drm/i915: don't use uninitialized EDID bpc values when picking pipe bpp

The EDID parser will zero out the bpc value, and the driver needs to handle
that case.  In our picker, we'll just ignore 0 values as far as bpp
picking goes.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=39323.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Keith Packard <keithp@keithp.com>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 2bf5bb6..35364e6 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -4600,7 +4600,9 @@
 			if (connector->encoder != encoder)
 				continue;
 
-			if (connector->display_info.bpc < display_bpc) {
+			/* Don't use an invalid EDID bpc value */
+			if (connector->display_info.bpc &&
+			    connector->display_info.bpc < display_bpc) {
 				DRM_DEBUG_DRIVER("clamping display bpc (was %d) to EDID reported max of %d\n", display_bpc, connector->display_info.bpc);
 				display_bpc = connector->display_info.bpc;
 			}
@@ -5215,7 +5217,8 @@
 		temp |= PIPE_12BPC;
 		break;
 	default:
-		WARN(1, "intel_choose_pipe_bpp returned invalid value\n");
+		WARN(1, "intel_choose_pipe_bpp returned invalid value %d\n",
+			pipe_bpp);
 		temp |= PIPE_8BPC;
 		pipe_bpp = 24;
 		break;