[PATCH] drm/amd/display: Do not reset planes based on crtc zpos_changed

[Harry Wentland]

On 2024-09-06 17:20, sunpeng.li at amd.com wrote:
> From: Leo Li <sunpeng.li at amd.com>
> 
> [Why]
> 
> drm_normalize_zpos will set the crtc_state->zpos_changed to 1 if any of
> it's assigned planes changes zpos, or is removed/added from it.
> 
> To have amdgpu_dm request a plane reset on this is too broad. For
> example, if only the cursor plane was moved from one crtc to another,
> the crtc's zpos_changed will be set to true. But that does not mean that
> the underlying primary plane requires a reset.
> 
> [How]
> 
> Narrow it down so that only the plane that has a change in zpos will
> require a reset.
> 
> As a future TODO, we can further optimize this by only requiring a reset
> on z-order change. Z-order is different from z-pos, since a zpos change
> doesn't necessarily mean the z-ordering changed, and DC should only
> require a reset if the z-ordering changed.
> 
> For example, the following zpos update does not change z-ordering:
> 
>     Plane A: zpos 2 -> 3
>     Plane B: zpos 1 -> 2
>     => Plane A is still on top of plane B: no reset needed
> 
> Whereas this one does change z-ordering:
> 
>     Plane A: zpos 2 -> 1
>     Plane B: zpos 1 -> 2
>     => Plane A changed from on top, to below plane B: reset needed
> 
> Fixes: 38e0c3df6dbd ("drm/amd/display: Move PRIMARY plane zpos higher")
> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3569
> Signed-off-by: Leo Li <sunpeng.li at amd.com>

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

Harry

> ---
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> 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 43bf8883ddc0f..a3edaf658ae00 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -10579,7 +10579,7 @@ static bool should_reset_plane(struct drm_atomic_state *state,
>  	 * TODO: We can likely skip bandwidth validation if the only thing that
>  	 * changed about the plane was it'z z-ordering.
>  	 */
> -	if (new_crtc_state->zpos_changed)
> +	if (old_plane_state->normalized_zpos != new_plane_state->normalized_zpos)
>  		return true;
>  
>  	if (drm_atomic_crtc_needs_modeset(new_crtc_state))