LinuxTV Patchwork [v6,08/18] media: vsp1: wpf: Add writeback support

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Submitter Laurent Pinchart
Date March 13, 2019, 12:05 a.m.
Message ID <20190313000532.7087-9-laurent.pinchart+renesas@ideasonboard.com>
Download mbox | patch
Permalink /patch/55022/
State New
Headers show

Comments

Laurent Pinchart - March 13, 2019, 12:05 a.m.
Add support for the writeback feature of the WPF, to enable capturing
frames at the WPF output for display pipelines. To enable writeback the
vsp1_rwpf structure mem field must be set to the address of the
writeback buffer and the writeback field set to true before the WPF
.configure_stream() and .configure_partition() are called. The WPF will
enable writeback in the display list for a single frame, and writeback
will then be automatically disabled.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
---
 drivers/media/platform/vsp1/vsp1_rwpf.h |  2 +
 drivers/media/platform/vsp1/vsp1_wpf.c  | 73 ++++++++++++++++++++++---
 2 files changed, 66 insertions(+), 9 deletions(-)
Kieran Bingham - March 13, 2019, 10:59 a.m.
Hi Laurent,

On 13/03/2019 00:05, Laurent Pinchart wrote:
> Add support for the writeback feature of the WPF, to enable capturing
> frames at the WPF output for display pipelines. To enable writeback the
> vsp1_rwpf structure mem field must be set to the address of the
> writeback buffer and the writeback field set to true before the WPF
> .configure_stream() and .configure_partition() are called. The WPF will
> enable writeback in the display list for a single frame, and writeback
> will then be automatically disabled.
> 

This looks good.

Took some time to go through it while I argue with myself, but I think I
reached an agreement with me in the end :)

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>


> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> ---
>  drivers/media/platform/vsp1/vsp1_rwpf.h |  2 +
>  drivers/media/platform/vsp1/vsp1_wpf.c  | 73 ++++++++++++++++++++++---
>  2 files changed, 66 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/media/platform/vsp1/vsp1_rwpf.h b/drivers/media/platform/vsp1/vsp1_rwpf.h
> index 70742ecf766f..910990b27617 100644
> --- a/drivers/media/platform/vsp1/vsp1_rwpf.h
> +++ b/drivers/media/platform/vsp1/vsp1_rwpf.h
> @@ -35,6 +35,7 @@ struct vsp1_rwpf {
>  	struct v4l2_ctrl_handler ctrls;
>  
>  	struct vsp1_video *video;
> +	bool has_writeback;
>  
>  	unsigned int max_width;
>  	unsigned int max_height;
> @@ -61,6 +62,7 @@ struct vsp1_rwpf {
>  	} flip;
>  
>  	struct vsp1_rwpf_memory mem;
> +	bool writeback;


Does this need to be initialised to false somewhere?

answering my own question;
 No - because we allocate the "struct vsp1_rwpf *wpf" with devm_kzalloc.

>  
>  	struct vsp1_dl_manager *dlm;
>  };
> diff --git a/drivers/media/platform/vsp1/vsp1_wpf.c b/drivers/media/platform/vsp1/vsp1_wpf.c
> index fc5c1b0f6633..390ac478336d 100644
> --- a/drivers/media/platform/vsp1/vsp1_wpf.c
> +++ b/drivers/media/platform/vsp1/vsp1_wpf.c
> @@ -232,6 +232,27 @@ static void vsp1_wpf_destroy(struct vsp1_entity *entity)
>  	vsp1_dlm_destroy(wpf->dlm);
>  }
>  
> +static int wpf_configure_writeback_chain(struct vsp1_rwpf *wpf,
> +					 struct vsp1_dl_list *dl)
> +{
> +	unsigned int index = wpf->entity.index;
> +	struct vsp1_dl_list *dl_next;
> +	struct vsp1_dl_body *dlb;
> +
> +	dl_next = vsp1_dl_list_get(wpf->dlm);> +	if (!dl_next) {
> +		dev_err(wpf->entity.vsp1->dev,
> +			"Failed to obtain a dl list, disabling writeback\n");
> +		return -ENOMEM;
> +	}
> +
> +	dlb = vsp1_dl_list_get_body0(dl_next);
> +	vsp1_dl_body_write(dlb, VI6_WPF_WRBCK_CTRL(index), 0);
> +	vsp1_dl_list_add_chain(dl, dl_next);

Two thoughts for future consideration.

