LinuxTV Patchwork dma-buf: add struct dma_buf_attach_info v2

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Submitter =?UTF-8?q?Christian=20K=C3=B6nig?=
Date April 30, 2019, 11:10 a.m.
Message ID <20190430111002.106168-1-christian.koenig@amd.com>
Download mbox | patch
Permalink /patch/55949/
State Rejected
Headers show

Comments

=?UTF-8?q?Christian=20K=C3=B6nig?= - April 30, 2019, 11:10 a.m.
Add a structure for the parameters of dma_buf_attach, this makes it much easier
to add new parameters later on.

v2: rebase cleanup and fix all new implementations as well

Signed-off-by: Christian König <christian.koenig@amd.com>
---
 drivers/dma-buf/dma-buf.c                       | 13 +++++++------
 drivers/gpu/drm/armada/armada_gem.c             |  6 +++++-
 drivers/gpu/drm/drm_prime.c                     |  6 +++++-
 drivers/gpu/drm/i915/i915_gem_dmabuf.c          |  6 +++++-
 drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c       |  6 +++++-
 drivers/gpu/drm/tegra/gem.c                     |  6 +++++-
 drivers/gpu/drm/udl/udl_dmabuf.c                |  6 +++++-
 .../common/videobuf2/videobuf2-dma-contig.c     |  6 +++++-
 .../media/common/videobuf2/videobuf2-dma-sg.c   |  6 +++++-
 drivers/misc/fastrpc.c                          |  6 +++++-
 drivers/staging/media/tegra-vde/tegra-vde.c     |  6 +++++-
 drivers/xen/gntdev-dmabuf.c                     |  4 ++++
 include/linux/dma-buf.h                         | 17 +++++++++++++++--
 13 files changed, 76 insertions(+), 18 deletions(-)
Boris Ostrovsky - April 30, 2019, 4:59 p.m.
On 4/30/19 7:10 AM, Christian König wrote:
> diff --git a/drivers/xen/gntdev-dmabuf.c b/drivers/xen/gntdev-dmabuf.c
> index 2c4f324f8626..cacca830b482 100644
> --- a/drivers/xen/gntdev-dmabuf.c
> +++ b/drivers/xen/gntdev-dmabuf.c
> @@ -608,6 +608,7 @@ dmabuf_imp_to_refs(struct gntdev_dmabuf_priv *priv, struct device *dev,
>  		   int fd, int count, int domid)
>  {
>  	struct gntdev_dmabuf *gntdev_dmabuf, *ret;
> +	struct dma_buf_attach_info attach_info;
>  	struct dma_buf *dma_buf;
>  	struct dma_buf_attachment *attach;
>  	struct sg_table *sgt;
> @@ -627,6 +628,9 @@ dmabuf_imp_to_refs(struct gntdev_dmabuf_priv *priv, struct device *dev,
>  	gntdev_dmabuf->priv = priv;
>  	gntdev_dmabuf->fd = fd;
>  
> +	memset(&attach_info, 0, sizeof(attach_info));
> +	attach_info.dev = dev;
> +	attach_info.dmabuf = dma_buf;
>  	attach = dma_buf_attach(dma_buf, dev);
>  	if (IS_ERR(attach)) {
>  		ret = ERR_CAST(attach);

This won't build.

Did you mean

    attach = dma_buf_attach(&attach_info);

?

-boris
Russell King - ARM Linux - April 30, 2019, 5:31 p.m.
On Tue, Apr 30, 2019 at 01:10:02PM +0200, Christian König wrote:
> Add a structure for the parameters of dma_buf_attach, this makes it much easier
> to add new parameters later on.

I don't understand this reasoning.  What are the "new parameters" that
are being proposed, and why do we need to put them into memory to pass
them across this interface?

If the intention is to make it easier to change the interface, passing
parameters in this manner mean that it's easy for the interface to
change and drivers not to notice the changes, since the compiler will
not warn (unless some member of the structure that the driver is using
gets removed, in which case it will error.)

Additions to the structure will go unnoticed by drivers - what if the
caller is expecting some different kind of behaviour, and the driver
ignores that new addition?

This doesn't seem to me like a good idea.

