[PATCH v1] drm: Do not allow to set NOFB for active primary plane

[Ville Syrjälä]

On Mon, Apr 15, 2019 at 10:58:47AM +0300, Stanislav Lisovskiy wrote:
> There was an issue reported from end users, confirmed
> also locally that when user executes xrandr --output <some DP>
> --rotate left/right, the other eDP screen gets blank after rotation.
> 
> Investigation showed that reason was that primary plane
> was that screen was for some reason disabled, while cursor
> plane was still enabled.
> After some effort it turns out that userspace might wrongly
> assign NOFB to active primary plane for some reason.
> 
> Then this gets detected in drm_atomic_helper_check_plane_state,
> called from ->plane_check and plane gets deactivated, leaving
> the screen blank and cursor visible. This can be cured by reboot
> or xrandr off/on sequence for that crtc.
> 
> This patch is proposal to fix the issue by forbiding fb removal
> from active primary plane. If one needs to remove fb plane must be
> disabled first.
> 
> Not sure if this is correct, however it fixes the issue at least.

It is not. Removing the fb (and crtc) is how you disable a plane.

> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110375
> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> ---
>  drivers/gpu/drm/drm_atomic_uapi.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
> index ea797d4c82ee..e2f078b302f3 100644
> --- a/drivers/gpu/drm/drm_atomic_uapi.c
> +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> @@ -229,6 +229,15 @@ drm_atomic_set_fb_for_plane(struct drm_plane_state *plane_state,
>  {
>  	struct drm_plane *plane = plane_state->plane;
>  
> +	if (!fb) {
> +		if (plane->state->visible && plane->type == DRM_PLANE_TYPE_PRIMARY) {a

.visible is not even computed yet when this is called.

> +			DRM_DEBUG_ATOMIC("Not allowed to set [NOFB] for active"
> +					" primary [PLANE:%d:%s] - disable first",
> +					plane->base.id, plane->name);
> +			return;
> +		}
> +	}
> +
>  	if (fb)
>  		DRM_DEBUG_ATOMIC("Set [FB:%d] for [PLANE:%d:%s] state %p\n",
>  				 fb->base.id, plane->base.id, plane->name,
> -- 
> 2.17.1
> 
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-- 
Ville Syrjälä
Intel