_v_size;
> +
> +	/* fence timelines info for DRM out-fences */
> +	unsigned int fence_context;
> +	spinlock_t fence_lock;
> +	unsigned long fence_seqno;
> +	char timeline_name[32];
>  };
>  
>  #define obj_to_connector(x) container_of(x, struct drm_connector, base)
> diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h
> index afdc2742..01f33bc 100644
> --- a/include/drm/drm_writeback.h
> +++ b/include/drm/drm_writeback.h
> @@ -16,4 +16,6 @@ int drm_writeback_connector_init(struct drm_device *dev,
>  				 const struct drm_connector_funcs *funcs,
>  				 u32 *formats, int n_formats);
>  
> +struct fence *drm_writeback_get_out_fence(struct drm_connector *connector,
> +					  struct drm_connector_state *conn_state);
>  #endif
> -- 
> 1.7.9.5
> 
> _______________________________________________
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> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
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Brian Starkey Oct. 27, 2016, 10:07 a.m. UTC | #4
Hi Gustavo,

On Wed, Oct 26, 2016 at 07:40:29PM -0200, Gustavo Padovan wrote:
>2016-10-26 Brian Starkey <brian.starkey@arm.com>:
>
>> Add the OUT_FENCE_PTR property to writeback connectors, to enable
>> userspace to get a fence which will signal once the writeback is
>> complete.
>>
>> A timeline is added to drm_connector for use by the writeback
>> out-fences. It is up to drivers to check for a fence in the
>> connector_state and signal the it appropriately when their writeback has
>> finished.
>>
>> It is not allowed to request an out-fence without a framebuffer attached
>> to the connector.
>>
>> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
>> ---
>>  drivers/gpu/drm/drm_atomic.c        |   60 +++++++++++++++++++++++---
>>  drivers/gpu/drm/drm_atomic_helper.c |    5 ++-
>>  drivers/gpu/drm/drm_writeback.c     |   80 +++++++++++++++++++++++++++++++++++
>>  include/drm/drm_connector.h         |   14 ++++++
>>  include/drm/drm_writeback.h         |    2 +
>>  5 files changed, 155 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
>> index 3f8fc97..061ea13 100644
>> --- a/drivers/gpu/drm/drm_atomic.c
>> +++ b/drivers/gpu/drm/drm_atomic.c
>> @@ -30,6 +30,7 @@
>>  #include <drm/drm_atomic.h>
>>  #include <drm/drm_mode.h>
>>  #include <drm/drm_plane_helper.h>
>> +#include <drm/drm_writeback.h>
>>  #include <linux/sync_file.h>
>>
>>  #include "drm_crtc_internal.h"
>> @@ -646,6 +647,12 @@ static int drm_atomic_connector_check(struct drm_connector *connector,
>>  		return -EINVAL;
>>  	}
>>
>> +	if (state->out_fence && !state->fb) {
>> +		DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] requesting out-fence without framebuffer\n",
>> +				 connector->base.id, connector->name);
>> +		return -EINVAL;
>> +	}
>> +
>>  	return 0;
>>  }
>>
>> @@ -1047,6 +1054,8 @@ int drm_atomic_connector_set_property(struct drm_connector *connector,
>>  		drm_atomic_set_fb_for_connector(state, fb);
>>  		if (fb)
>>  			drm_framebuffer_unreference(fb);
>> +	} else if (property == config->prop_out_fence_ptr) {
>> +		state->out_fence_ptr = u64_to_user_ptr(val);
>
>We need to move this out of the conn_state. For my v6 on CRTC out fences
>I added drm_atomic_set_out_fence_for_crtc() and
>drm_atomic_get_out_fence_for_crtc(). See padovan/fences.
>