> 
> v2: rebase cleanup and fix all new implementations as well
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>  drivers/dma-buf/dma-buf.c                       | 13 +++++++------
>  drivers/gpu/drm/armada/armada_gem.c             |  6 +++++-
>  drivers/gpu/drm/drm_prime.c                     |  6 +++++-
>  drivers/gpu/drm/i915/i915_gem_dmabuf.c          |  6 +++++-
>  drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c       |  6 +++++-
>  drivers/gpu/drm/tegra/gem.c                     |  6 +++++-
>  drivers/gpu/drm/udl/udl_dmabuf.c                |  6 +++++-
>  .../common/videobuf2/videobuf2-dma-contig.c     |  6 +++++-
>  .../media/common/videobuf2/videobuf2-dma-sg.c   |  6 +++++-
>  drivers/misc/fastrpc.c                          |  6 +++++-
>  drivers/staging/media/tegra-vde/tegra-vde.c     |  6 +++++-
>  drivers/xen/gntdev-dmabuf.c                     |  4 ++++
>  include/linux/dma-buf.h                         | 17 +++++++++++++++--
>  13 files changed, 76 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 3ae6c0c2cc02..e295e76a8c57 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -535,8 +535,9 @@ EXPORT_SYMBOL_GPL(dma_buf_put);
>  /**
>   * dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
>   * calls attach() of dma_buf_ops to allow device-specific attach functionality
> - * @dmabuf:	[in]	buffer to attach device to.
> - * @dev:	[in]	device to be attached.
> + * @info:	[in]	holds all the attach related information provided
> + *			by the importer. see &struct dma_buf_attach_info
> + *			for further details.
>   *
>   * Returns struct dma_buf_attachment pointer for this attachment. Attachments
>   * must be cleaned up by calling dma_buf_detach().
> @@ -550,20 +551,20 @@ EXPORT_SYMBOL_GPL(dma_buf_put);
>   * accessible to @dev, and cannot be moved to a more suitable place. This is
>   * indicated with the error code -EBUSY.
>   */
> -struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> -					  struct device *dev)
> +struct dma_buf_attachment *dma_buf_attach(const struct dma_buf_attach_info *info)
>  {
> +	struct dma_buf *dmabuf = info->dmabuf;
>  	struct dma_buf_attachment *attach;
>  	int ret;
>  
> -	if (WARN_ON(!dmabuf || !dev))
> +	if (WARN_ON(!dmabuf || !info->dev))
>  		return ERR_PTR(-EINVAL);
>  
>  	attach = kzalloc(sizeof(*attach), GFP_KERNEL);
>  	if (!attach)
>  		return ERR_PTR(-ENOMEM);
>  
> -	attach->dev = dev;
> +	attach->dev = info->dev;
>  	attach->dmabuf = dmabuf;
>  
>  	mutex_lock(&dmabuf->lock);
> diff --git a/drivers/gpu/drm/armada/armada_gem.c b/drivers/gpu/drm/armada/armada_gem.c
> index 642d0e70d0f8..19c47821032f 100644
> --- a/drivers/gpu/drm/armada/armada_gem.c
> +++ b/drivers/gpu/drm/armada/armada_gem.c
> @@ -501,6 +501,10 @@ armada_gem_prime_export(struct drm_device *dev, struct drm_gem_object *obj,
>  struct drm_gem_object *
>  armada_gem_prime_import(struct drm_device *dev, struct dma_buf *buf)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = dev->dev,
> +		.dmabuf = buf
> +	};
>  	struct dma_buf_attachment *attach;
>  	struct armada_gem_object *dobj;
>  
> @@ -516,7 +520,7 @@ armada_gem_prime_import(struct drm_device *dev, struct dma_buf *buf)
>  		}
>  	}
>  
> -	attach = dma_buf_attach(buf, dev->dev);
> +	attach = dma_buf_attach(&attach_info);
>  	if (IS_ERR(attach))
>  		return ERR_CAST(attach);
>  
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index dc079efb3b0f..1dd70fc095ee 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -710,6 +710,10 @@ struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
>  					    struct dma_buf *dma_buf,
>  					    struct device *attach_dev)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = attach_dev,
> +		.dmabuf = dma_buf
> +	};
>  	struct dma_buf_attachment *attach;
>  	struct sg_table *sgt;
>  	struct drm_gem_object *obj;
> @@ -730,7 +734,7 @@ struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
>  	if (!dev->driver->gem_prime_import_sg_table)
>  		return ERR_PTR(-EINVAL);
>  
> -	attach = dma_buf_attach(dma_buf, attach_dev);
> +	attach = dma_buf_attach(&attach_info);
>  	if (IS_ERR(attach))
>  		return ERR_CAST(attach);
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
> index 5a101a9462d8..978054157c64 100644
> --- a/drivers/gpu/drm/i915/i915_gem_dmabuf.c
> +++ b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
> @@ -277,6 +277,10 @@ static const struct drm_i915_gem_object_ops i915_gem_object_dmabuf_ops = {
>  struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
>  					     struct dma_buf *dma_buf)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = dev->dev,
> +		.dmabuf = dma_buf
> +	};
>  	struct dma_buf_attachment *attach;
>  	struct drm_i915_gem_object *obj;
>  	int ret;
> @@ -295,7 +299,7 @@ struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
>  	}
>  
