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

1 files changed, 34 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 3c9e00d4ba5a..6698826954e1 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/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