Yep, will do. I was expecting this to change

>>  	} else if (connector->funcs->atomic_set_property) {
>>  		return connector->funcs->atomic_set_property(connector,
>>  				state, property, val);
>> @@ -1088,6 +1097,8 @@ drm_atomic_connector_get_property(struct drm_connector *connector,
>>  	} else if (property == config->writeback_fb_id_property) {
>>  		/* Writeback framebuffer is one-shot, write and forget */
>>  		*val = 0;
>> +	} else if (property == config->prop_out_fence_ptr) {
>> +		*val = 0;
>>  	} else if (connector->funcs->atomic_get_property) {
>>  		return connector->funcs->atomic_get_property(connector,
>>  				state, property, val);
>> @@ -1736,6 +1747,39 @@ static int setup_out_fence(struct drm_out_fence_state *fence_state,
>>  	return 0;
>>  }
>>
>> +static int setup_connector_out_fences(struct drm_atomic_state *state,
>> +				      struct drm_out_fence_state *fence_state,
>> +				      int *fence_idx)
>> +{
>> +	struct drm_connector *conn;
>> +	struct drm_connector_state *conn_state;
>> +	int i, ret;
>> +
>> +	for_each_connector_in_state(state, conn, conn_state, i) {
>> +		struct fence *fence;
>> +
>> +		if (!conn_state->out_fence_ptr)
>> +			continue;
>> +
>> +		fence = drm_writeback_get_out_fence(conn, conn_state);
>> +		if (!fence)
>> +			return -ENOMEM;
>> +
>> +		ret = setup_out_fence(&fence_state[(*fence_idx)++],
>> +				      conn_state->out_fence_ptr,
>> +				      fence);
>> +		if (ret) {
>> +			fence_put(fence);
>> +			return ret;
>> +		}
>> +
>> +		/* One-time usage only */
>> +		conn_state->out_fence_ptr = NULL;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>>  int drm_mode_atomic_ioctl(struct drm_device *dev,
>>  			  void *data, struct drm_file *file_priv)
>>  {
>> @@ -1868,8 +1912,8 @@ retry:
>>  		drm_mode_object_unreference(obj);
>>  	}
>>
>> -	fence_state = kcalloc(dev->mode_config.num_crtc, sizeof(*fence_state),
>> -			      GFP_KERNEL);
>> +	fence_state = kcalloc(dev->mode_config.num_crtc + state->num_connector,
>> +			      sizeof(*fence_state), GFP_KERNEL);
>>  	if (!fence_state) {
>>  		ret = -ENOMEM;
>>  		goto out;
>> @@ -1929,10 +1973,16 @@ retry:
>>  		 * Below we call drm_atomic_state_free for it.
>>  		 */
>>  		ret = drm_atomic_check_only(state);
>> -	} else if (arg->flags & DRM_MODE_ATOMIC_NONBLOCK) {
>> -		ret = drm_atomic_nonblocking_commit(state);
>>  	} else {
>> -		ret = drm_atomic_commit(state);
>> +		ret = setup_connector_out_fences(state, fence_state,
>> +						 &fence_idx);
>> +		if (ret)
>> +			goto out;
>
>I'd do this before this block. At the DRM_MODE_ATOMIC_TEST_ONLY or we
>check or we commit. Moreover you should check if out_fences
>are not set with TEST_ONLY.
>

I don't quite follow the second sentence; you mean you'd rather I
was finished setting things up before the TEST_ONLY check? That sounds
OK.

For TEST_ONLY I actually think we shouldn't reject commits with
OUT_FENCE_PTRs and TEST_ONLY. I thought the idea of TEST_ONLY was for
userspace to build a commit, then see if it can work, then commit it
for real.

By rejecting TEST_ONLY + OUT_FENCE_PTRs you're saying userspace can
never test what it actually intends to commit. It has to test, then
add the out-fences, then commit and hope for the best.

How about always setting the out-fences to -1 for TEST_ONLY?

