---

yaml
---
r: 243678
b: refs/heads/master
c: 7f58aab
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 9f01b25048ad12b5d71f4f7d3b62ef737639a08d
+refs/heads/master: 7f58aabc369014fda3a4a33604ba0a1b63b941ac

trunk/drivers/gpu/drm/i915/intel_i2c.c

@@ -259,7 +259,7 @@ gmbus_xfer(struct i2c_adapter *adapter,
 				if (wait_for(I915_READ(GMBUS2 + reg_offset) & (GMBUS_SATOER | GMBUS_HW_RDY), 50))
 					goto timeout;
 				if (I915_READ(GMBUS2 + reg_offset) & GMBUS_SATOER)
-					return 0;
+					goto clear_err;
 
 				val = I915_READ(GMBUS3 + reg_offset);
 				do {
@@ -287,7 +287,7 @@ gmbus_xfer(struct i2c_adapter *adapter,
 				if (wait_for(I915_READ(GMBUS2 + reg_offset) & (GMBUS_SATOER | GMBUS_HW_RDY), 50))
 					goto timeout;
 				if (I915_READ(GMBUS2 + reg_offset) & GMBUS_SATOER)
-					return 0;
+					goto clear_err;
 
 				val = loop = 0;
 				do {
@@ -302,14 +302,31 @@ gmbus_xfer(struct i2c_adapter *adapter,
 		if (i + 1 < num && wait_for(I915_READ(GMBUS2 + reg_offset) & (GMBUS_SATOER | GMBUS_HW_WAIT_PHASE), 50))
 			goto timeout;
 		if (I915_READ(GMBUS2 + reg_offset) & GMBUS_SATOER)
-			return 0;
+			goto clear_err;
 	}
 
-	return num;
+	goto done;
+
+clear_err:
+	/* 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);
+
+done:
+	/* Mark the GMBUS interface as disabled. We will re-enable it at the
+	 * start of the next xfer, till then let it sleep.
+	 */
+	I915_WRITE(GMBUS0 + reg_offset, 0);
+	return i;
 
 timeout:
 	DRM_INFO("GMBUS timed out, falling back to bit banging on pin %d [%s]\n",
 		 bus->reg0 & 0xff, bus->adapter.name);
+	I915_WRITE(GMBUS0 + reg_offset, 0);
+
 	/* 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)