[Intel-gfx] [PATCH] drm/i915: Do not create a new max_bpc prop for MST connectors

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

We're not allowed to create new properties after device registration
so for MST connectors we need to either create the max_bpc property
earlier, or we reuse one we already have. Let's do the latter apporach
since the corresponding SST connector already has the prop and its
min/max are correct also for the MST connector.

The problem was highlighted by commit 4f5368b5541a ("drm/kms:
Catch mode_object lifetime errors") which results in the following
spew:
[ 1330.878941] WARNING: CPU: 2 PID: 1554 at drivers/gpu/drm/drm_mode_object.c:45 __drm_mode_object_add+0xa0/0xb0 [drm]
...
[ 1330.879008] Call Trace:
[ 1330.879023]  drm_property_create+0xba/0x180 [drm]
[ 1330.879036]  drm_property_create_range+0x15/0x30 [drm]
[ 1330.879048]  drm_connector_attach_max_bpc_property+0x62/0x80 [drm]
[ 1330.879086]  intel_dp_add_mst_connector+0x11f/0x140 [i915]
[ 1330.879094]  drm_dp_add_port.isra.20+0x20b/0x440 [drm_kms_helper]
...

Cc: stable at vger.kernel.org
Cc: Lyude Paul <lyude at redhat.com>
Cc: sunpeng.li at amd.com
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Sean Paul <sean at poorly.run>
Fixes: 5ca0ef8a56b8 ("drm/i915: Add max_bpc property for DP MST")
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp_mst.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 83faa246e361..9748581c1d62 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -536,7 +536,15 @@ static struct drm_connector *intel_dp_add_mst_connector(struct drm_dp_mst_topolo
 
 	intel_attach_force_audio_property(connector);
 	intel_attach_broadcast_rgb_property(connector);
-	drm_connector_attach_max_bpc_property(connector, 6, 12);
+
+	/*
+	 * Reuse the prop from the SST connector because we're
+	 * not allowed to create new props after device registration.
+	 */
+	connector->max_bpc_property =
+		intel_dp->attached_connector->base.max_bpc_property;
+	if (connector->max_bpc_property)
+		drm_connector_attach_max_bpc_property(connector, 6, 12);
 
 	return connector;
 
-- 
2.21.0