Re: [PATCH v5 5/9] drm: vkms: Add fb information to `vkms_writeback_job`

[Pekka Paalanen <ppaalanen@gmail.com>]

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On Mon,  4 Apr 2022 17:45:11 -0300
Igor Torrente <igormtorrente@gmail.com> wrote:

> This commit is the groundwork to introduce new formats to the planes and
> writeback buffer. As part of it, a new buffer metadata field is added to
> `vkms_writeback_job`, this metadata is represented by the `vkms_composer`
> struct.

Hi,

should this be talking about vkms_frame_info struct instead?

> 
> Also adds two new function pointers (`{wb,plane}_format_transform_func`)
> are defined to handle format conversion to/from internal format.
> 
> These things will allow us, in the future, to have different compositing
> and wb format types.
> 
> V2: Change the code to get the drm_framebuffer reference and not copy its
>     contents(Thomas Zimmermann).
> V3: Drop the refcount in the wb code(Thomas Zimmermann).
> V5: Add {wb,plane}_format_transform_func to vkms_writeback_job
>     and vkms_plane_state (Pekka Paalanen)
> 
> Signed-off-by: Igor Torrente <igormtorrente@gmail.com>
> ---
>  drivers/gpu/drm/vkms/vkms_composer.c  |  4 ++--
>  drivers/gpu/drm/vkms/vkms_drv.h       | 31 +++++++++++++++++++++------
>  drivers/gpu/drm/vkms/vkms_plane.c     | 10 ++++-----
>  drivers/gpu/drm/vkms/vkms_writeback.c | 20 ++++++++++++++---
>  4 files changed, 49 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> index 2d946368a561..95029d2ebcac 100644
> --- a/drivers/gpu/drm/vkms/vkms_composer.c
> +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> @@ -153,7 +153,7 @@ static void compose_plane(struct vkms_frame_info *primary_plane_info,
>  			  struct vkms_frame_info *plane_frame_info,
>  			  void *vaddr_out)
>  {
> -	struct drm_framebuffer *fb = &plane_frame_info->fb;
> +	struct drm_framebuffer *fb = plane_frame_info->fb;
>  	void *vaddr;
>  	void (*pixel_blend)(const u8 *p_src, u8 *p_dst);
>  
> @@ -175,7 +175,7 @@ static int compose_active_planes(void **vaddr_out,
>  				 struct vkms_frame_info *primary_plane_info,
>  				 struct vkms_crtc_state *crtc_state)
>  {
> -	struct drm_framebuffer *fb = &primary_plane_info->fb;
> +	struct drm_framebuffer *fb = primary_plane_info->fb;
>  	struct drm_gem_object *gem_obj = drm_gem_fb_get_obj(fb, 0);
>  	const void *vaddr;
>  	int i;
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index 2e6342164bef..2704cfb6904b 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -22,13 +22,8 @@
>  
>  #define NUM_OVERLAY_PLANES 8
>  
> -struct vkms_writeback_job {
> -	struct dma_buf_map map[DRM_FORMAT_MAX_PLANES];
> -	struct dma_buf_map data[DRM_FORMAT_MAX_PLANES];
> -};
> -
>  struct vkms_frame_info {
> -	struct drm_framebuffer fb;
> +	struct drm_framebuffer *fb;
>  	struct drm_rect src, dst;
>  	struct dma_buf_map map[DRM_FORMAT_MAX_PLANES];
>  	unsigned int offset;
> @@ -36,6 +31,29 @@ struct vkms_frame_info {
>  	unsigned int cpp;
>  };
>  
> +struct pixel_argb_u16 {
> +	u16 a, r, g, b;
> +};
> +
> +struct line_buffer {
> +	size_t n_pixels;
> +	struct pixel_argb_u16 *pixels;
> +};
> +
> +typedef void
> +(*wb_format_transform_func)(struct vkms_frame_info *frame_info,
> +			    const struct line_buffer *buffer, int y);
> +
> +typedef void
> +(*plane_format_transform_func)(struct line_buffer *buffer,
> +			       const struct vkms_frame_info *frame_info, int y);

It wasn't immediately obvious to me in which direction these function
types work from their names. The arguments are not wb and plane but
vkms_frame_info and line_buffer in both. The implementations of these
functions would have nothing specific to a wb or a plane either, would
they?

What about naming them frame_to_line_func and line_to_frame_func?

> +
> +struct vkms_writeback_job {
> +	struct dma_buf_map data[DRM_FORMAT_MAX_PLANES];
> +	struct vkms_frame_info frame_info;

Which frame_info is this? Should the field be called wb_frame_info?

> +	wb_format_transform_func format_func;

line_to_frame_func wb_write;

perhaps? The type explains the general type of the function, and the
field name refers to what it is used for.

> +};
> +
>  /**
>   * vkms_plane_state - Driver specific plane state
>   * @base: base plane state
> @@ -44,6 +62,7 @@ struct vkms_frame_info {
>  struct vkms_plane_state {
>  	struct drm_shadow_plane_state base;
>  	struct vkms_frame_info *frame_info;
> +	plane_format_transform_func format_func;

Similarly here, maybe

frame_to_line_func plane_read;

perhaps?

