drm: xlnx: zynqmp_dpsub: Enable plane in atomic update

Unconditionally enable the DPSUB layer in the corresponding atomic plane
update callback. Setting the new display mode may require disabling and
re-enabling the CRTC. This effectively resets DPSUB to the default state
with all layers disabled. The original implementation of the plane atomic
update enables the corresponding DPSUB layer only if the framebuffer
format has changed. This would leave the layer disabled after switching to
a different display mode with the same framebuffer format.
Signed-off-by: Anatoliy Klymenko <anatoliy.klymenko@amd.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240523-dp-layer-enable-v2-1-d799020098fc@amd.com

drivers/gpu/drm/xlnx/zynqmp_kms.c

@@ -120,8 +120,12 @@ static void zynqmp_dpsub_plane_atomic_update(struct drm_plane *plane,
 		zynqmp_disp_blend_set_global_alpha(dpsub->disp, true,
 						   plane->state->alpha >> 8);
 
-	/* Enable or re-enable the plane if the format has changed. */
-	if (format_changed)
+	/*
+	 * Unconditionally enable the layer, as it may have been disabled
+	 * previously either explicitly to reconfigure layer format, or
+	 * implicitly after DPSUB reset during display mode change. DRM
+	 * framework calls this callback for enabled planes only.
+	 */
 	zynqmp_disp_layer_enable(layer);
 }