drm/i915: Fix intel_atomic_setup_scalers() plane_state handling

Since the plane_state variable is declared outside the scaler_users
loop in intel_atomic_setup_scalers(), and it's never reset back to
NULL inside the loop we may end up calling intel_atomic_setup_scaler()
with a non-NULL plane state for the pipe scaling case. That is bad
because intel_atomic_setup_scaler() determines whether we are doing
plane scaling or pipe scaling based on plane_state!=NULL. The end
result is that we may miscalculate the scaler mode for pipe scaling.

The hardware becomes somewhat upset if we end up in this situation
when scanning out a planar format on a SDR plane. We end up
programming the pipe scaler into planar mode as well, and the
result is a screenfull of garbage.

Fix the situation by making sure we pass the correct plane_state==NULL
when calculating the scaler mode for pipe scaling.

Cc: stable@vger.kernel.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231207193441.20206-2-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>
(cherry picked from commit e8114410)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/display/skl_scaler.c

@@ -504,7 +504,6 @@ int intel_atomic_setup_scalers(struct drm_i915_private *dev_priv,
 {
 	struct drm_plane *plane = NULL;
 	struct intel_plane *intel_plane;
-	struct intel_plane_state *plane_state = NULL;
 	struct intel_crtc_scaler_state *scaler_state =
 		&crtc_state->scaler_state;
 	struct drm_atomic_state *drm_state = crtc_state->uapi.state;
@@ -536,6 +535,7 @@ int intel_atomic_setup_scalers(struct drm_i915_private *dev_priv,
 
 	/* walkthrough scaler_users bits and start assigning scalers */
 	for (i = 0; i < sizeof(scaler_state->scaler_users) * 8; i++) {
+		struct intel_plane_state *plane_state = NULL;
 		int *scaler_id;
 		const char *name;
 		int idx, ret;