drm/i915: retry gmbus transfers after first NAKhpd-mess

Paulo Zanoni has a machine with too many bogons.

Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 1991a4408cf9..ca0169d759a9 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -333,6 +333,7 @@ gmbus_xfer(struct i2c_adapter *adapter,
 	struct drm_i915_private *dev_priv = bus->dev_priv;
 	int i, reg_offset;
 	int ret = 0;
+	bool repeat = false;
 
 	mutex_lock(&dev_priv->gmbus_mutex);
 
@@ -343,6 +344,7 @@ gmbus_xfer(struct i2c_adapter *adapter,
 
 	reg_offset = dev_priv->gpio_mmio_base;
 
+repeat:
 	I915_WRITE(GMBUS0 + reg_offset, bus->reg0);
 
 	for (i = 0; i < num; i++) {
@@ -421,6 +423,17 @@ clear_err:
 	I915_WRITE(GMBUS1 + reg_offset, 0);
 	I915_WRITE(GMBUS0 + reg_offset, 0);
 
+	/*
+	 * GMBUS is a fickle thing, and especially on wire pairs shared with
+	 * other stuff (e.g. dp aux transfers) we need to clear bogons first
+	 * before we can be sure that the NAK is real. So just retry once after
+	 * resetting the bus.
+	 */
+	if (!repeat) {
+		repeat = true;
+		goto repeat;
+	}
+
 	DRM_DEBUG_KMS("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);