Re: [PATCH v1 8/8] drm/i915/fbc: handle dirty rect coords for the first frame

["Govindapillai, Vinod" <vinod.govindapillai@intel.com>]

Hi Ville,

During some testing I noticed that for the very first frame while enabling we wouldnt have executed
the intel_fbc_prepare_dirty_rect() as fbc_state->plane will be NULL. So we will end-up programming
wrong values for the first frame. And for the very first frame after the boot it will be completely
bogus! Added this patch to the list and if you could Ack this, then I can squash this patch to the
fbc dirty rect patch (patch 6) in the list

Br
Vinod


On Sun, 2025-02-16 at 22:09 +0200, Vinod Govindapillai wrote:
> During enablig FBC, for the very first frame, the prepare dirty
> rect routine wouldnt have executed as at that time the plane
> reference in the fbc_state would be NULL. So this could make
> driver program some invalid entries as the damage area. Though
> fbc hw ignores the dirty rect values programmed for the first
> frame after enabling FBC, driver must ensure that valid dirty
> rect coords are programmed. So ensure that for the first frame
> prepare dirty rect is called at the time enabling FBC.
> 
> Signed-off-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_fbc.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c b/drivers/gpu/drm/i915/display/intel_fbc.c
> index 6222eea4b1ce..21fd57c7f163 100644
> --- a/drivers/gpu/drm/i915/display/intel_fbc.c
> +++ b/drivers/gpu/drm/i915/display/intel_fbc.c
> @@ -1230,6 +1230,8 @@ intel_fbc_dirty_rect_update(struct intel_dsb *dsb, struct intel_fbc *fbc)
>  
>  	lockdep_assert_held(&fbc->lock);
>  
> +	drm_WARN_ON(display->drm, fbc_dirty_rect->y2 == 0);
> +
>  	intel_de_write_dsb(display, dsb, XE3_FBC_DIRTY_RECT(fbc->id),
>  			   FBC_DIRTY_RECT_START_LINE(fbc_dirty_rect->y1) |
>  			   FBC_DIRTY_RECT_END_LINE(fbc_dirty_rect->y2 - 1));
> @@ -1313,6 +1315,13 @@ static void intel_fbc_update_state(struct intel_atomic_state *state,
>  	WARN_ON(plane_state->no_fbc_reason);
>  	WARN_ON(fbc_state->plane && fbc_state->plane != plane);
>  
> +	/*
> +	 * For the very first frame while enabling FBC, ensure that we have a
> +	 * valid dirty rect coords.
> +	 */
> +	if (HAS_FBC_DIRTY_RECT(display) && !fbc_state->plane)
> +		__intel_fbc_prepare_dirty_rect(plane_state);
> +
>  	fbc_state->plane = plane;
>  
>  	/* FBC1 compression interval: arbitrary choice of 1 second */