[PATCH 5/9] drm/i915/intel_i2c: add locking around i2c algorithm accesses

[Daniel Kurtz]

The i915 has multiple i2c adapters.  However, they all share a single
single set of i2c control registers (algorithm).  Thus, different threads
trying to access different adapters could interfere with each other.

Note: different threads trying to access the same channel is already
handled in the i2c-core using the i2c adapter lock.

This patch adds a mutex to serialize access to the gmbus_xfer routine.
Note: the same mutex serializes both bit banged and native xfers.

Signed-off-by: Yufeng Shen <miletus at chromium.org>
Signed-off-by: Daniel Kurtz <djkurtz at chromium.org>
---
 drivers/gpu/drm/i915/i915_drv.h  |    1 +
 drivers/gpu/drm/i915/intel_i2c.c |   12 ++++++++++++
 2 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 64d1276..c7f0809 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -301,6 +301,7 @@ typedef struct drm_i915_private {
 		struct i2c_adapter *force_bit;
 		u32 reg0;
 	} *gmbus;
+	struct mutex gmbus_mutex;
 
 	struct pci_dev *bridge_dev;
 	struct intel_ring_buffer ring[I915_NUM_RINGS];
diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index b2cc7f2..b97392c 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -213,6 +213,8 @@ intel_i2c_quirk_xfer(struct drm_i915_private *dev_priv,
 					       adapter);
 	int ret;
 
+	mutex_lock(&dev_priv->gmbus_mutex);
+
 	intel_i2c_reset(dev_priv->dev);
 
 	intel_i2c_quirk_set(dev_priv, true);
@@ -226,6 +228,8 @@ intel_i2c_quirk_xfer(struct drm_i915_private *dev_priv,
 	set_clock(gpio, 1);
 	intel_i2c_quirk_set(dev_priv, false);
 
+	mutex_unlock(&dev_priv->gmbus_mutex);
+
 	return ret;
 }
 
@@ -244,6 +248,7 @@ gmbus_xfer(struct i2c_adapter *adapter,
 		return intel_i2c_quirk_xfer(dev_priv, bus->force_bit, msgs,
 					    num);
 
+	mutex_lock(&dev_priv->gmbus_mutex);
 
 	reg_offset = HAS_PCH_SPLIT(dev_priv->dev) ? PCH_GMBUS0 - GMBUS0 : 0;
 
@@ -334,6 +339,9 @@ 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:
@@ -341,6 +349,8 @@ timeout:
 		 bus->reg0 & 0xff, bus->adapter.name);
 	I915_WRITE(GMBUS0 + reg_offset, 0);
 
+	mutex_unlock(&dev_priv->gmbus_mutex);
+
 	/* 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)
@@ -383,6 +393,8 @@ 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 < ARRAY_SIZE(gmbus_ports); i++) {
 		struct intel_gmbus *bus = &dev_priv->gmbus[i];
 		int port = i + 1; /* +1 to map gmbus index to pin pair */
-- 
1.7.7.3