1) There was a patch I had floated to reduce the allocations of the pool
sizes. This would need to be checked if it's ever reconsidered, as we
now use an extra DL.

This is currently allocated as 64 lists in vsp1_wpf_create() with:

 	wpf->dlm = vsp1_dlm_create(vsp1, index, 64);

which is actually 65 lists because there's a + 1 in vsp1_dlm_create(),
so I think we have more than we'll ever need for a display pipeline
currently.


2) I did think we could pre-allocate this write back display list and
re-use it, by always attaching the same "writeback disable display list"
to the chain.

If we do that - we'll have to be careful about the refcounting of the
chained list as it will automatically be put back on to the dlm->free
list currently when the frame completes.

I think it's probably only a small optimisation to re-use the list
anyway, so just getting a new one and chaining it is certainly adequate
for this solution.



> +
> +	return 0;
> +}
> +
>  static void wpf_configure_stream(struct vsp1_entity *entity,
>  				 struct vsp1_pipeline *pipe,
>  				 struct vsp1_dl_list *dl,
> @@ -241,9 +262,11 @@ static void wpf_configure_stream(struct vsp1_entity *entity,
>  	struct vsp1_device *vsp1 = wpf->entity.vsp1;
>  	const struct v4l2_mbus_framefmt *source_format;
>  	const struct v4l2_mbus_framefmt *sink_format;
> +	unsigned int index = wpf->entity.index;
>  	unsigned int i;
>  	u32 outfmt = 0;
>  	u32 srcrpf = 0;
> +	int ret;
>  
>  	sink_format = vsp1_entity_get_pad_format(&wpf->entity,
>  						 wpf->entity.config,
> @@ -251,8 +274,9 @@ static void wpf_configure_stream(struct vsp1_entity *entity,
>  	source_format = vsp1_entity_get_pad_format(&wpf->entity,
>  						   wpf->entity.config,
>  						   RWPF_PAD_SOURCE);
> +
>  	/* Format */
> -	if (!pipe->lif) {
> +	if (!pipe->lif || wpf->writeback) {
>  		const struct v4l2_pix_format_mplane *format = &wpf->format;
>  		const struct vsp1_format_info *fmtinfo = wpf->fmtinfo;
>  
> @@ -277,8 +301,7 @@ static void wpf_configure_stream(struct vsp1_entity *entity,
>  
>  		vsp1_wpf_write(wpf, dlb, VI6_WPF_DSWAP, fmtinfo->swap);
>  
> -		if (vsp1_feature(vsp1, VSP1_HAS_WPF_HFLIP) &&
> -		    wpf->entity.index == 0)
> +		if (vsp1_feature(vsp1, VSP1_HAS_WPF_HFLIP) && index == 0)
>  			vsp1_wpf_write(wpf, dlb, VI6_WPF_ROT_CTRL,
>  				       VI6_WPF_ROT_CTRL_LN16 |
>  				       (256 << VI6_WPF_ROT_CTRL_LMEM_WD_SHIFT));
> @@ -289,11 +312,9 @@ static void wpf_configure_stream(struct vsp1_entity *entity,
>  
>  	wpf->outfmt = outfmt;
>  
> -	vsp1_dl_body_write(dlb, VI6_DPR_WPF_FPORCH(wpf->entity.index),
> +	vsp1_dl_body_write(dlb, VI6_DPR_WPF_FPORCH(index),
>  			   VI6_DPR_WPF_FPORCH_FP_WPFN);
>  
> -	vsp1_dl_body_write(dlb, VI6_WPF_WRBCK_CTRL(wpf->entity.index), 0);
> -
>  	/*
>  	 * Sources. If the pipeline has a single input and BRx is not used,
>  	 * configure it as the master layer. Otherwise configure all
> @@ -319,9 +340,26 @@ static void wpf_configure_stream(struct vsp1_entity *entity,
>  	vsp1_wpf_write(wpf, dlb, VI6_WPF_SRCRPF, srcrpf);
>  
>  	/* Enable interrupts. */
> -	vsp1_dl_body_write(dlb, VI6_WPF_IRQ_STA(wpf->entity.index), 0);
> -	vsp1_dl_body_write(dlb, VI6_WPF_IRQ_ENB(wpf->entity.index),
> +	vsp1_dl_body_write(dlb, VI6_WPF_IRQ_STA(index), 0);
> +	vsp1_dl_body_write(dlb, VI6_WPF_IRQ_ENB(index),
>  			   VI6_WFP_IRQ_ENB_DFEE);
> +
> +	/*
> +	 * Configure writeback for display pipelines (the wpf writeback flag is
> +	 * never set for memory-to-memory pipelines). Start by adding a chained
> +	 * display list to disable writeback after a single frame, and process
> +	 * to enable writeback. If the display list allocation fails don't
> +	 * enable writeback as we wouldn't be able to safely disable it,
> +	 * resulting in possible memory corruption.
> +	 */
> +	if (wpf->writeback) {
> +		ret = wpf_configure_writeback_chain(wpf, dl);
> +		if (ret < 0)
> +			wpf->writeback = false;
> +	}
> +
> +	vsp1_dl_body_write(dlb, VI6_WPF_WRBCK_CTRL(index),
> +			   wpf->writeback ? VI6_WPF_WRBCK_CTRL_WBMD : 0);
>  }
>  
>  static void wpf_configure_frame(struct vsp1_entity *entity,
> @@ -391,7 +429,11 @@ static void wpf_configure_partition(struct vsp1_entity *entity,
>  		       (0 << VI6_WPF_SZCLIP_OFST_SHIFT) |
>  		       (height << VI6_WPF_SZCLIP_SIZE_SHIFT));
>  
> -	if (pipe->lif)
> +	/*
> +	 * For display pipelines without writeback enabled there's no memory
> +	 * address to configure, return now.
> +	 */
> +	if (pipe->lif && !wpf->writeback)
>  		return;
>  
>  	/*
> @@ -480,6 +522,12 @@ static void wpf_configure_partition(struct vsp1_entity *entity,
>  	vsp1_wpf_write(wpf, dlb, VI6_WPF_DSTM_ADDR_Y, mem.addr[0]);
>  	vsp1_wpf_write(wpf, dlb, VI6_WPF_DSTM_ADDR_C0, mem.addr[1]);
>  	vsp1_wpf_write(wpf, dlb, VI6_WPF_DSTM_ADDR_C1, mem.addr[2]);
> +
> +	/*
> +	 * Writeback operates in single-shot mode and lasts for a single frame,
> +	 * reset the writeback flag to false for the next frame.
> +	 */
> +	wpf->writeback = false;
>  }
>  
>  static unsigned int wpf_max_width(struct vsp1_entity *entity,
> @@ -530,6 +578,13 @@ struct vsp1_rwpf *vsp1_wpf_create(struct vsp1_device *vsp1, unsigned int index)
>  		wpf->max_height = WPF_GEN3_MAX_HEIGHT;
>  	}
>  
> +	/*
> +	 * On Gen3 WPFs with a LIF output can also write to memory for display
> +	 * writeback.
> +	 */
> +	if (vsp1->info->gen > 2 && index < vsp1->info->lif_count)
> +		wpf->has_writeback = true;
> +
>  	wpf->entity.ops = &wpf_entity_ops;
>  	wpf->entity.type = VSP1_ENTITY_WPF;
>  	wpf->entity.index = index;
>
Laurent Pinchart - March 13, 2019, 11:15 a.m.
Hi Kieran,