>  };
>  
>  struct vkms_plane {
> diff --git a/drivers/gpu/drm/vkms/vkms_plane.c b/drivers/gpu/drm/vkms/vkms_plane.c
> index a56b0f76eddd..28752af0118c 100644
> --- a/drivers/gpu/drm/vkms/vkms_plane.c
> +++ b/drivers/gpu/drm/vkms/vkms_plane.c
> @@ -50,12 +50,12 @@ static void vkms_plane_destroy_state(struct drm_plane *plane,
>  	struct vkms_plane_state *vkms_state = to_vkms_plane_state(old_state);
>  	struct drm_crtc *crtc = vkms_state->base.base.crtc;
>  
> -	if (crtc) {
> +	if (crtc && vkms_state->frame_info->fb) {
>  		/* dropping the reference we acquired in
>  		 * vkms_primary_plane_update()
>  		 */
> -		if (drm_framebuffer_read_refcount(&vkms_state->frame_info->fb))
> -			drm_framebuffer_put(&vkms_state->frame_info->fb);
> +		if (drm_framebuffer_read_refcount(vkms_state->frame_info->fb))
> +			drm_framebuffer_put(vkms_state->frame_info->fb);
>  	}
>  
>  	kfree(vkms_state->frame_info);
> @@ -110,9 +110,9 @@ static void vkms_plane_atomic_update(struct drm_plane *plane,
>  	frame_info = vkms_plane_state->frame_info;
>  	memcpy(&frame_info->src, &new_state->src, sizeof(struct drm_rect));
>  	memcpy(&frame_info->dst, &new_state->dst, sizeof(struct drm_rect));
> -	memcpy(&frame_info->fb, fb, sizeof(struct drm_framebuffer));
> +	frame_info->fb = fb;

This change, replacing the memcpy with storing a pointer, seems to be
another major point of this patch. Should it be a separate patch?
It doesn't seem to fit with the current commit message.

I have no idea what kind of locking or referencing a drm_framebuffer
would need, and I suspect that would be easier to review if it was a
patch of its own.

>  	memcpy(&frame_info->map, &shadow_plane_state->data, sizeof(frame_info->map));
> -	drm_framebuffer_get(&frame_info->fb);
> +	drm_framebuffer_get(frame_info->fb);

Does drm_framebuffer_get() not return anything?

To me it would be more idiomatic to write something like

	frame_info->fb = drm_framebuffer_get(fb);

I don't know if that pattern is used in the kernel, but I use it in
userspace to emphasise that frame_info owns a new reference rather than
borrowing someone else's.


Thanks,
pq

>  	frame_info->offset = fb->offsets[0];
>  	frame_info->pitch = fb->pitches[0];
>  	frame_info->cpp = fb->format->cpp[0];
> diff --git a/drivers/gpu/drm/vkms/vkms_writeback.c b/drivers/gpu/drm/vkms/vkms_writeback.c
> index 746cb0abc6ec..ad4bb1fb37ca 100644
> --- a/drivers/gpu/drm/vkms/vkms_writeback.c
> +++ b/drivers/gpu/drm/vkms/vkms_writeback.c
> @@ -74,12 +74,15 @@ static int vkms_wb_prepare_job(struct drm_writeback_connector *wb_connector,
>  	if (!vkmsjob)
>  		return -ENOMEM;
>  
> -	ret = drm_gem_fb_vmap(job->fb, vkmsjob->map, vkmsjob->data);
> +	ret = drm_gem_fb_vmap(job->fb, vkmsjob->frame_info.map, vkmsjob->data);
>  	if (ret) {
>  		DRM_ERROR("vmap failed: %d\n", ret);
>  		goto err_kfree;
>  	}
>  
> +	vkmsjob->frame_info.fb = job->fb;
> +	drm_framebuffer_get(vkmsjob->frame_info.fb);
> +
>  	job->priv = vkmsjob;
>  
>  	return 0;
> @@ -98,7 +101,9 @@ static void vkms_wb_cleanup_job(struct drm_writeback_connector *connector,
>  	if (!job->fb)
>  		return;
>  
> -	drm_gem_fb_vunmap(job->fb, vkmsjob->map);
> +	drm_gem_fb_vunmap(job->fb, vkmsjob->frame_info.map);
> +
> +	drm_framebuffer_put(vkmsjob->frame_info.fb);
>  
>  	vkmsdev = drm_device_to_vkms_device(job->fb->dev);
>  	vkms_set_composer(&vkmsdev->output, false);
> @@ -115,14 +120,23 @@ static void vkms_wb_atomic_commit(struct drm_connector *conn,
>  	struct drm_writeback_connector *wb_conn = &output->wb_connector;
>  	struct drm_connector_state *conn_state = wb_conn->base.state;
>  	struct vkms_crtc_state *crtc_state = output->composer_state;
> +	struct drm_framebuffer *fb = connector_state->writeback_job->fb;
> +	struct vkms_writeback_job *active_wb;
> +	struct vkms_frame_info *wb_frame_info;
>  
>  	if (!conn_state)
>  		return;
>  
>  	vkms_set_composer(&vkmsdev->output, true);
>  
> +	active_wb = conn_state->writeback_job->priv;
> +	wb_frame_info = &active_wb->frame_info;
> +
>  	spin_lock_irq(&output->composer_lock);
> -	crtc_state->active_writeback = conn_state->writeback_job->priv;
> +	crtc_state->active_writeback = active_wb;
> +	wb_frame_info->offset = fb->offsets[0];
> +	wb_frame_info->pitch = fb->pitches[0];
> +	wb_frame_info->cpp = fb->format->cpp[0];
>  	crtc_state->wb_pending = true;
>  	spin_unlock_irq(&output->composer_lock);
>  	drm_writeback_queue_job(wb_conn, connector_state);


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