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 <imre.deak@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240212175237.2625812-2-imre.deak@intel.com

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_sdvo.c b/drivers/gpu/drm/i915/display/intel_sdvo.c
index eb65c8124e60..3b79488357ba 100644
--- a/drivers/gpu/drm/i915/display/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/display/intel_sdvo.c
@@ -2202,12 +2202,16 @@ intel_sdvo_detect(struct drm_connector *connector, bool force)
 
 static int intel_sdvo_get_ddc_modes(struct drm_connector *connector)
 {
+	struct drm_i915_private *i915 = to_i915(connector->dev);
 	int num_modes = 0;
 	const struct drm_edid *drm_edid;
 
 	drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s]\n",
 		    connector->base.id, connector->name);
 
+	if (!intel_display_driver_check_access(i915))
+		return drm_edid_connector_add_modes(connector);
+
 	/* set the bus switch and get the modes */
 	drm_edid = intel_sdvo_get_edid(connector);