>  	/* need to attach */
> -	attach = dma_buf_attach(dma_buf, dev->dev);
> +	attach = dma_buf_attach(&attach_info);
>  	if (IS_ERR(attach))
>  		return ERR_CAST(attach);
>  
> diff --git a/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c b/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
> index 0f8b597ccd10..38d06574b251 100644
> --- a/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
> +++ b/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
> @@ -156,6 +156,10 @@ struct dma_buf *omap_gem_prime_export(struct drm_device *dev,
>  struct drm_gem_object *omap_gem_prime_import(struct drm_device *dev,
>  					     struct dma_buf *dma_buf)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = dev->dev,
> +		.dmabuf = dma_buf
> +	};
>  	struct dma_buf_attachment *attach;
>  	struct drm_gem_object *obj;
>  	struct sg_table *sgt;
> @@ -173,7 +177,7 @@ struct drm_gem_object *omap_gem_prime_import(struct drm_device *dev,
>  		}
>  	}
>  
> -	attach = dma_buf_attach(dma_buf, dev->dev);
> +	attach = dma_buf_attach(&attach_info);
>  	if (IS_ERR(attach))
>  		return ERR_CAST(attach);
>  
> diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
> index 4f80100ff5f3..8e6b6c879add 100644
> --- a/drivers/gpu/drm/tegra/gem.c
> +++ b/drivers/gpu/drm/tegra/gem.c
> @@ -332,6 +332,10 @@ struct tegra_bo *tegra_bo_create_with_handle(struct drm_file *file,
>  static struct tegra_bo *tegra_bo_import(struct drm_device *drm,
>  					struct dma_buf *buf)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = drm->dev,
> +		.dmabuf = buf
> +	};
>  	struct tegra_drm *tegra = drm->dev_private;
>  	struct dma_buf_attachment *attach;
>  	struct tegra_bo *bo;
> @@ -341,7 +345,7 @@ static struct tegra_bo *tegra_bo_import(struct drm_device *drm,
>  	if (IS_ERR(bo))
>  		return bo;
>  
> -	attach = dma_buf_attach(buf, drm->dev);
> +	attach = dma_buf_attach(&attach_info);
>  	if (IS_ERR(attach)) {
>  		err = PTR_ERR(attach);
>  		goto free;
> diff --git a/drivers/gpu/drm/udl/udl_dmabuf.c b/drivers/gpu/drm/udl/udl_dmabuf.c
> index 556f62662aa9..86b928f9742f 100644
> --- a/drivers/gpu/drm/udl/udl_dmabuf.c
> +++ b/drivers/gpu/drm/udl/udl_dmabuf.c
> @@ -226,6 +226,10 @@ static int udl_prime_create(struct drm_device *dev,
>  struct drm_gem_object *udl_gem_prime_import(struct drm_device *dev,
>  				struct dma_buf *dma_buf)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = dev->dev,
> +		.dmabuf = dma_buf
> +	};
>  	struct dma_buf_attachment *attach;
>  	struct sg_table *sg;
>  	struct udl_gem_object *uobj;
> @@ -233,7 +237,7 @@ struct drm_gem_object *udl_gem_prime_import(struct drm_device *dev,
>  
>  	/* need to attach */
>  	get_device(dev->dev);
> -	attach = dma_buf_attach(dma_buf, dev->dev);
> +	attach = dma_buf_attach(&attach_info);
>  	if (IS_ERR(attach)) {
>  		put_device(dev->dev);
>  		return ERR_CAST(attach);
> diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> index 82389aead6ed..b2d844d45ea6 100644
> --- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> +++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> @@ -653,6 +653,10 @@ static void vb2_dc_detach_dmabuf(void *mem_priv)
>  static void *vb2_dc_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
>  	unsigned long size, enum dma_data_direction dma_dir)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = dev,
> +		.dmabuf = dbuf
> +	};
>  	struct vb2_dc_buf *buf;
>  	struct dma_buf_attachment *dba;
>  
> @@ -668,7 +672,7 @@ static void *vb2_dc_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
>  
>  	buf->dev = dev;
>  	/* create attachment for the dmabuf with the user device */
> -	dba = dma_buf_attach(dbuf, buf->dev);
> +	dba = dma_buf_attach(&attach_info);
>  	if (IS_ERR(dba)) {
>  		pr_err("failed to attach dmabuf\n");
>  		kfree(buf);
> diff --git a/drivers/media/common/videobuf2/videobuf2-dma-sg.c b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> index 270c3162fdcb..ddd5f36a8ec7 100644
> --- a/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> +++ b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> @@ -608,6 +608,10 @@ static void vb2_dma_sg_detach_dmabuf(void *mem_priv)
>  static void *vb2_dma_sg_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
>  	unsigned long size, enum dma_data_direction dma_dir)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = dev,
> +		.dmabuf = dbuf
> +	};
>  	struct vb2_dma_sg_buf *buf;
>  	struct dma_buf_attachment *dba;
>  
> @@ -623,7 +627,7 @@ static void *vb2_dma_sg_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
>  
>  	buf->dev = dev;
>  	/* create attachment for the dmabuf with the user device */
> -	dba = dma_buf_attach(dbuf, buf->dev);
> +	dba = dma_buf_attach(&attach_info);
>  	if (IS_ERR(dba)) {
>  		pr_err("failed to attach dmabuf\n");
>  		kfree(buf);
