drm/i915: Fall back to bit banging mode for DVO transmitter detection

commit e4bfff54ed3f5de88f5358504c78c2cb037813aa upstream.

As discussed in this thread
http://lists.freedesktop.org/archives/dri-devel/2013-April/037411.html
GMBUS based DVO transmitter detection seems to be unreliable which could
result in an unusable DVO port.

The attached patch fixes this by falling back to bit banging mode for
the time DVO transmitter detection is in progress.

Signed-off-by: David Müller <d.mueller@elsoft.ch>
Tested-by: David Müller <d.mueller@elsoft.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/i915/intel_dvo.c b/drivers/gpu/drm/i915/intel_dvo.c
index 020a7d7f744dcc9608d9a652d2b0d0d4b1035ea7..69bea56e5162a08cc2cc002d354e0be9fe891a49 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dvo.c
+++ b/drivers/gpu/drm/i915/intel_dvo.c
@@ -370,6 +370,7 @@ void intel_dvo_init(struct drm_device *dev)
                const struct intel_dvo_device *dvo = &intel_dvo_devices[i];
                struct i2c_adapter *i2c;
                int gpio;
+               bool dvoinit;
 
                /* Allow the I2C driver info to specify the GPIO to be used in
                 * special cases, but otherwise default to what's defined
@@ -389,7 +390,17 @@ void intel_dvo_init(struct drm_device *dev)
                i2c = &dev_priv->gmbus[gpio].adapter;
 
                intel_dvo->dev = *dvo;
-               if (!dvo->dev_ops->init(&intel_dvo->dev, i2c))
+
+               /* GMBUS NAK handling seems to be unstable, hence let the
+                * transmitter detection run in bit banging mode for now.
+                */
+               intel_gmbus_force_bit(i2c, true);
+
+               dvoinit = dvo->dev_ops->init(&intel_dvo->dev, i2c);
+
+               intel_gmbus_force_bit(i2c, false);
+
+               if (!dvoinit)
                        continue;
 
                intel_encoder->type = INTEL_OUTPUT_DVO;