On Wed, Mar 13, 2019 at 10:59:18AM +0000, Kieran Bingham wrote:
> On 13/03/2019 00:05, Laurent Pinchart wrote:
> > Add support for the writeback feature of the WPF, to enable capturing
> > frames at the WPF output for display pipelines. To enable writeback the
> > vsp1_rwpf structure mem field must be set to the address of the
> > writeback buffer and the writeback field set to true before the WPF
> > .configure_stream() and .configure_partition() are called. The WPF will
> > enable writeback in the display list for a single frame, and writeback
> > will then be automatically disabled.
> 
> This looks good.
> 
> Took some time to go through it while I argue with myself, but I think I
> reached an agreement with me in the end :)
> 
> Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
> 
> > Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> > ---
> >  drivers/media/platform/vsp1/vsp1_rwpf.h |  2 +
> >  drivers/media/platform/vsp1/vsp1_wpf.c  | 73 ++++++++++++++++++++++---
> >  2 files changed, 66 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/media/platform/vsp1/vsp1_rwpf.h b/drivers/media/platform/vsp1/vsp1_rwpf.h
> > index 70742ecf766f..910990b27617 100644
> > --- a/drivers/media/platform/vsp1/vsp1_rwpf.h
> > +++ b/drivers/media/platform/vsp1/vsp1_rwpf.h
> > @@ -35,6 +35,7 @@ struct vsp1_rwpf {
> >  	struct v4l2_ctrl_handler ctrls;
> >  
> >  	struct vsp1_video *video;
> > +	bool has_writeback;
> >  
> >  	unsigned int max_width;
> >  	unsigned int max_height;
> > @@ -61,6 +62,7 @@ struct vsp1_rwpf {
> >  	} flip;
> >  
> >  	struct vsp1_rwpf_memory mem;
> > +	bool writeback;
> 
> Does this need to be initialised to false somewhere?
> 
> answering my own question;
>  No - because we allocate the "struct vsp1_rwpf *wpf" with devm_kzalloc.
> 
> >  	struct vsp1_dl_manager *dlm;
> >  };
> > diff --git a/drivers/media/platform/vsp1/vsp1_wpf.c b/drivers/media/platform/vsp1/vsp1_wpf.c
> > index fc5c1b0f6633..390ac478336d 100644
> > --- a/drivers/media/platform/vsp1/vsp1_wpf.c
> > +++ b/drivers/media/platform/vsp1/vsp1_wpf.c
> > @@ -232,6 +232,27 @@ static void vsp1_wpf_destroy(struct vsp1_entity *entity)
> >  	vsp1_dlm_destroy(wpf->dlm);
> >  }
> >  
> > +static int wpf_configure_writeback_chain(struct vsp1_rwpf *wpf,
> > +					 struct vsp1_dl_list *dl)
> > +{
> > +	unsigned int index = wpf->entity.index;
> > +	struct vsp1_dl_list *dl_next;
> > +	struct vsp1_dl_body *dlb;
> > +
> > +	dl_next = vsp1_dl_list_get(wpf->dlm);> +	if (!dl_next) {
> > +		dev_err(wpf->entity.vsp1->dev,
> > +			"Failed to obtain a dl list, disabling writeback\n");
> > +		return -ENOMEM;
> > +	}
> > +
> > +	dlb = vsp1_dl_list_get_body0(dl_next);
> > +	vsp1_dl_body_write(dlb, VI6_WPF_WRBCK_CTRL(index), 0);
> > +	vsp1_dl_list_add_chain(dl, dl_next);
> 
> Two thoughts for future consideration.
> 
> 1) There was a patch I had floated to reduce the allocations of the pool
> sizes. This would need to be checked if it's ever reconsidered, as we
> now use an extra DL.
> 
> This is currently allocated as 64 lists in vsp1_wpf_create() with:
> 
>  	wpf->dlm = vsp1_dlm_create(vsp1, index, 64);
> 
> which is actually 65 lists because there's a + 1 in vsp1_dlm_create(),
> so I think we have more than we'll ever need for a display pipeline
> currently.
> 
> 
> 2) I did think we could pre-allocate this write back display list and
> re-use it, by always attaching the same "writeback disable display list"
> to the chain.
> 
> If we do that - we'll have to be careful about the refcounting of the
> chained list as it will automatically be put back on to the dlm->free
> list currently when the frame completes.

