[PATCH 5/5] drm/i915/gmbus: Reset the controller on initialisation

[Chris Wilson <chris@chris-wilson.co.uk>]

Toggle the Software Clear Interrupt bit which resets the controller to
clear any prior BUS_ERROR condition before we begin to use the
controller in earnest.

Suggested-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_i2c.c |   14 +++++++++++---
 1 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index d3b903b..f9f0c42 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -55,10 +55,18 @@ void
 intel_i2c_reset(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
+	int reg_offset;
+
+	reg_offset = 0;
 	if (HAS_PCH_SPLIT(dev))
-		I915_WRITE(PCH_GMBUS0, 0);
-	else
-		I915_WRITE(GMBUS0, 0);
+		reg_offset = PCH_GMBUS0 - GMBUS0;
+
+	/* First reset the controller by toggling the Sw Clear Interrupt. */
+	I915_WRITE(GMBUS1 + reg_offset, GMBUS_SW_CLR_INT);
+	I915_WRITE(GMBUS1 + reg_offset, 0);
+
+	/* Then mark the controller as disabled. */
+	I915_WRITE(GMBUS0 + reg_offset, 0);
 }
 
 static void intel_i2c_quirk_set(struct drm_i915_private *dev_priv, bool enable)
-- 
1.7.4.1