drm/i915: duct-tape locking when eDP init fails

Thanks to apple gpu mux fail we detect an eDP output, but can't read
anything over dp aux. In the resulting failure path we then hit a
paranoid WARN about potential locking.

Since the WARN is pretty useful for normal operation just paper over
it in the failure case by grabbing the demanded (but for init/teardown
not really required) lock.

I've checked our driver unload code and we already don't hold the kms
lock when calling drm_mode_config_cleanup. So this won't lead to a new
deadlock when reloading i915.ko.

v2: Make it compile.

Reported-by: Dave Airlie <[email protected]>
Cc: Dave Airlie <[email protected]>
Reviewed-by: Jani Nikula <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index d7d4afe01341..8fc93f90a7cd 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -2559,12 +2559,15 @@ void intel_dp_encoder_destroy(struct drm_encoder *encoder)
 {
 	struct intel_digital_port *intel_dig_port = enc_to_dig_port(encoder);
 	struct intel_dp *intel_dp = &intel_dig_port->dp;
+	struct drm_device *dev = intel_dp_to_dev(intel_dp);
 
 	i2c_del_adapter(&intel_dp->adapter);
 	drm_encoder_cleanup(encoder);
 	if (is_edp(intel_dp)) {
 		cancel_delayed_work_sync(&intel_dp->panel_vdd_work);
+		mutex_lock(&dev->mode_config.mutex);
 		ironlake_panel_vdd_off_sync(intel_dp);
+		mutex_unlock(&dev->mode_config.mutex);
 	}
 	kfree(intel_dig_port);
 }