drm/i915: Prevent HW access during init from connector get_modes hooks

Prevent accessing the HW from the get_modes hooks of connectors deriving
the mode list from the display's EDID. drm_edid_connector_add_modes()
will return the mode list based on the EDID which was cached during a
previous detection/get_modes call.

This also fixes the NULL deref problem (10085) which was
introduced/revealed by

commit bab87ef4db9a ("drm/i915: Disable hotplug detection handlers during driver init/shutdown")

After the above change MST connectors will not change state during
driver init/shutdown; thus some of these connectors with no I2C/DDC
adapter registered for them (since the given MST port has no sink
connected) may stay then in the 'unknown' connector status. The
get_modes() hook should not try to use the I2C/DDC adapter in this state
(which would lead to the above NULL deref) which this patch ensures.

v2:
- Remove the redundant check from intel_crt_ddc_get_modes().
- Rebase on latest drm-tip.
- Add Fixes: line / related commit notes.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/10085
Fixes: bab87ef4db9a ("drm/i915: Disable hotplug detection handlers during driver init/shutdown")
Signed-off-by: Imre Deak <[email protected]>
Reviewed-by: Jouni Högander <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 5fa25a5a36b5..5307ddd4edcf 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -1197,6 +1197,7 @@ static bool intel_dp_mst_initial_fastset_check(struct intel_encoder *encoder,
 static int intel_dp_mst_get_ddc_modes(struct drm_connector *connector)
 {
 	struct intel_connector *intel_connector = to_intel_connector(connector);
+	struct drm_i915_private *i915 = to_i915(intel_connector->base.dev);
 	struct intel_dp *intel_dp = intel_connector->mst_port;
 	const struct drm_edid *drm_edid;
 	int ret;
@@ -1204,6 +1205,9 @@ static int intel_dp_mst_get_ddc_modes(struct drm_connector *connector)
 	if (drm_connector_is_unregistered(connector))
 		return intel_connector_update_modes(connector, NULL);
 
+	if (!intel_display_driver_check_access(i915))
+		return drm_edid_connector_add_modes(connector);
+
 	drm_edid = drm_dp_mst_edid_read(connector, &intel_dp->mst_mgr, intel_connector->port);
 
 	ret = intel_connector_update_modes(connector, drm_edid);