Re: [Intel-gfx] [PATCH] drm/i915: Use vblank worker to unpin old legacy cursor fb safely

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Hey,


Den 2023-08-31 kl. 18:26, skrev Ville Syrjala:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> The cursor hardware only does sync updates, and thus the hardware
> will be scanning out from the old fb until the next start of vblank.
> So in order to make the legacy cursor fastpath actually safe we
> should not unpin the old fb until we're sure the hardware has
> ceased accessing it. The simplest approach is to just use a vblank
> work here to do the delayed unpin.
>
> Not 100% sure it's a good idea to put this onto the same high
> priority vblank worker as eg. our timing critical gamma updates.
> But let's keep it simple for now, and it we later discover that
> this is causing problems we can think about adding a lower
> priority worker for such things.
>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>   drivers/gpu/drm/i915/display/intel_cursor.c   | 25 +++++++++++++++++--
>   .../drm/i915/display/intel_display_types.h    |  3 +++
>   2 files changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_cursor.c b/drivers/gpu/drm/i915/display/intel_cursor.c
> index b342fad180ca..2bd1a79c6955 100644
> --- a/drivers/gpu/drm/i915/display/intel_cursor.c
> +++ b/drivers/gpu/drm/i915/display/intel_cursor.c
> @@ -603,6 +603,16 @@ static bool intel_cursor_format_mod_supported(struct drm_plane *_plane,
>   	return format == DRM_FORMAT_ARGB8888;
>   }
>   
> +static void intel_cursor_unpin_work(struct kthread_work *base)
> +{
> +	struct drm_vblank_work *work = to_drm_vblank_work(base);
> +	struct intel_plane_state *plane_state =
> +		container_of(work, typeof(*plane_state), unpin_work);
> +
> +	intel_plane_unpin_fb(plane_state);
> +	intel_plane_destroy_state(plane_state->uapi.plane, &plane_state->uapi);
> +}
> +
>   static int
>   intel_legacy_cursor_update(struct drm_plane *_plane,
>   			   struct drm_crtc *_crtc,
> @@ -730,14 +740,25 @@ intel_legacy_cursor_update(struct drm_plane *_plane,
>   
>   	local_irq_enable();
>   
> -	intel_plane_unpin_fb(old_plane_state);
> +	if (old_plane_state->hw.fb != new_plane_state->hw.fb) {
> +		drm_vblank_work_init(&old_plane_state->unpin_work, &crtc->base,
> +				     intel_cursor_unpin_work);
> +
> +		drm_vblank_work_schedule(&old_plane_state->unpin_work,
> +					 drm_crtc_accurate_vblank_count(&crtc->base) + 1,
> +					 false);
> +
> +		old_plane_state = NULL;
> +	} else {
> +		intel_plane_unpin_fb(old_plane_state);
> +	}

Maybe check if crtc is active and no modeset is happening? Similar to 
how the vblank worker is used in other cases. That should hopefully fix 
the cursor leak test.

Cheers,

~Maarten