drm: apple: warn about broken sw cursor fallback

Some userspace may not handle invalid plane checks gracefully
when falling back to a software cursor. This will manifest
as the screen freezing, recoverable by moving the cursor away
from a screen edge. Throw a warning once to let the user know
why this has happened.

Signed-off-by: James Calligeros <jcalligeros99@gmail.com>

Author: chadmed

drivers/gpu/drm/apple/apple_drv.c

@@ -101,6 +101,18 @@ static int apple_plane_atomic_check(struct drm_plane *plane,
 	 */
 	if ((new_plane_state->crtc_x + 32) > crtc_state->mode.hdisplay ||
 	     (new_plane_state->crtc_y + 32) > crtc_state->mode.vdisplay) {
+		dev_err_once(state->dev->dev,
+			"Plane operation would have crashed DCP! Rejected!\n\
+			DCP requires 32x32 of every plane to be within screen space.\n\
+			Your compositor asked for a screen space area of [%d, %d].\n\
+			This is not supported, and your compositor should have\n\
+			switched to software compositing when this operation failed.\n\
+			You should not have noticed this at all. If your screen\n\
+			froze/hitched, or your compositor crashed, please report\n\
+			this to the your compositor's developers. We will not\n\
+			throw this error again until you next reboot.\n",
+			crtc_state->mode.hdisplay - new_plane_state->crtc_x,
+			crtc_state->mode.vdisplay - new_plane_state->crtc_y);
 		return -EINVAL;
 	}