Thanks for the review,
-Brian

>> +
>> +		if (arg->flags & DRM_MODE_ATOMIC_NONBLOCK)
>> +			ret = drm_atomic_nonblocking_commit(state);
>> +		else
>> +			ret = drm_atomic_commit(state);
>>  	}
>>
>>  	if (!ret)
>> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
>> index bba8672..88da299 100644
>> --- a/drivers/gpu/drm/drm_atomic_helper.c
>> +++ b/drivers/gpu/drm/drm_atomic_helper.c
>> @@ -3234,8 +3234,9 @@ __drm_atomic_helper_connector_duplicate_state(struct drm_connector *connector,
>>  	if (state->crtc)
>>  		drm_connector_reference(connector);
>>
>> -	/* Don't copy over framebuffers, they are used only once */
>> +	/* Don't copy over framebuffers or fences, they are used only once */
>>  	state->fb = NULL;
>> +	state->out_fence = NULL;
>>  }
>>  EXPORT_SYMBOL(__drm_atomic_helper_connector_duplicate_state);
>>
>> @@ -3365,6 +3366,8 @@ __drm_atomic_helper_connector_destroy_state(struct drm_connector_state *state)
>>  		drm_connector_unreference(state->connector);
>>  	if (state->fb)
>>  		drm_framebuffer_unreference(state->fb);
>> +
>> +	fence_put(state->out_fence);
>>  }
>>  EXPORT_SYMBOL(__drm_atomic_helper_connector_destroy_state);
>>
>> diff --git a/drivers/gpu/drm/drm_writeback.c b/drivers/gpu/drm/drm_writeback.c
>> index 5a6e0ad..4a6ef30 100644
>> --- a/drivers/gpu/drm/drm_writeback.c
>> +++ b/drivers/gpu/drm/drm_writeback.c
>> @@ -11,6 +11,7 @@
>>  #include <drm/drm_crtc.h>
>>  #include <drm/drm_property.h>
>>  #include <drm/drmP.h>
>> +#include <linux/fence.h>
>>
>>  /**
>>   * DOC: overview
>> @@ -32,6 +33,16 @@
>>   * explicitly cleared in order to make a subsequent commit which doesn't use
>>   * writeback.
>>   *
>> + * Unlike with planes, when a writeback framebuffer is removed by userspace DRM
>> + * makes no attempt to remove it from active use by the connector. This is
>> + * because no method is provided to abort a writeback operation, and in any
>> + * case making a new commit whilst a writeback is ongoing is undefined (see
>> + * OUT_FENCE_PTR below). As soon as the current writeback is finished, the
>> + * framebuffer will automatically no longer be in active use. As it will also
>> + * have already been removed from the framebuffer list, there will be no way for
>> + * any userspace application to retrieve a reference to it in the intervening
>> + * period.
>> + *
>>   * Writeback connectors have several additional properties, which userspace
>>   * can use to query and control them:
>>   *
>> @@ -52,8 +63,48 @@
>>   *  "PIXEL_FORMATS_SIZE":
>>   *	Immutable unsigned range property storing the number of entries in the
>>   *	PIXEL_FORMATS array.
>> + *
>> + *  "OUT_FENCE_PTR":
>> + *	Userspace can provide the address of a 64-bit integer in this property,
>> + *	which will be filled with a sync_file file descriptor by the kernel.
>> + *	The sync_file will signal when the associated writeback has finished.
>> + *	Userspace should wait for this fence to signal before making another
>> + *	commit affecting any of the same CRTCs, Planes or Connectors.
>> + *	**Failure to do so will result in undefined behaviour.**
>> + *	For this reason it is strongly recommended that all userspace
>> + *	applications making use of writeback connectors *always* retrieve an
>> + *	out-fence for the commit and use it appropriately.
>> + *	From userspace, this property will always read as zero.
>>   */
>>
>> +#define fence_to_connector(x) container_of(x->lock, struct drm_connector, fence_lock)
>> +
>> +static const char *drm_writeback_fence_get_driver_name(struct fence *fence)
>> +{
>> +	struct drm_connector *connector = fence_to_connector(fence);
>> +
>> +	return connector->dev->driver->name;
>> +}
>> +
>> +static const char *drm_writeback_fence_get_timeline_name(struct fence *fence)
>> +{
>> +	struct drm_connector *connector = fence_to_connector(fence);
>> +
>> +	return connector->timeline_name;
>> +}
>> +
>> +static bool drm_writeback_fence_enable_signaling(struct fence *fence)
>> +{
>> +	return true;
>> +}
>> +
>> +static const struct fence_ops drm_writeback_fence_ops = {
>> +	.get_driver_name = drm_writeback_fence_get_driver_name,
