drm/i915: abstract i2c bit banging fallback in gmbus xfer

Choose between i2c bit banging and gmbus in a new higher level function,
and let the i2c core retry the first time we fall back to bit banging.

The i2c core imposes a timeout on -EAGAIN, but it defaults to 1 second,
and shouldn't be a problem for us.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1448980166-23055-2-git-send-email-jani.nikula@intel.com

1 files changed, 25 insertions, 14 deletions

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index ccb522c176bd..e26e22a72e3b 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -472,9 +472,7 @@ gmbus_xfer_index_read(struct drm_i915_private *dev_priv, struct i2c_msg *msgs)
 }
 
 static int
-gmbus_xfer(struct i2c_adapter *adapter,
-           struct i2c_msg *msgs,
-           int num)
+do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
 {
         struct intel_gmbus *bus = container_of(adapter,
                                                struct intel_gmbus,
@@ -483,14 +481,6 @@ gmbus_xfer(struct i2c_adapter *adapter,
         int i = 0, inc, try = 0;
         int ret = 0;
 
-        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);
-                goto out;
-        }
-
 retry:
         I915_WRITE(GMBUS0, bus->reg0);
 
@@ -585,13 +575,34 @@ timeout:
                  bus->adapter.name, bus->reg0 & 0xff);
         I915_WRITE(GMBUS0, 0);
 
-        /* Hardware may not support GMBUS over these pins? Try GPIO bitbanging instead. */
+        /*
+         * Hardware may not support GMBUS over these pins? Try GPIO bitbanging
+         * instead. Use EAGAIN to have i2c core retry.
+         */
         bus->force_bit = 1;
-        ret = i2c_bit_algo.master_xfer(adapter, msgs, num);
+        ret = -EAGAIN;
 
 out:
-        mutex_unlock(&dev_priv->gmbus_mutex);
+        return ret;
+}
+
+static int
+gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
+{
+        struct intel_gmbus *bus = container_of(adapter, struct intel_gmbus,
+                                               adapter);
+        struct drm_i915_private *dev_priv = bus->dev_priv;
+        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);
+        else
+                ret = do_gmbus_xfer(adapter, msgs, num);
 
+        mutex_unlock(&dev_priv->gmbus_mutex);
         intel_display_power_put(dev_priv, POWER_DOMAIN_GMBUS);
 
         return ret;