Yes, and that's why I haven't done so yet. I think it can be implemented
on top of this series as it's an optimization.

> I think it's probably only a small optimisation to re-use the list
> anyway, so just getting a new one and chaining it is certainly adequate
> for this solution.
> 
> > +
> > +	return 0;
> > +}
> > +
> >  static void wpf_configure_stream(struct vsp1_entity *entity,
> >  				 struct vsp1_pipeline *pipe,
> >  				 struct vsp1_dl_list *dl,
> > @@ -241,9 +262,11 @@ static void wpf_configure_stream(struct vsp1_entity *entity,
> >  	struct vsp1_device *vsp1 = wpf->entity.vsp1;
> >  	const struct v4l2_mbus_framefmt *source_format;
> >  	const struct v4l2_mbus_framefmt *sink_format;
> > +	unsigned int index = wpf->entity.index;
> >  	unsigned int i;
> >  	u32 outfmt = 0;
> >  	u32 srcrpf = 0;
> > +	int ret;
> >  
> >  	sink_format = vsp1_entity_get_pad_format(&wpf->entity,
> >  						 wpf->entity.config,
> > @@ -251,8 +274,9 @@ static void wpf_configure_stream(struct vsp1_entity *entity,
> >  	source_format = vsp1_entity_get_pad_format(&wpf->entity,
> >  						   wpf->entity.config,
> >  						   RWPF_PAD_SOURCE);
> > +
> >  	/* Format */
> > -	if (!pipe->lif) {
> > +	if (!pipe->lif || wpf->writeback) {
> >  		const struct v4l2_pix_format_mplane *format = &wpf->format;
> >  		const struct vsp1_format_info *fmtinfo = wpf->fmtinfo;
> >  
> > @@ -277,8 +301,7 @@ static void wpf_configure_stream(struct vsp1_entity *entity,
> >  
> >  		vsp1_wpf_write(wpf, dlb, VI6_WPF_DSWAP, fmtinfo->swap);
> >  
> > -		if (vsp1_feature(vsp1, VSP1_HAS_WPF_HFLIP) &&
> > -		    wpf->entity.index == 0)
> > +		if (vsp1_feature(vsp1, VSP1_HAS_WPF_HFLIP) && index == 0)
> >  			vsp1_wpf_write(wpf, dlb, VI6_WPF_ROT_CTRL,
> >  				       VI6_WPF_ROT_CTRL_LN16 |
> >  				       (256 << VI6_WPF_ROT_CTRL_LMEM_WD_SHIFT));
> > @@ -289,11 +312,9 @@ static void wpf_configure_stream(struct vsp1_entity *entity,
> >  
> >  	wpf->outfmt = outfmt;
> >  
> > -	vsp1_dl_body_write(dlb, VI6_DPR_WPF_FPORCH(wpf->entity.index),
> > +	vsp1_dl_body_write(dlb, VI6_DPR_WPF_FPORCH(index),
> >  			   VI6_DPR_WPF_FPORCH_FP_WPFN);
> >  
> > -	vsp1_dl_body_write(dlb, VI6_WPF_WRBCK_CTRL(wpf->entity.index), 0);
> > -
> >  	/*
> >  	 * Sources. If the pipeline has a single input and BRx is not used,
> >  	 * configure it as the master layer. Otherwise configure all
> > @@ -319,9 +340,26 @@ static void wpf_configure_stream(struct vsp1_entity *entity,
> >  	vsp1_wpf_write(wpf, dlb, VI6_WPF_SRCRPF, srcrpf);
> >  
> >  	/* Enable interrupts. */
> > -	vsp1_dl_body_write(dlb, VI6_WPF_IRQ_STA(wpf->entity.index), 0);
> > -	vsp1_dl_body_write(dlb, VI6_WPF_IRQ_ENB(wpf->entity.index),
> > +	vsp1_dl_body_write(dlb, VI6_WPF_IRQ_STA(index), 0);
> > +	vsp1_dl_body_write(dlb, VI6_WPF_IRQ_ENB(index),
> >  			   VI6_WFP_IRQ_ENB_DFEE);
> > +
> > +	/*
> > +	 * Configure writeback for display pipelines (the wpf writeback flag is
> > +	 * never set for memory-to-memory pipelines). Start by adding a chained
> > +	 * display list to disable writeback after a single frame, and process
> > +	 * to enable writeback. If the display list allocation fails don't
> > +	 * enable writeback as we wouldn't be able to safely disable it,
> > +	 * resulting in possible memory corruption.
> > +	 */
> > +	if (wpf->writeback) {
> > +		ret = wpf_configure_writeback_chain(wpf, dl);
> > +		if (ret < 0)
> > +			wpf->writeback = false;
> > +	}
> > +
> > +	vsp1_dl_body_write(dlb, VI6_WPF_WRBCK_CTRL(index),
> > +			   wpf->writeback ? VI6_WPF_WRBCK_CTRL_WBMD : 0);
> >  }
> >  
> >  static void wpf_configure_frame(struct vsp1_entity *entity,
> > @@ -391,7 +429,11 @@ static void wpf_configure_partition(struct vsp1_entity *entity,
> >  		       (0 << VI6_WPF_SZCLIP_OFST_SHIFT) |
> >  		       (height << VI6_WPF_SZCLIP_SIZE_SHIFT));
> >  
> > -	if (pipe->lif)
> > +	/*
> > +	 * For display pipelines without writeback enabled there's no memory
> > +	 * address to configure, return now.
> > +	 */
> > +	if (pipe->lif && !wpf->writeback)
> >  		return;
> >  
> >  	/*
> > @@ -480,6 +522,12 @@ static void wpf_configure_partition(struct vsp1_entity *entity,
> >  	vsp1_wpf_write(wpf, dlb, VI6_WPF_DSTM_ADDR_Y, mem.addr[0]);
> >  	vsp1_wpf_write(wpf, dlb, VI6_WPF_DSTM_ADDR_C0, mem.addr[1]);
> >  	vsp1_wpf_write(wpf, dlb, VI6_WPF_DSTM_ADDR_C1, mem.addr[2]);
> > +
> > +	/*
> > +	 * Writeback operates in single-shot mode and lasts for a single frame,
> > +	 * reset the writeback flag to false for the next frame.
> > +	 */
> > +	wpf->writeback = false;
> >  }
> >  
> >  static unsigned int wpf_max_width(struct vsp1_entity *entity,
> > @@ -530,6 +578,13 @@ struct vsp1_rwpf *vsp1_wpf_create(struct vsp1_device *vsp1, unsigned int index)
> >  		wpf->max_height = WPF_GEN3_MAX_HEIGHT;
> >  	}
> >  
> > +	/*
> > +	 * On Gen3 WPFs with a LIF output can also write to memory for display
> > +	 * writeback.
> > +	 */
> > +	if (vsp1->info->gen > 2 && index < vsp1->info->lif_count)
> > +		wpf->has_writeback = true;
> > +
> >  	wpf->entity.ops = &wpf_entity_ops;
> >  	wpf->entity.type = VSP1_ENTITY_WPF;
> >  	wpf->entity.index = index;

