[PATCH] drm/pl111: Advertise no pixel blending

[Roshan Kumar]

Commit 860e748bddcc ("drm: ensure blend mode supported if
pixel format with alpha exposed") added validation that warns when a
plane exposes an alpha format without a pixel blend mode property. PL111
exposes several such formats but does not attach the property.

The PL110/PL111 controller scans out a single framebuffer and does not
blend its alpha channel with a background. Advertise
DRM_MODE_BLEND_PIXEL_NONE to match the existing hardware behavior.

With panic_on_warn enabled, this warning prevents the syzkaller
vexpress-a15 manager from booting. The change was tested on current
master with QEMU 10 and the existing production DTB; the guest reached
sshd and returned an SSH banner.

Fixes: 860e748bddcc ("drm: ensure blend mode supported if pixel format with alpha exposed")
Link: https://github.com/google/syzkaller/issues/7805
Signed-off-by: Roshan Kumar <roshaen09@xxxxxxxxx>
---
 drivers/gpu/drm/pl111/pl111_display.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/pl111/pl111_display.c b/drivers/gpu/drm/pl111/pl111_display.c
index 5d10bc5..758b297 100644
--- a/drivers/gpu/drm/pl111/pl111_display.c
+++ b/drivers/gpu/drm/pl111/pl111_display.c
@@ -15,6 +15,7 @@
 #include <linux/media-bus-format.h>
 #include <linux/of_graph.h>
 
+#include <drm/drm_blend.h>
 #include <drm/drm_fb_dma_helper.h>
 #include <drm/drm_fourcc.h>
 #include <drm/drm_framebuffer.h>
@@ -596,5 +597,10 @@ int pl111_display_init(struct drm_device *drm)
 	if (ret)
 		return ret;
 
+	ret = drm_plane_create_blend_mode_property(&priv->pipe.plane,
+						   BIT(DRM_MODE_BLEND_PIXEL_NONE));
+	if (ret)
+		return ret;
+
 	return 0;
 }
-- 
2.43.0