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index 39f832d27288..93d0aac05715 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -482,6 +482,7 @@ static int fastrpc_map_create(struct fastrpc_user *fl, int fd,
>  			      u64 len, struct fastrpc_map **ppmap)
>  {
>  	struct fastrpc_session_ctx *sess = fl->sctx;
> +	struct dma_buf_attach_info attach_info;
>  	struct fastrpc_map *map = NULL;
>  	int err = 0;
>  
> @@ -501,7 +502,10 @@ static int fastrpc_map_create(struct fastrpc_user *fl, int fd,
>  		goto get_err;
>  	}
>  
> -	map->attach = dma_buf_attach(map->buf, sess->dev);
> +	memset(&attach_info, 0, sizeof(attach_info));
> +	attach_info.dev = sess->dev;
> +	attach_info.dmabuf = map->buf;
> +	map->attach = dma_buf_attach(&attach_info);
>  	if (IS_ERR(map->attach)) {
>  		dev_err(sess->dev, "Failed to attach dmabuf\n");
>  		err = PTR_ERR(map->attach);
> diff --git a/drivers/staging/media/tegra-vde/tegra-vde.c b/drivers/staging/media/tegra-vde/tegra-vde.c
> index aa6c6bba961e..5a10c1facc27 100644
> --- a/drivers/staging/media/tegra-vde/tegra-vde.c
> +++ b/drivers/staging/media/tegra-vde/tegra-vde.c
> @@ -568,6 +568,10 @@ static int tegra_vde_attach_dmabuf(struct device *dev,
>  				   size_t *size,
>  				   enum dma_data_direction dma_dir)
>  {
> +	struct dma_buf_attach_info attach_info = {
> +		.dev = dev,
> +		.dmabuf = dmabuf
> +	};
>  	struct dma_buf_attachment *attachment;
>  	struct dma_buf *dmabuf;
>  	struct sg_table *sgt;
> @@ -591,7 +595,7 @@ static int tegra_vde_attach_dmabuf(struct device *dev,
>  		return -EINVAL;
>  	}
>  
> -	attachment = dma_buf_attach(dmabuf, dev);
> +	attachment = dma_buf_attach(&attach_info);
>  	if (IS_ERR(attachment)) {
>  		dev_err(dev, "Failed to attach dmabuf\n");
>  		err = PTR_ERR(attachment);
> diff --git a/drivers/xen/gntdev-dmabuf.c b/drivers/xen/gntdev-dmabuf.c
> index 2c4f324f8626..cacca830b482 100644
> --- a/drivers/xen/gntdev-dmabuf.c
> +++ b/drivers/xen/gntdev-dmabuf.c
> @@ -608,6 +608,7 @@ dmabuf_imp_to_refs(struct gntdev_dmabuf_priv *priv, struct device *dev,
>  		   int fd, int count, int domid)
>  {
>  	struct gntdev_dmabuf *gntdev_dmabuf, *ret;
> +	struct dma_buf_attach_info attach_info;
>  	struct dma_buf *dma_buf;
>  	struct dma_buf_attachment *attach;
>  	struct sg_table *sgt;
> @@ -627,6 +628,9 @@ dmabuf_imp_to_refs(struct gntdev_dmabuf_priv *priv, struct device *dev,
>  	gntdev_dmabuf->priv = priv;
>  	gntdev_dmabuf->fd = fd;
>  
> +	memset(&attach_info, 0, sizeof(attach_info));
> +	attach_info.dev = dev;
> +	attach_info.dmabuf = dma_buf;
>  	attach = dma_buf_attach(dma_buf, dev);
>  	if (IS_ERR(attach)) {
>  		ret = ERR_CAST(attach);
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index a0bd071466fc..b5b0f5e3f186 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -375,6 +375,19 @@ struct dma_buf_export_info {
>  	struct dma_buf_export_info name = { .exp_name = KBUILD_MODNAME, \
>  					 .owner = THIS_MODULE }
>  
> +/**
> + * struct dma_buf_attach_info - holds information needed to attach to a dma_buf
> + * @dmabuf:	the exported dma_buf
> + * @dev:	the device which wants to import the attachment
> + *
> + * This structure holds the information required to attach to a buffer. Used
> + * with dma_buf_attach() only.
> + */
> +struct dma_buf_attach_info {
> +	struct dma_buf *dmabuf;
> +	struct device *dev;
> +};
> +
>  /**
>   * get_dma_buf - convenience wrapper for get_file.
>   * @dmabuf:	[in]	pointer to dma_buf
> @@ -389,8 +402,8 @@ static inline void get_dma_buf(struct dma_buf *dmabuf)
>  	get_file(dmabuf->file);
>  }
>  
> -struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> -							struct device *dev);
> +struct dma_buf_attachment *
> +dma_buf_attach(const struct dma_buf_attach_info *info);
>  void dma_buf_detach(struct dma_buf *dmabuf,
>  				struct dma_buf_attachment *dmabuf_attach);
>  
> -- 
> 2.17.1
> 
>
=?UTF-8?q?Christian=20K=C3=B6nig?= - May 3, 2019, 12:05 p.m.
Am 30.04.19 um 19:31 schrieb Russell King - ARM Linux admin:
> On Tue, Apr 30, 2019 at 01:10:02PM +0200, Christian König wrote:
>> Add a structure for the parameters of dma_buf_attach, this makes it much easier
>> to add new parameters later on.
> I don't understand this reasoning.  What are the "new parameters" that
> are being proposed, and why do we need to put them into memory to pass
> them across this interface?
>
> If the intention is to make it easier to change the interface, passing
> parameters in this manner mean that it's easy for the interface to
> change and drivers not to notice the changes, since the compiler will
> not warn (unless some member of the structure that the driver is using
> gets removed, in which case it will error.)
>
> Additions to the structure will go unnoticed by drivers - what if the
> caller is expecting some different kind of behaviour, and the driver
> ignores that new addition?