Patch

diff --git a/drivers/media/platform/vsp1/vsp1_rwpf.h b/drivers/media/platform/vsp1/vsp1_rwpf.h
index 70742ecf766f..910990b27617 100644
--- a/drivers/media/platform/vsp1/vsp1_rwpf.h
+++ b/drivers/media/platform/vsp1/vsp1_rwpf.h
@@ -35,6 +35,7 @@  struct vsp1_rwpf {
 	struct v4l2_ctrl_handler ctrls;
 
 	struct vsp1_video *video;
+	bool has_writeback;
 
 	unsigned int max_width;
 	unsigned int max_height;
@@ -61,6 +62,7 @@  struct vsp1_rwpf {
 	} flip;
 
 	struct vsp1_rwpf_memory mem;
+	bool writeback;
 
 	struct vsp1_dl_manager *dlm;
 };
diff --git a/drivers/media/platform/vsp1/vsp1_wpf.c b/drivers/media/platform/vsp1/vsp1_wpf.c
index fc5c1b0f6633..390ac478336d 100644
--- a/drivers/media/platform/vsp1/vsp1_wpf.c
+++ b/drivers/media/platform/vsp1/vsp1_wpf.c
@@ -232,6 +232,27 @@  static void vsp1_wpf_destroy(struct vsp1_entity *entity)
 	vsp1_dlm_destroy(wpf->dlm);
 }
 
+static int wpf_configure_writeback_chain(struct vsp1_rwpf *wpf,
+					 struct vsp1_dl_list *dl)
+{
+	unsigned int index = wpf->entity.index;
+	struct vsp1_dl_list *dl_next;
+	struct vsp1_dl_body *dlb;
+
+	dl_next = vsp1_dl_list_get(wpf->dlm);
+	if (!dl_next) {
+		dev_err(wpf->entity.vsp1->dev,
+			"Failed to obtain a dl list, disabling writeback\n");
+		return -ENOMEM;
+	}
+
+	dlb = vsp1_dl_list_get_body0(dl_next);
+	vsp1_dl_body_write(dlb, VI6_WPF_WRBCK_CTRL(index), 0);
+	vsp1_dl_list_add_chain(dl, dl_next);
+
+	return 0;
+}
+
 static void wpf_configure_stream(struct vsp1_entity *entity,
 				 struct vsp1_pipeline *pipe,
 				 struct vsp1_dl_list *dl,
@@ -241,9 +262,11 @@  static void wpf_configure_stream(struct vsp1_entity *entity,
 	struct vsp1_device *vsp1 = wpf->entity.vsp1;
 	const struct v4l2_mbus_framefmt *source_format;
 	const struct v4l2_mbus_framefmt *sink_format;
+	unsigned int index = wpf->entity.index;
 	unsigned int i;
 	u32 outfmt = 0;
 	u32 srcrpf = 0;
+	int ret;
 
 	sink_format = vsp1_entity_get_pad_format(&wpf->entity,
 						 wpf->entity.config,
@@ -251,8 +274,9 @@  static void wpf_configure_stream(struct vsp1_entity *entity,
 	source_format = vsp1_entity_get_pad_format(&wpf->entity,
 						   wpf->entity.config,
 						   RWPF_PAD_SOURCE);
+
 	/* Format */
-	if (!pipe->lif) {
+	if (!pipe->lif || wpf->writeback) {
 		const struct v4l2_pix_format_mplane *format = &wpf->format;
 		const struct vsp1_format_info *fmtinfo = wpf->fmtinfo;
 
@@ -277,8 +301,7 @@  static void wpf_configure_stream(struct vsp1_entity *entity,
 
 		vsp1_wpf_write(wpf, dlb, VI6_WPF_DSWAP, fmtinfo->swap);
 
-		if (vsp1_feature(vsp1, VSP1_HAS_WPF_HFLIP) &&
-		    wpf->entity.index == 0)
+		if (vsp1_feature(vsp1, VSP1_HAS_WPF_HFLIP) && index == 0)
 			vsp1_wpf_write(wpf, dlb, VI6_WPF_ROT_CTRL,
 				       VI6_WPF_ROT_CTRL_LN16 |
 				       (256 << VI6_WPF_ROT_CTRL_LMEM_WD_SHIFT));
@@ -289,11 +312,9 @@  static void wpf_configure_stream(struct vsp1_entity *entity,
 
 	wpf->outfmt = outfmt;
 
