drm/i915: Rework sdvo proxy i2c locking

lockdep complaints about a locking recursion for the i2c bus lock
because both the sdvo ddc proxy bus and the gmbus nested within use
the same locking class. It's not really a deadlock since we never nest
the other way round, but it's annoying.

Fix it by pulling the gmbus locking into the i2c lock_ops for both
i2c_adapater and making sure that the ddc_proxy_xfer function is
entirely lockless.

Re-layouting the extracted function resulted in some whitespace
cleanups, I figured we might as well keep them.

v2: Review from Chris:
- s/locked/unlocked/ since I got the naming backwards
- Use the vfuncs of the proxied adatper instead of re-rolling copies.
  That's more consistent with the other proxying we're doing.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170726132647.31833-1-daniel.vetter@ffwll.ch

drivers/gpu/drm/i915/intel_i2c.c

@@ -592,7 +592,6 @@ gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
 	int ret;
 
 	intel_display_power_get(dev_priv, POWER_DOMAIN_GMBUS);
-	mutex_lock(&dev_priv->gmbus_mutex);
 
 	if (bus->force_bit) {
 		ret = i2c_bit_algo.master_xfer(adapter, msgs, num);
@@ -604,7 +603,6 @@ gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
 			bus->force_bit |= GMBUS_FORCE_BIT_RETRY;
 	}
 
-	mutex_unlock(&dev_priv->gmbus_mutex);
 	intel_display_power_put(dev_priv, POWER_DOMAIN_GMBUS);
 
 	return ret;
@@ -624,6 +622,39 @@ static const struct i2c_algorithm gmbus_algorithm = {
 	.functionality	= gmbus_func
 };
 
+static void gmbus_lock_bus(struct i2c_adapter *adapter,
+			   unsigned int flags)
+{
+	struct intel_gmbus *bus = to_intel_gmbus(adapter);
+	struct drm_i915_private *dev_priv = bus->dev_priv;
+
+	mutex_lock(&dev_priv->gmbus_mutex);
+}
+
+static int gmbus_trylock_bus(struct i2c_adapter *adapter,
+			     unsigned int flags)
+{
+	struct intel_gmbus *bus = to_intel_gmbus(adapter);
+	struct drm_i915_private *dev_priv = bus->dev_priv;
+
+	return mutex_trylock(&dev_priv->gmbus_mutex);
+}
+
+static void gmbus_unlock_bus(struct i2c_adapter *adapter,
+			     unsigned int flags)
+{
+	struct intel_gmbus *bus = to_intel_gmbus(adapter);
+	struct drm_i915_private *dev_priv = bus->dev_priv;
+
+	mutex_unlock(&dev_priv->gmbus_mutex);
+}
+
+const struct i2c_lock_operations gmbus_lock_ops = {
+	.lock_bus =    gmbus_lock_bus,
+	.trylock_bus = gmbus_trylock_bus,
+	.unlock_bus =  gmbus_unlock_bus,
+};
+
 /**
  * intel_gmbus_setup - instantiate all Intel i2c GMBuses
  * @dev_priv: i915 device private
@@ -665,6 +696,7 @@ int intel_setup_gmbus(struct drm_i915_private *dev_priv)
 		bus->dev_priv = dev_priv;
 
 		bus->adapter.algo = &gmbus_algorithm;
+		bus->adapter.lock_ops = &gmbus_lock_ops;
 
 		/*
 		 * We wish to retry with bit banging

drivers/gpu/drm/i915/intel_sdvo.c

@@ -451,8 +451,9 @@ static const char * const cmd_status_names[] = {
 	"Scaling not supported"
 };
 
-static bool intel_sdvo_write_cmd(struct intel_sdvo *intel_sdvo, u8 cmd,
-				 const void *args, int args_len)
+static bool __intel_sdvo_write_cmd(struct intel_sdvo *intel_sdvo, u8 cmd,
+				   const void *args, int args_len,
+				   bool unlocked)
 {
 	u8 *buf, status;
 	struct i2c_msg *msgs;
@@ -498,7 +499,10 @@ static bool intel_sdvo_write_cmd(struct intel_sdvo *intel_sdvo, u8 cmd,
 	msgs[i+2].len = 1;
 	msgs[i+2].buf = &status;
 