Well, exactly that's the intention here: That the drivers using this 
interface should be able to ignore the new additions for now as long as 
they are not going to use them.

The background is that we have multiple interface changes in the 
pipeline, and each step requires new optional parameters.

> This doesn't seem to me like a good idea.

Well, the obvious alternatives are:

a) Change all drivers to explicitly provide NULL/0 for the new parameters.

b) Use a wrapper, so that the function signature of dma_buf_attach stays 
the same.

Key point here is that I have an invalidation callback change, a P2P 
patch set and some locking changes which all require adding new 
parameters or flags. And at each step I would then start to change all 
drivers, adding some more NULL pointers or flags with 0 default value.

I'm actually perfectly fine going down any route, but this just seemed 
to me simplest and with the least risk of breaking anything. Opinions?

Thanks,
Christian.
Daniel Vetter - May 3, 2019, 12:09 p.m.
On Fri, May 03, 2019 at 02:05:47PM +0200, Christian König wrote:
> Am 30.04.19 um 19:31 schrieb Russell King - ARM Linux admin:
> > On Tue, Apr 30, 2019 at 01:10:02PM +0200, Christian König wrote:
> > > Add a structure for the parameters of dma_buf_attach, this makes it much easier
> > > to add new parameters later on.
> > I don't understand this reasoning.  What are the "new parameters" that
> > are being proposed, and why do we need to put them into memory to pass
> > them across this interface?
> > 
> > If the intention is to make it easier to change the interface, passing
> > parameters in this manner mean that it's easy for the interface to
> > change and drivers not to notice the changes, since the compiler will
> > not warn (unless some member of the structure that the driver is using
> > gets removed, in which case it will error.)
> > 
> > Additions to the structure will go unnoticed by drivers - what if the
> > caller is expecting some different kind of behaviour, and the driver
> > ignores that new addition?
> 
> Well, exactly that's the intention here: That the drivers using this
> interface should be able to ignore the new additions for now as long as they
> are not going to use them.
> 
> The background is that we have multiple interface changes in the pipeline,
> and each step requires new optional parameters.
> 
> > This doesn't seem to me like a good idea.
> 
> Well, the obvious alternatives are:
> 
> a) Change all drivers to explicitly provide NULL/0 for the new parameters.
> 
> b) Use a wrapper, so that the function signature of dma_buf_attach stays the
> same.
> 
> Key point here is that I have an invalidation callback change, a P2P patch
> set and some locking changes which all require adding new parameters or
> flags. And at each step I would then start to change all drivers, adding
> some more NULL pointers or flags with 0 default value.
> 
> I'm actually perfectly fine going down any route, but this just seemed to me
> simplest and with the least risk of breaking anything. Opinions?

I think given all our discussions and plans the argument object makes tons
of sense. Much easier to document well than a long list of parameters.
Maybe we should make it const, so it could work like an ops/func table and
we could store it as a pointer in the dma_buf_attachment?
-Daniel
Christian König - May 3, 2019, 12:15 p.m.
Am 03.05.19 um 14:09 schrieb Daniel Vetter:
> [CAUTION: External Email]

>

> On Fri, May 03, 2019 at 02:05:47PM +0200, Christian König wrote:

>> Am 30.04.19 um 19:31 schrieb Russell King - ARM Linux admin:

>>> On Tue, Apr 30, 2019 at 01:10:02PM +0200, Christian König wrote:

>>>> Add a structure for the parameters of dma_buf_attach, this makes it much easier

>>>> to add new parameters later on.

>>> I don't understand this reasoning.  What are the "new parameters" that

>>> are being proposed, and why do we need to put them into memory to pass

>>> them across this interface?

>>>

>>> If the intention is to make it easier to change the interface, passing

>>> parameters in this manner mean that it's easy for the interface to

>>> change and drivers not to notice the changes, since the compiler will

>>> not warn (unless some member of the structure that the driver is using

>>> gets removed, in which case it will error.)

>>>

>>> Additions to the structure will go unnoticed by drivers - what if the

>>> caller is expecting some different kind of behaviour, and the driver

>>> ignores that new addition?

>> Well, exactly that's the intention here: That the drivers using this

>> interface should be able to ignore the new additions for now as long as they

>> are not going to use them.

>>

>> The background is that we have multiple interface changes in the pipeline,

>> and each step requires new optional parameters.

>>

>>> This doesn't seem to me like a good idea.

>> Well, the obvious alternatives are:

>>

>> a) Change all drivers to explicitly provide NULL/0 for the new parameters.

>>

>> b) Use a wrapper, so that the function signature of dma_buf_attach stays the

>> same.

>>

>> Key point here is that I have an invalidation callback change, a P2P patch

>> set and some locking changes which all require adding new parameters or

>> flags. And at each step I would then start to change all drivers, adding

>> some more NULL pointers or flags with 0 default value.