>> +	.get_timeline_name = drm_writeback_fence_get_timeline_name,
>> +	.enable_signaling = drm_writeback_fence_enable_signaling,
>> +	.wait = fence_default_wait,
>> +};
>> +
>>  /**
>>   * create_writeback_properties - Create writeback connector-specific properties
>>   * @dev: DRM device
>> @@ -136,6 +187,14 @@ int drm_writeback_connector_init(struct drm_device *dev,
>>  	if (ret)
>>  		goto fail;
>>
>> +	connector->fence_context = fence_context_alloc(1);
>> +	spin_lock_init(&connector->fence_lock);
>> +	snprintf(connector->timeline_name, sizeof(connector->timeline_name),
>> +		 "CONNECTOR:%d", connector->base.id);
>> +
>> +	drm_object_attach_property(&connector->base,
>> +				   config->prop_out_fence_ptr, 0);
>> +
>>  	drm_object_attach_property(&connector->base,
>>  				   config->writeback_fb_id_property, 0);
>>
>> @@ -155,3 +214,24 @@ fail:
>>  	return ret;
>>  }
>>  EXPORT_SYMBOL(drm_writeback_connector_init);
>> +
>> +struct fence *drm_writeback_get_out_fence(struct drm_connector *connector,
>> +					  struct drm_connector_state *conn_state)
>> +{
>> +	struct fence *fence;
>> +
>> +	if (WARN_ON(connector->connector_type != DRM_MODE_CONNECTOR_WRITEBACK))
>> +		return NULL;
>> +
>> +	fence = kzalloc(sizeof(*fence), GFP_KERNEL);
>> +	if (!fence)
>> +		return NULL;
>> +
>> +	fence_init(fence, &drm_writeback_fence_ops, &connector->fence_lock,
>> +		   connector->fence_context, ++connector->fence_seqno);
>> +
>> +	conn_state->out_fence = fence_get(fence);
>> +
>> +	return fence;
>> +}
>> +EXPORT_SYMBOL(drm_writeback_get_out_fence);
>> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
>> index a5e3778..7d40537 100644
>> --- a/include/drm/drm_connector.h
>> +++ b/include/drm/drm_connector.h
>> @@ -199,6 +199,7 @@ int drm_display_info_set_bus_formats(struct drm_display_info *info,
>>   * @best_encoder: can be used by helpers and drivers to select the encoder
>>   * @state: backpointer to global drm_atomic_state
>>   * @fb: Writeback framebuffer, for DRM_MODE_CONNECTOR_WRITEBACK
>> + * @out_fence: Fence which will clear when the framebuffer write has finished
>>   */
>>  struct drm_connector_state {
>>  	struct drm_connector *connector;
>> @@ -216,6 +217,9 @@ struct drm_connector_state {
>>  	struct drm_atomic_state *state;
>>
>>  	struct drm_framebuffer *fb;  /* do not write directly, use drm_atomic_set_fb_for_connector() */
>> +
>> +	struct fence *out_fence;
>> +	u64 __user *out_fence_ptr;
>>  };
>>
>>  /**
>> @@ -546,6 +550,10 @@ struct drm_cmdline_mode {
>>   * @tile_v_loc: vertical location of this tile
>>   * @tile_h_size: horizontal size of this tile.
>>   * @tile_v_size: vertical size of this tile.
>> + * @fence_context: context for fence signalling
>> + * @fence_lock: fence lock for the fence context
>> + * @fence_seqno: seqno variable to create fences
>> + * @timeline_name: fence timeline name
>>   *
>>   * Each connector may be connected to one or more CRTCs, or may be clonable by
>>   * another connector if they can share a CRTC.  Each connector also has a specific
>> @@ -694,6 +702,12 @@ struct drm_connector {
>>  	uint8_t num_h_tile, num_v_tile;
>>  	uint8_t tile_h_loc, tile_v_loc;
>>  	uint16_t tile_h_size, tile_v_size;
>> +
>> +	/* fence timelines info for DRM out-fences */
>> +	unsigned int fence_context;
>> +	spinlock_t fence_lock;
>> +	unsigned long fence_seqno;
>> +	char timeline_name[32];
>>  };
>>
>>  #define obj_to_connector(x) container_of(x, struct drm_connector, base)
>> diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h
>> index afdc2742..01f33bc 100644
>> --- a/include/drm/drm_writeback.h
>> +++ b/include/drm/drm_writeback.h
>> @@ -16,4 +16,6 @@ int drm_writeback_connector_init(struct drm_device *dev,
>>  				 const struct drm_connector_funcs *funcs,
>>  				 u32 *formats, int n_formats);
>>
>> +struct fence *drm_writeback_get_out_fence(struct drm_connector *connector,
>> +					  struct drm_connector_state *conn_state);
>>  #endif
>> --
>> 1.7.9.5
>>
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
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Patch

