Re: [PATCH] drm/vram-helpers: Set plane fence for display update

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Mar 31, 2020 at 10:11:30AM +0200, Thomas Zimmermann wrote:
> Calling the VRAM helper's prepare_fb() helper now sets the plane's
> fence object. The helper still has to synchronize with other users
> of the GEM object. Leave a related TODO comment in the code.
> 
> This will be useful for PRIME support. VRAM helpers don't support
> buffer sharing ATM, so there are no drivers requiring this change.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
>  drivers/gpu/drm/drm_gem_vram_helper.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
> index b3201a70cbfcb..d4e4f80d3a6c1 100644
> --- a/drivers/gpu/drm/drm_gem_vram_helper.c
> +++ b/drivers/gpu/drm/drm_gem_vram_helper.c
> @@ -5,6 +5,7 @@
>  #include <drm/drm_drv.h>
>  #include <drm/drm_file.h>
>  #include <drm/drm_framebuffer.h>
> +#include <drm/drm_gem_framebuffer_helper.h>
>  #include <drm/drm_gem_ttm_helper.h>
>  #include <drm/drm_gem_vram_helper.h>
>  #include <drm/drm_mode.h>
> @@ -670,9 +671,9 @@ EXPORT_SYMBOL(drm_gem_vram_driver_dumb_mmap_offset);
>   * @plane:	a DRM plane
>   * @new_state:	the plane's new state
>   *
> - * During plane updates, this function pins the GEM VRAM
> - * objects of the plane's new framebuffer to VRAM. Call
> - * drm_gem_vram_plane_helper_cleanup_fb() to unpin them.
> + * During plane updates, this function sets the plane's fence and
> + * pins the GEM VRAM objects of the plane's new framebuffer to VRAM.
> + * Call drm_gem_vram_plane_helper_cleanup_fb() to unpin them.
>   *
>   * Returns:
>   *	0 on success, or
> @@ -689,6 +690,13 @@ drm_gem_vram_plane_helper_prepare_fb(struct drm_plane *plane,
>  	if (!new_state->fb)
>  		return 0;
>  
> +	/*
> +	 * TODO: Synchronize with other users of the buffer. Buffers
> +	 *       cannot be pinned to VRAM while they are in use by other
> +	 *       drivers for DMA. We should probably wait for each GEM
> +	 *       object's fence before attempting to pin the buffer.
> +	 *       There are currently no users of this functionality.
> +	 */

Not sure this is warranted, we have lots of drivers with these kind of
restrictions ... It's a big can of worms, I'd just leave this all out.

>  	for (i = 0; i < ARRAY_SIZE(new_state->fb->obj); ++i) {
>  		if (!new_state->fb->obj[i])
>  			continue;
> @@ -698,6 +706,10 @@ drm_gem_vram_plane_helper_prepare_fb(struct drm_plane *plane,
>  			goto err_drm_gem_vram_unpin;
>  	}
>  
> +	ret = drm_gem_fb_prepare_fb(plane, new_state);
> +	if (ret)
> +		goto err_drm_gem_vram_unpin;

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> +
>  	return 0;
>  
>  err_drm_gem_vram_unpin:
> -- 
> 2.26.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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