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Subject[PATCH] drm/i915: Fix race condition in accessing GMBUS
Date
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().

Signed-off-by: Yufeng Shen <miletus@chromium.org>
---
drivers/gpu/drm/i915/i915_drv.h | 2 ++
drivers/gpu/drm/i915/intel_i2c.c | 21 ++++++++++++++++-----
2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 9689ca3..d0f826e 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -733,6 +733,8 @@ typedef struct drm_i915_private {
u8 corr;
spinlock_t *mchdev_lock;

+ struct mutex gmbus_mutex;
+
enum no_fbc_reason no_fbc_reason;

struct drm_mm_node *compressed_fb;
diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index d30cccc..24fafdc 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -233,11 +233,16 @@ gmbus_xfer(struct i2c_adapter *adapter,
struct intel_gmbus,
adapter);
struct drm_i915_private *dev_priv = adapter->algo_data;
- int i, reg_offset;
+ int i, reg_offset, ret;

- if (bus->force_bit)
- return intel_i2c_quirk_xfer(dev_priv,
+ mutex_lock(&dev_priv->gmbus_mutex);
+
+ if (bus->force_bit) {
+ ret = intel_i2c_quirk_xfer(dev_priv,
bus->force_bit, msgs, num);
+ mutex_unlock(&dev_priv->gmbus_mutex);
+ return ret;
+ }

reg_offset = HAS_PCH_SPLIT(dev_priv->dev) ? PCH_GMBUS0 - GMBUS0 : 0;

@@ -321,6 +326,7 @@ done:
* start of the next xfer, till then let it sleep.
*/
I915_WRITE(GMBUS0 + reg_offset, 0);
+ mutex_unlock(&dev_priv->gmbus_mutex);
return i;

timeout:
@@ -331,9 +337,12 @@ timeout:
/* Hardware may not support GMBUS over these pins? Try GPIO bitbanging instead. */
bus->force_bit = intel_gpio_create(dev_priv, bus->reg0 & 0xff);
if (!bus->force_bit)
- return -ENOMEM;
+ ret = -ENOMEM;
+ else
+ ret = intel_i2c_quirk_xfer(dev_priv, bus->force_bit, msgs, num);

- return intel_i2c_quirk_xfer(dev_priv, bus->force_bit, msgs, num);
+ mutex_unlock(&dev_priv->gmbus_mutex);
+ return ret;
}

static u32 gmbus_func(struct i2c_adapter *adapter)
@@ -380,6 +389,8 @@ int intel_setup_gmbus(struct drm_device *dev)
if (dev_priv->gmbus == NULL)
return -ENOMEM;

+ mutex_init(&dev_priv->gmbus_mutex);
+
for (i = 0; i < GMBUS_NUM_PORTS; i++) {
struct intel_gmbus *bus = &dev_priv->gmbus[i];

--
1.7.3.1


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