+	if (unlocked)
 		ret = i2c_transfer(intel_sdvo->i2c, msgs, i+3);
+	else
+		ret = __i2c_transfer(intel_sdvo->i2c, msgs, i+3);
 	if (ret < 0) {
 		DRM_DEBUG_KMS("I2c transfer returned %d\n", ret);
 		ret = false;
@@ -516,6 +520,12 @@ static bool intel_sdvo_write_cmd(struct intel_sdvo *intel_sdvo, u8 cmd,
 	return ret;
 }
 
+static bool intel_sdvo_write_cmd(struct intel_sdvo *intel_sdvo, u8 cmd,
+				 const void *args, int args_len)
+{
+	return __intel_sdvo_write_cmd(intel_sdvo, cmd, args, args_len, true);
+}
+
 static bool intel_sdvo_read_response(struct intel_sdvo *intel_sdvo,
 				     void *response, int response_len)
 {
@@ -602,13 +612,13 @@ static int intel_sdvo_get_pixel_multiplier(const struct drm_display_mode *adjust
 		return 4;
 }
 
-static bool intel_sdvo_set_control_bus_switch(struct intel_sdvo *intel_sdvo,
+static bool __intel_sdvo_set_control_bus_switch(struct intel_sdvo *intel_sdvo,
 						u8 ddc_bus)
 {
 	/* This must be the immediately preceding write before the i2c xfer */
-	return intel_sdvo_write_cmd(intel_sdvo,
+	return __intel_sdvo_write_cmd(intel_sdvo,
 				      SDVO_CMD_SET_CONTROL_BUS_SWITCH,
-				    &ddc_bus, 1);
+				      &ddc_bus, 1, false);
 }
 
 static bool intel_sdvo_set_value(struct intel_sdvo *intel_sdvo, u8 cmd, const void *data, int len)
@@ -2926,7 +2936,7 @@ static int intel_sdvo_ddc_proxy_xfer(struct i2c_adapter *adapter,
 {
 	struct intel_sdvo *sdvo = adapter->algo_data;
 
-	if (!intel_sdvo_set_control_bus_switch(sdvo, sdvo->ddc_bus))
+	if (!__intel_sdvo_set_control_bus_switch(sdvo, sdvo->ddc_bus))
 		return -EIO;
 
 	return sdvo->i2c->algo->master_xfer(sdvo->i2c, msgs, num);
@@ -2943,6 +2953,33 @@ static const struct i2c_algorithm intel_sdvo_ddc_proxy = {
 	.functionality	= intel_sdvo_ddc_proxy_func
 };
 
+static void proxy_lock_bus(struct i2c_adapter *adapter,
+			   unsigned int flags)
+{
+	struct intel_sdvo *sdvo = adapter->algo_data;
+	sdvo->i2c->lock_ops->lock_bus(sdvo->i2c, flags);
+}
+
+static int proxy_trylock_bus(struct i2c_adapter *adapter,
+			     unsigned int flags)
+{
+	struct intel_sdvo *sdvo = adapter->algo_data;
+	return sdvo->i2c->lock_ops->trylock_bus(sdvo->i2c, flags);
+}
+
+static void proxy_unlock_bus(struct i2c_adapter *adapter,
+			     unsigned int flags)
+{
+	struct intel_sdvo *sdvo = adapter->algo_data;
+	sdvo->i2c->lock_ops->unlock_bus(sdvo->i2c, flags);
+}
+
+const struct i2c_lock_operations proxy_lock_ops = {
+	.lock_bus =    proxy_lock_bus,
+	.trylock_bus = proxy_trylock_bus,
+	.unlock_bus =  proxy_unlock_bus,
+};
+
 static bool
 intel_sdvo_init_ddc_proxy(struct intel_sdvo *sdvo,
 			  struct drm_i915_private *dev_priv)
@@ -2955,6 +2992,7 @@ intel_sdvo_init_ddc_proxy(struct intel_sdvo *sdvo,
 	sdvo->ddc.dev.parent = &pdev->dev;
 	sdvo->ddc.algo_data = sdvo;
 	sdvo->ddc.algo = &intel_sdvo_ddc_proxy;
+	sdvo->ddc.lock_ops = &proxy_lock_ops;
 
 	return i2c_add_adapter(&sdvo->ddc) == 0;
 }