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 3f8fc97..061ea13 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -30,6 +30,7 @@ 
 #include <drm/drm_atomic.h>
 #include <drm/drm_mode.h>
 #include <drm/drm_plane_helper.h>
+#include <drm/drm_writeback.h>
 #include <linux/sync_file.h>
 
 #include "drm_crtc_internal.h"
@@ -646,6 +647,12 @@  static int drm_atomic_connector_check(struct drm_connector *connector,
 		return -EINVAL;
 	}
 
+	if (state->out_fence && !state->fb) {
+		DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] requesting out-fence without framebuffer\n",
+				 connector->base.id, connector->name);
+		return -EINVAL;
+	}
+
 	return 0;
 }
 
@@ -1047,6 +1054,8 @@  int drm_atomic_connector_set_property(struct drm_connector *connector,
 		drm_atomic_set_fb_for_connector(state, fb);
 		if (fb)
 			drm_framebuffer_unreference(fb);
+	} else if (property == config->prop_out_fence_ptr) {
+		state->out_fence_ptr = u64_to_user_ptr(val);
 	} else if (connector->funcs->atomic_set_property) {
 		return connector->funcs->atomic_set_property(connector,
 				state, property, val);
@@ -1088,6 +1097,8 @@  drm_atomic_connector_get_property(struct drm_connector *connector,
 	} else if (property == config->writeback_fb_id_property) {
 		/* Writeback framebuffer is one-shot, write and forget */
 		*val = 0;
+	} else if (property == config->prop_out_fence_ptr) {
+		*val = 0;
 	} else if (connector->funcs->atomic_get_property) {
 		return connector->funcs->atomic_get_property(connector,
 				state, property, val);
@@ -1736,6 +1747,39 @@  static int setup_out_fence(struct drm_out_fence_state *fence_state,
 	return 0;
 }
 
+static int setup_connector_out_fences(struct drm_atomic_state *state,
+				      struct drm_out_fence_state *fence_state,
+				      int *fence_idx)
+{
+	struct drm_connector *conn;
+	struct drm_connector_state *conn_state;
+	int i, ret;
+
+	for_each_connector_in_state(state, conn, conn_state, i) {
+		struct fence *fence;
+
+		if (!conn_state->out_fence_ptr)
+			continue;
+
+		fence = drm_writeback_get_out_fence(conn, conn_state);
+		if (!fence)
+			return -ENOMEM;
+
+		ret = setup_out_fence(&fence_state[(*fence_idx)++],
+				      conn_state->out_fence_ptr,
+				      fence);
+		if (ret) {
+			fence_put(fence);
+			return ret;
+		}
+
+		/* One-time usage only */
+		conn_state->out_fence_ptr = NULL;
+	}
+
+	return 0;
+}
+
 int drm_mode_atomic_ioctl(struct drm_device *dev,
 			  void *data, struct drm_file *file_priv)
 {
@@ -1868,8 +1912,8 @@  retry:
 		drm_mode_object_unreference(obj);
 	}
 
-	fence_state = kcalloc(dev->mode_config.num_crtc, sizeof(*fence_state),
-			      GFP_KERNEL);
+	fence_state = kcalloc(dev->mode_config.num_crtc + state->num_connector,
+			      sizeof(*fence_state), GFP_KERNEL);
 	if (!fence_state) {
 		ret = -ENOMEM;
 		goto out;
@@ -1929,10 +1973,16 @@  retry:
 		 * Below we call drm_atomic_state_free for it.
 		 */
 		ret = drm_atomic_check_only(state);
-	} else if (arg->flags & DRM_MODE_ATOMIC_NONBLOCK) {
-		ret = drm_atomic_nonblocking_commit(state);
 	} else {
-		ret = drm_atomic_commit(state);
+		ret = setup_connector_out_fences(state, fence_state,
+						 &fence_idx);
+		if (ret)
+			goto out;
+
+		if (arg->flags & DRM_MODE_ATOMIC_NONBLOCK)
+			ret = drm_atomic_nonblocking_commit(state);
+		else
+			ret = drm_atomic_commit(state);
 	}
 
 	if (!ret)
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index bba8672..88da299 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -3234,8 +3234,9 @@  __drm_atomic_helper_connector_duplicate_state(struct drm_connector *connector,
 	if (state->crtc)
 		drm_connector_reference(connector);
 
-	/* Don't copy over framebuffers, they are used only once */
+	/* Don't copy over framebuffers or fences, they are used only once */
 	state->fb = NULL;
+	state->out_fence = NULL;
 }
 EXPORT_SYMBOL(__drm_atomic_helper_connector_duplicate_state);
 
@@ -3365,6 +3366,8 @@  __drm_atomic_helper_connector_destroy_state(struct drm_connector_state *state)
 		drm_connector_unreference(state->connector);
 	if (state->fb)
 		drm_framebuffer_unreference(state->fb);
+
+	fence_put(state->out_fence);
 }
 EXPORT_SYMBOL(__drm_atomic_helper_connector_destroy_state);
 
diff --git a/drivers/gpu/drm/drm_writeback.c b/drivers/gpu/drm/drm_writeback.c
index 5a6e0ad..4a6ef30 100644
--- a/drivers/gpu/drm/drm_writeback.c
+++ b/drivers/gpu/drm/drm_writeback.c
@@ -11,6 +11,7 @@ 
 #include <drm/drm_crtc.h>
 #include <drm/drm_property.h>
 #include <drm/drmP.h>
+#include <linux/fence.h>
 
 /**
  * DOC: overview
@@ -32,6 +33,16 @@ 
  * explicitly cleared in order to make a subsequent commit which doesn't use
  * writeback.
  *
+ * Unlike with planes, when a writeback framebuffer is removed by userspace DRM
+ * makes no attempt to remove it from active use by the connector. This is
+ * because no method is provided to abort a writeback operation, and in any
+ * case making a new commit whilst a writeback is ongoing is undefined (see
+ * OUT_FENCE_PTR below). As soon as the current writeback is finished, the
+ * framebuffer will automatically no longer be in active use. As it will also
+ * have already been removed from the framebuffer list, there will be no way for
+ * any userspace application to retrieve a reference to it in the intervening
+ * period.
+ *
  * Writeback connectors have several additional properties, which userspace
  * can use to query and control them:
  *
@@ -52,8 +63,48 @@ 
  *  "PIXEL_FORMATS_SIZE":
  *	Immutable unsigned range property storing the number of entries in the
  *	PIXEL_FORMATS array.
+ *
+ *  "OUT_FENCE_PTR":
+ *	Userspace can provide the address of a 64-bit integer in this property,
+ *	which will be filled with a sync_file file descriptor by the kernel.
+ *	The sync_file will signal when the associated writeback has finished.
+ *	Userspace should wait for this fence to signal before making another
+ *	commit affecting any of the same CRTCs, Planes or Connectors.
+ *	**Failure to do so will result in undefined behaviour.**
+ *	For this reason it is strongly recommended that all userspace
+ *	applications making use of writeback connectors *always* retrieve an
+ *	out-fence for the commit and use it appropriately.
+ *	From userspace, this property will always read as zero.
  */
 
+#define fence_to_connector(x) container_of(x->lock, struct drm_connector, fence_lock)
+
+static const char *drm_writeback_fence_get_driver_name(struct fence *fence)
+{
+	struct drm_connector *connector = fence_to_connector(fence);
+
+	return connector->dev->driver->name;
+}
+
+static const char *drm_writeback_fence_get_timeline_name(struct fence *fence)
+{
+	struct drm_connector *connector = fence_to_connector(fence);
+
+	return connector->timeline_name;
+}
+
+static bool drm_writeback_fence_enable_signaling(struct fence *fence)
+{
+	return true;
+}
+
+static const struct fence_ops drm_writeback_fence_ops = {
+	.get_driver_name = drm_writeback_fence_get_driver_name,
+	.get_timeline_name = drm_writeback_fence_get_timeline_name,
+	.enable_signaling = drm_writeback_fence_enable_signaling,
+	.wait = fence_default_wait,
+};
+
 /**
  * create_writeback_properties - Create writeback connector-specific properties
  * @dev: DRM device
@@ -136,6 +187,14 @@  int drm_writeback_connector_init(struct drm_device *dev,
 	if (ret)
 		goto fail;
 
