Re: [PATCH] amd/display: only accept async flips for fast updates

[Harry Wentland <harry.wentland@amd.com>]

On 2023-06-21 16:24, André Almeida wrote:
> From: Simon Ser <contact@emersion.fr>
> 
> Up until now, amdgpu was silently degrading to vsync when
> user-space requested an async flip but the hardware didn't support
> it.
> 
> The hardware doesn't support immediate flips when the update changes
> the FB pitch, the DCC state, the rotation, enables or disables CRTCs
> or planes, etc. This is reflected in the dm_crtc_state.update_type
> field: UPDATE_TYPE_FAST means that immediate flip is supported.
> 
> Silently degrading async flips to vsync is not the expected behavior
> from a uAPI point-of-view. Xorg expects async flips to fail if
> unsupported, to be able to fall back to a blit. i915 already behaves
> this way.
> 
> This patch aligns amdgpu with uAPI expectations and returns a failure
> when an async flip is not possible.
> 
> Signed-off-by: Simon Ser <contact@emersion.fr>
> Reviewed-by: André Almeida <andrealmeid@igalia.com>
> Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
> Signed-off-by: André Almeida <andrealmeid@igalia.com>

Reviewed-by: Harry Wentland <harry.wentland@amd.com>

Harry

> ---
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c    |  8 ++++++++
>  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c   | 12 ++++++++++++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index 514f6785a020..1d9b84e5835f 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -8136,7 +8136,15 @@ static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
>  		 * Only allow immediate flips for fast updates that don't
>  		 * change memory domain, FB pitch, DCC state, rotation or
>  		 * mirroring.
> +		 *
> +		 * dm_crtc_helper_atomic_check() only accepts async flips with
> +		 * fast updates.
>  		 */
> +		if (crtc->state->async_flip &&
> +		    acrtc_state->update_type != UPDATE_TYPE_FAST)
> +			drm_warn_once(state->dev,
> +				      "[PLANE:%d:%s] async flip with non-fast update\n",
> +				      plane->base.id, plane->name);
>  		bundle->flip_addrs[planes_count].flip_immediate =
>  			crtc->state->async_flip &&
>  			acrtc_state->update_type == UPDATE_TYPE_FAST &&
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
> index 440fc0869a34..30d4c6fd95f5 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
> @@ -398,6 +398,18 @@ static int dm_crtc_helper_atomic_check(struct drm_crtc *crtc,
>  		return -EINVAL;
>  	}
>  
> +	/*
> +	 * Only allow async flips for fast updates that don't change the FB
> +	 * pitch, the DCC state, rotation, etc.
> +	 */
> +	if (crtc_state->async_flip &&
> +	    dm_crtc_state->update_type != UPDATE_TYPE_FAST) {
> +		drm_dbg_atomic(crtc->dev,
> +			       "[CRTC:%d:%s] async flips are only supported for fast updates\n",
> +			       crtc->base.id, crtc->name);
> +		return -EINVAL;
> +	}
> +
>  	/* In some use cases, like reset, no stream is attached */
>  	if (!dm_crtc_state->stream)
>  		return 0;