>>

>> I'm actually perfectly fine going down any route, but this just seemed to me

>> simplest and with the least risk of breaking anything. Opinions?

> I think given all our discussions and plans the argument object makes tons

> of sense. Much easier to document well than a long list of parameters.

> Maybe we should make it const, so it could work like an ops/func table and

> we could store it as a pointer in the dma_buf_attachment?


Yeah, the invalidation callback and P2P flags are constant. But the 
importer_priv field isn't.

We could do something like adding the importer_priv field as parameter 
and the other two as const structure.

Third alternative would be to throw out all the DRM abstraction and just 
embed the attachment structure in the buffer object and get completely 
rid of the importer_priv field (probably the cleanest alternative, but 
also the most work todo).

Christian.

> -Daniel

> --

> Daniel Vetter

> Software Engineer, Intel Corporation

> http://blog.ffwll.ch

Patch

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 3ae6c0c2cc02..e295e76a8c57 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -535,8 +535,9 @@  EXPORT_SYMBOL_GPL(dma_buf_put);
 /**
  * dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
  * calls attach() of dma_buf_ops to allow device-specific attach functionality
- * @dmabuf:	[in]	buffer to attach device to.
- * @dev:	[in]	device to be attached.
+ * @info:	[in]	holds all the attach related information provided
+ *			by the importer. see &struct dma_buf_attach_info
+ *			for further details.
  *
  * Returns struct dma_buf_attachment pointer for this attachment. Attachments
  * must be cleaned up by calling dma_buf_detach().
@@ -550,20 +551,20 @@  EXPORT_SYMBOL_GPL(dma_buf_put);
  * accessible to @dev, and cannot be moved to a more suitable place. This is
  * indicated with the error code -EBUSY.
  */
-struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
-					  struct device *dev)
+struct dma_buf_attachment *dma_buf_attach(const struct dma_buf_attach_info *info)
 {
+	struct dma_buf *dmabuf = info->dmabuf;
 	struct dma_buf_attachment *attach;
 	int ret;
 
-	if (WARN_ON(!dmabuf || !dev))
+	if (WARN_ON(!dmabuf || !info->dev))
 		return ERR_PTR(-EINVAL);
 
 	attach = kzalloc(sizeof(*attach), GFP_KERNEL);
 	if (!attach)
 		return ERR_PTR(-ENOMEM);
 
-	attach->dev = dev;
+	attach->dev = info->dev;
 	attach->dmabuf = dmabuf;
 
 	mutex_lock(&dmabuf->lock);
diff --git a/drivers/gpu/drm/armada/armada_gem.c b/drivers/gpu/drm/armada/armada_gem.c
index 642d0e70d0f8..19c47821032f 100644
--- a/drivers/gpu/drm/armada/armada_gem.c
+++ b/drivers/gpu/drm/armada/armada_gem.c
@@ -501,6 +501,10 @@  armada_gem_prime_export(struct drm_device *dev, struct drm_gem_object *obj,
 struct drm_gem_object *
 armada_gem_prime_import(struct drm_device *dev, struct dma_buf *buf)
 {
+	struct dma_buf_attach_info attach_info = {
+		.dev = dev->dev,
+		.dmabuf = buf
+	};
 	struct dma_buf_attachment *attach;
 	struct armada_gem_object *dobj;
 
@@ -516,7 +520,7 @@  armada_gem_prime_import(struct drm_device *dev, struct dma_buf *buf)
 		}
 	}
 
-	attach = dma_buf_attach(buf, dev->dev);
+	attach = dma_buf_attach(&attach_info);
 	if (IS_ERR(attach))
 		return ERR_CAST(attach);
 
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index dc079efb3b0f..1dd70fc095ee 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -710,6 +710,10 @@  struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
 					    struct dma_buf *dma_buf,
 					    struct device *attach_dev)
 {
+	struct dma_buf_attach_info attach_info = {
+		.dev = attach_dev,
+		.dmabuf = dma_buf
+	};
 	struct dma_buf_attachment *attach;
 	struct sg_table *sgt;
 	struct drm_gem_object *obj;
@@ -730,7 +734,7 @@  struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
 	if (!dev->driver->gem_prime_import_sg_table)
 		return ERR_PTR(-EINVAL);
 
-	attach = dma_buf_attach(dma_buf, attach_dev);
+	attach = dma_buf_attach(&attach_info);
 	if (IS_ERR(attach))
 		return ERR_CAST(attach);
 
diff --git a/drivers/gpu/drm/i915/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
index 5a101a9462d8..978054157c64 100644
--- a/drivers/gpu/drm/i915/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
@@ -277,6 +277,10 @@  static const struct drm_i915_gem_object_ops i915_gem_object_dmabuf_ops = {
 struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
 					     struct dma_buf *dma_buf)
 {
+	struct dma_buf_attach_info attach_info = {
+		.dev = dev->dev,
+		.dmabuf = dma_buf
+	};
 	struct dma_buf_attachment *attach;
 	struct drm_i915_gem_object *obj;
 	int ret;
@@ -295,7 +299,7 @@  struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
 	}
 
