drm/i915/intel_i2c: always wait for IDLE before clearing NAK

[karo-tx-linux.git] / drivers / gpu / drm / i915 / intel_i2c.c

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index f02e52aca7467d571f893beb55ffa8cfbe8abab4..9707868881ec16ea92afa5bf272a51b8600d174d 100644 (file)
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -324,26 +324,47 @@ gmbus_xfer(struct i2c_adapter *adapter,
                        goto clear_err;
        }
 
-       goto done;
+       /* Mark the GMBUS interface as disabled after waiting for idle.
+        * We will re-enable it at the start of the next xfer,
+        * till then let it sleep.
+        */
+       if (wait_for((I915_READ(GMBUS2 + reg_offset) & GMBUS_ACTIVE) == 0, 10))
+               DRM_INFO("GMBUS [%s] timed out waiting for idle\n",
+                        adapter->name);
+       I915_WRITE(GMBUS0 + reg_offset, 0);
+       ret = i;
+       goto out;
 
 clear_err:
+       /*
+        * Wait for bus to IDLE before clearing NAK.
+        * If we clear the NAK while bus is still active, then it will stay
+        * active and the next transaction may fail.
+        */
+       if (wait_for((I915_READ(GMBUS2 + reg_offset) & GMBUS_ACTIVE) == 0,
+                    10))
+               DRM_INFO("GMBUS [%s] timed out after NAK\n", adapter->name);
+
        /* Toggle the Software Clear Interrupt bit. This has the effect
         * of resetting the GMBUS controller and so clearing the
         * BUS_ERROR raised by the slave's NAK.
         */
        I915_WRITE(GMBUS1 + reg_offset, GMBUS_SW_CLR_INT);
        I915_WRITE(GMBUS1 + reg_offset, 0);
+       I915_WRITE(GMBUS0 + reg_offset, 0);
 
-done:
-       /* Mark the GMBUS interface as disabled after waiting for idle.
-        * We will re-enable it at the start of the next xfer,
-        * till then let it sleep.
+       DRM_DEBUG_DRIVER("GMBUS [%s] NAK for addr: %04x %c(%d)\n",
+                        adapter->name, msgs[i].addr,
+                        (msgs[i].flags & I2C_M_RD) ? 'r' : 'w', msgs[i].len);
+
+       /*
+        * If no ACK is received during the address phase of a transaction,
+        * the adapter must report -ENXIO.
+        * It is not clear what to return if no ACK is received at other times.
+        * So, we always return -ENXIO in all NAK cases, to ensure we send
+        * it at least during the one case that is specified.
         */
-       if (wait_for((I915_READ(GMBUS2 + reg_offset) & GMBUS_ACTIVE) == 0, 10))
-               DRM_INFO("GMBUS [%s] timed out waiting for idle\n",
-                        bus->adapter.name);
-       I915_WRITE(GMBUS0 + reg_offset, 0);
-       ret = i;
+       ret = -ENXIO;
        goto out;
 
 timeout: