drm/i915: Fix race condition in accessing GMBUS

GMBUS has several ports and each has it's own corresponding
I2C adpater. When multiple I2C adapters call gmbus_xfer() at
the same time there is a race condition in using the underlying
GMBUS controller. Fixing this by adding a mutex lock when calling
gmbus_xfer().

v2: Moved gmbus_mutex below intel_gmbus and added comments.
Rebased to drm-intel-next-queued.

Signed-off-by: Yufeng Shen <miletus@chromium.org>
[danvet: Shortened the gmbus_mutex comment a bit and add the patch
revision comment to the commit message.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index caec1fdb7dda..8e3eb5e282a1 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -313,6 +313,10 @@ typedef struct drm_i915_private {
                 u32 reg0;
         } *gmbus;
 
+        /** gmbus_mutex protects against concurrent usage of the single hw gmbus
+         * controller on different i2c buses. */
+        struct mutex gmbus_mutex;
+
         struct pci_dev *bridge_dev;
         struct intel_ring_buffer ring[I915_NUM_RINGS];
         uint32_t next_seqno;