 	/* need to attach */
-	attach = dma_buf_attach(dma_buf, dev->dev);
+	attach = dma_buf_attach(&attach_info);
 	if (IS_ERR(attach))
 		return ERR_CAST(attach);
 
diff --git a/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c b/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
index 0f8b597ccd10..38d06574b251 100644
--- a/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
+++ b/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
@@ -156,6 +156,10 @@  struct dma_buf *omap_gem_prime_export(struct drm_device *dev,
 struct drm_gem_object *omap_gem_prime_import(struct drm_device *dev,
 					     struct dma_buf *dma_buf)
 {
+	struct dma_buf_attach_info attach_info = {
+		.dev = dev->dev,
+		.dmabuf = dma_buf
+	};
 	struct dma_buf_attachment *attach;
 	struct drm_gem_object *obj;
 	struct sg_table *sgt;
@@ -173,7 +177,7 @@  struct drm_gem_object *omap_gem_prime_import(struct drm_device *dev,
 		}
 	}
 
-	attach = dma_buf_attach(dma_buf, dev->dev);
+	attach = dma_buf_attach(&attach_info);
 	if (IS_ERR(attach))
 		return ERR_CAST(attach);
 
diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
index 4f80100ff5f3..8e6b6c879add 100644
--- a/drivers/gpu/drm/tegra/gem.c
+++ b/drivers/gpu/drm/tegra/gem.c
@@ -332,6 +332,10 @@  struct tegra_bo *tegra_bo_create_with_handle(struct drm_file *file,
 static struct tegra_bo *tegra_bo_import(struct drm_device *drm,
 					struct dma_buf *buf)
 {
+	struct dma_buf_attach_info attach_info = {
+		.dev = drm->dev,
+		.dmabuf = buf
+	};
 	struct tegra_drm *tegra = drm->dev_private;
 	struct dma_buf_attachment *attach;
 	struct tegra_bo *bo;
@@ -341,7 +345,7 @@  static struct tegra_bo *tegra_bo_import(struct drm_device *drm,
 	if (IS_ERR(bo))
 		return bo;
 
-	attach = dma_buf_attach(buf, drm->dev);
+	attach = dma_buf_attach(&attach_info);
 	if (IS_ERR(attach)) {
 		err = PTR_ERR(attach);
 		goto free;
diff --git a/drivers/gpu/drm/udl/udl_dmabuf.c b/drivers/gpu/drm/udl/udl_dmabuf.c
index 556f62662aa9..86b928f9742f 100644
--- a/drivers/gpu/drm/udl/udl_dmabuf.c
+++ b/drivers/gpu/drm/udl/udl_dmabuf.c
@@ -226,6 +226,10 @@  static int udl_prime_create(struct drm_device *dev,
 struct drm_gem_object *udl_gem_prime_import(struct drm_device *dev,
 				struct dma_buf *dma_buf)
 {
+	struct dma_buf_attach_info attach_info = {
+		.dev = dev->dev,
+		.dmabuf = dma_buf
+	};
 	struct dma_buf_attachment *attach;
 	struct sg_table *sg;
 	struct udl_gem_object *uobj;
@@ -233,7 +237,7 @@  struct drm_gem_object *udl_gem_prime_import(struct drm_device *dev,
 
 	/* need to attach */
 	get_device(dev->dev);
-	attach = dma_buf_attach(dma_buf, dev->dev);
+	attach = dma_buf_attach(&attach_info);
 	if (IS_ERR(attach)) {
 		put_device(dev->dev);
 		return ERR_CAST(attach);
diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
index 82389aead6ed..b2d844d45ea6 100644
--- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c
+++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
@@ -653,6 +653,10 @@  static void vb2_dc_detach_dmabuf(void *mem_priv)
 static void *vb2_dc_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
 	unsigned long size, enum dma_data_direction dma_dir)
 {
+	struct dma_buf_attach_info attach_info = {
+		.dev = dev,
+		.dmabuf = dbuf
+	};
 	struct vb2_dc_buf *buf;
 	struct dma_buf_attachment *dba;
 
@@ -668,7 +672,7 @@  static void *vb2_dc_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
 
 	buf->dev = dev;
 	/* create attachment for the dmabuf with the user device */
-	dba = dma_buf_attach(dbuf, buf->dev);
+	dba = dma_buf_attach(&attach_info);
 	if (IS_ERR(dba)) {
 		pr_err("failed to attach dmabuf\n");
 		kfree(buf);
diff --git a/drivers/media/common/videobuf2/videobuf2-dma-sg.c b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
index 270c3162fdcb..ddd5f36a8ec7 100644
--- a/drivers/media/common/videobuf2/videobuf2-dma-sg.c
+++ b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
@@ -608,6 +608,10 @@  static void vb2_dma_sg_detach_dmabuf(void *mem_priv)
 static void *vb2_dma_sg_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
 	unsigned long size, enum dma_data_direction dma_dir)
 {
+	struct dma_buf_attach_info attach_info = {
+		.dev = dev,
+		.dmabuf = dbuf
+	};
 	struct vb2_dma_sg_buf *buf;
 	struct dma_buf_attachment *dba;
 