-	vsp1_dl_body_write(dlb, VI6_DPR_WPF_FPORCH(wpf->entity.index),
+	vsp1_dl_body_write(dlb, VI6_DPR_WPF_FPORCH(index),
 			   VI6_DPR_WPF_FPORCH_FP_WPFN);
 
-	vsp1_dl_body_write(dlb, VI6_WPF_WRBCK_CTRL(wpf->entity.index), 0);
-
 	/*
 	 * Sources. If the pipeline has a single input and BRx is not used,
 	 * configure it as the master layer. Otherwise configure all
@@ -319,9 +340,26 @@  static void wpf_configure_stream(struct vsp1_entity *entity,
 	vsp1_wpf_write(wpf, dlb, VI6_WPF_SRCRPF, srcrpf);
 
 	/* Enable interrupts. */
-	vsp1_dl_body_write(dlb, VI6_WPF_IRQ_STA(wpf->entity.index), 0);
-	vsp1_dl_body_write(dlb, VI6_WPF_IRQ_ENB(wpf->entity.index),
+	vsp1_dl_body_write(dlb, VI6_WPF_IRQ_STA(index), 0);
+	vsp1_dl_body_write(dlb, VI6_WPF_IRQ_ENB(index),
 			   VI6_WFP_IRQ_ENB_DFEE);
+
+	/*
+	 * Configure writeback for display pipelines (the wpf writeback flag is
+	 * never set for memory-to-memory pipelines). Start by adding a chained
+	 * display list to disable writeback after a single frame, and process
+	 * to enable writeback. If the display list allocation fails don't
+	 * enable writeback as we wouldn't be able to safely disable it,
+	 * resulting in possible memory corruption.
+	 */
+	if (wpf->writeback) {
+		ret = wpf_configure_writeback_chain(wpf, dl);
+		if (ret < 0)
+			wpf->writeback = false;
+	}
+
+	vsp1_dl_body_write(dlb, VI6_WPF_WRBCK_CTRL(index),
+			   wpf->writeback ? VI6_WPF_WRBCK_CTRL_WBMD : 0);
 }
 
 static void wpf_configure_frame(struct vsp1_entity *entity,
@@ -391,7 +429,11 @@  static void wpf_configure_partition(struct vsp1_entity *entity,
 		       (0 << VI6_WPF_SZCLIP_OFST_SHIFT) |
 		       (height << VI6_WPF_SZCLIP_SIZE_SHIFT));
 
-	if (pipe->lif)
+	/*
+	 * For display pipelines without writeback enabled there's no memory
+	 * address to configure, return now.
+	 */
+	if (pipe->lif && !wpf->writeback)
 		return;
 
 	/*
@@ -480,6 +522,12 @@  static void wpf_configure_partition(struct vsp1_entity *entity,
 	vsp1_wpf_write(wpf, dlb, VI6_WPF_DSTM_ADDR_Y, mem.addr[0]);
 	vsp1_wpf_write(wpf, dlb, VI6_WPF_DSTM_ADDR_C0, mem.addr[1]);
 	vsp1_wpf_write(wpf, dlb, VI6_WPF_DSTM_ADDR_C1, mem.addr[2]);
+
+	/*
+	 * Writeback operates in single-shot mode and lasts for a single frame,
+	 * reset the writeback flag to false for the next frame.
+	 */
+	wpf->writeback = false;
 }
 
 static unsigned int wpf_max_width(struct vsp1_entity *entity,
@@ -530,6 +578,13 @@  struct vsp1_rwpf *vsp1_wpf_create(struct vsp1_device *vsp1, unsigned int index)
 		wpf->max_height = WPF_GEN3_MAX_HEIGHT;
 	}
 
+	/*
+	 * On Gen3 WPFs with a LIF output can also write to memory for display
+	 * writeback.
+	 */
+	if (vsp1->info->gen > 2 && index < vsp1->info->lif_count)
+		wpf->has_writeback = true;
+
 	wpf->entity.ops = &wpf_entity_ops;
 	wpf->entity.type = VSP1_ENTITY_WPF;
 	wpf->entity.index = index;

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