+	connector->fence_context = fence_context_alloc(1);
+	spin_lock_init(&connector->fence_lock);
+	snprintf(connector->timeline_name, sizeof(connector->timeline_name),
+		 "CONNECTOR:%d", connector->base.id);
+
+	drm_object_attach_property(&connector->base,
+				   config->prop_out_fence_ptr, 0);
+
 	drm_object_attach_property(&connector->base,
 				   config->writeback_fb_id_property, 0);
 
@@ -155,3 +214,24 @@  fail:
 	return ret;
 }
 EXPORT_SYMBOL(drm_writeback_connector_init);
+
+struct fence *drm_writeback_get_out_fence(struct drm_connector *connector,
+					  struct drm_connector_state *conn_state)
+{
+	struct fence *fence;
+
+	if (WARN_ON(connector->connector_type != DRM_MODE_CONNECTOR_WRITEBACK))
+		return NULL;
+
+	fence = kzalloc(sizeof(*fence), GFP_KERNEL);
+	if (!fence)
+		return NULL;
+
+	fence_init(fence, &drm_writeback_fence_ops, &connector->fence_lock,
+		   connector->fence_context, ++connector->fence_seqno);
+
+	conn_state->out_fence = fence_get(fence);
+
+	return fence;
+}
+EXPORT_SYMBOL(drm_writeback_get_out_fence);
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index a5e3778..7d40537 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -199,6 +199,7 @@  int drm_display_info_set_bus_formats(struct drm_display_info *info,
  * @best_encoder: can be used by helpers and drivers to select the encoder
  * @state: backpointer to global drm_atomic_state
  * @fb: Writeback framebuffer, for DRM_MODE_CONNECTOR_WRITEBACK
+ * @out_fence: Fence which will clear when the framebuffer write has finished
  */
 struct drm_connector_state {
 	struct drm_connector *connector;
@@ -216,6 +217,9 @@  struct drm_connector_state {
 	struct drm_atomic_state *state;
 
 	struct drm_framebuffer *fb;  /* do not write directly, use drm_atomic_set_fb_for_connector() */
+
+	struct fence *out_fence;
+	u64 __user *out_fence_ptr;
 };
 
 /**
@@ -546,6 +550,10 @@  struct drm_cmdline_mode {
  * @tile_v_loc: vertical location of this tile
  * @tile_h_size: horizontal size of this tile.
  * @tile_v_size: vertical size of this tile.
+ * @fence_context: context for fence signalling
+ * @fence_lock: fence lock for the fence context
+ * @fence_seqno: seqno variable to create fences
+ * @timeline_name: fence timeline name
  *
  * Each connector may be connected to one or more CRTCs, or may be clonable by
  * another connector if they can share a CRTC.  Each connector also has a specific
@@ -694,6 +702,12 @@  struct drm_connector {
 	uint8_t num_h_tile, num_v_tile;
 	uint8_t tile_h_loc, tile_v_loc;
 	uint16_t tile_h_size, tile_v_size;
+
+	/* fence timelines info for DRM out-fences */
+	unsigned int fence_context;
+	spinlock_t fence_lock;
+	unsigned long fence_seqno;
+	char timeline_name[32];
 };
 
 #define obj_to_connector(x) container_of(x, struct drm_connector, base)
diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h
index afdc2742..01f33bc 100644
--- a/include/drm/drm_writeback.h
+++ b/include/drm/drm_writeback.h
@@ -16,4 +16,6 @@  int drm_writeback_connector_init(struct drm_device *dev,
 				 const struct drm_connector_funcs *funcs,
 				 u32 *formats, int n_formats);
 
+struct fence *drm_writeback_get_out_fence(struct drm_connector *connector,
+					  struct drm_connector_state *conn_state);
 #endif