@@ -623,7 +627,7 @@  static void *vb2_dma_sg_attach_dmabuf(struct device *dev, struct dma_buf *dbuf,
 
 	buf->dev = dev;
 	/* create attachment for the dmabuf with the user device */
-	dba = dma_buf_attach(dbuf, buf->dev);
+	dba = dma_buf_attach(&attach_info);
 	if (IS_ERR(dba)) {
 		pr_err("failed to attach dmabuf\n");
 		kfree(buf);
diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 39f832d27288..93d0aac05715 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -482,6 +482,7 @@  static int fastrpc_map_create(struct fastrpc_user *fl, int fd,
 			      u64 len, struct fastrpc_map **ppmap)
 {
 	struct fastrpc_session_ctx *sess = fl->sctx;
+	struct dma_buf_attach_info attach_info;
 	struct fastrpc_map *map = NULL;
 	int err = 0;
 
@@ -501,7 +502,10 @@  static int fastrpc_map_create(struct fastrpc_user *fl, int fd,
 		goto get_err;
 	}
 
-	map->attach = dma_buf_attach(map->buf, sess->dev);
+	memset(&attach_info, 0, sizeof(attach_info));
+	attach_info.dev = sess->dev;
+	attach_info.dmabuf = map->buf;
+	map->attach = dma_buf_attach(&attach_info);
 	if (IS_ERR(map->attach)) {
 		dev_err(sess->dev, "Failed to attach dmabuf\n");
 		err = PTR_ERR(map->attach);
diff --git a/drivers/staging/media/tegra-vde/tegra-vde.c b/drivers/staging/media/tegra-vde/tegra-vde.c
index aa6c6bba961e..5a10c1facc27 100644
--- a/drivers/staging/media/tegra-vde/tegra-vde.c
+++ b/drivers/staging/media/tegra-vde/tegra-vde.c
@@ -568,6 +568,10 @@  static int tegra_vde_attach_dmabuf(struct device *dev,
 				   size_t *size,
 				   enum dma_data_direction dma_dir)
 {
+	struct dma_buf_attach_info attach_info = {
+		.dev = dev,
+		.dmabuf = dmabuf
+	};
 	struct dma_buf_attachment *attachment;
 	struct dma_buf *dmabuf;
 	struct sg_table *sgt;
@@ -591,7 +595,7 @@  static int tegra_vde_attach_dmabuf(struct device *dev,
 		return -EINVAL;
 	}
 
-	attachment = dma_buf_attach(dmabuf, dev);
+	attachment = dma_buf_attach(&attach_info);
 	if (IS_ERR(attachment)) {
 		dev_err(dev, "Failed to attach dmabuf\n");
 		err = PTR_ERR(attachment);
diff --git a/drivers/xen/gntdev-dmabuf.c b/drivers/xen/gntdev-dmabuf.c
index 2c4f324f8626..cacca830b482 100644
--- a/drivers/xen/gntdev-dmabuf.c
+++ b/drivers/xen/gntdev-dmabuf.c
@@ -608,6 +608,7 @@  dmabuf_imp_to_refs(struct gntdev_dmabuf_priv *priv, struct device *dev,
 		   int fd, int count, int domid)
 {
 	struct gntdev_dmabuf *gntdev_dmabuf, *ret;
+	struct dma_buf_attach_info attach_info;
 	struct dma_buf *dma_buf;
 	struct dma_buf_attachment *attach;
 	struct sg_table *sgt;
@@ -627,6 +628,9 @@  dmabuf_imp_to_refs(struct gntdev_dmabuf_priv *priv, struct device *dev,
 	gntdev_dmabuf->priv = priv;
 	gntdev_dmabuf->fd = fd;
 
+	memset(&attach_info, 0, sizeof(attach_info));
+	attach_info.dev = dev;
+	attach_info.dmabuf = dma_buf;
 	attach = dma_buf_attach(dma_buf, dev);
 	if (IS_ERR(attach)) {
 		ret = ERR_CAST(attach);
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index a0bd071466fc..b5b0f5e3f186 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -375,6 +375,19 @@  struct dma_buf_export_info {
 	struct dma_buf_export_info name = { .exp_name = KBUILD_MODNAME, \
 					 .owner = THIS_MODULE }
 
+/**
+ * struct dma_buf_attach_info - holds information needed to attach to a dma_buf
+ * @dmabuf:	the exported dma_buf
+ * @dev:	the device which wants to import the attachment
+ *
+ * This structure holds the information required to attach to a buffer. Used
+ * with dma_buf_attach() only.
+ */
+struct dma_buf_attach_info {
+	struct dma_buf *dmabuf;
+	struct device *dev;
+};
+
 /**
  * get_dma_buf - convenience wrapper for get_file.
  * @dmabuf:	[in]	pointer to dma_buf
@@ -389,8 +402,8 @@  static inline void get_dma_buf(struct dma_buf *dmabuf)
 	get_file(dmabuf->file);
 }
 
-struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
-							struct device *dev);
+struct dma_buf_attachment *
+dma_buf_attach(const struct dma_buf_attach_info *info);
 void dma_buf_detach(struct dma_buf *dmabuf,
 				struct dma_buf_attachment *dmabuf_attach);
 

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