drm/i915/intel_i2c: refactor using intel_gmbus_get_adapter

Instead of letting other modules directly access the ->gmbus array,
introduce intel_gmbus_get_adapter() for looking up an i2c_adapter
for a given gmbus port identifier.  This will enable later refactoring
of the gmbus port list.

Note: Before requesting an adapter for a given gmbus port number, the
driver must first check its validity using i2c_intel_gmbus_is_port_valid().
If this check fails, a call to intel_gmbus_get_adapter() will WARN_ON and
return NULL.  This is relevant for parts of the driver that read a port
from VBIOS, which might be improperly initialized and contain an invalid
port.  In these cases, the driver must fall back to using a safer default
port.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_dvo.c b/drivers/gpu/drm/i915/intel_dvo.c
index 020a7d7..60ba50b9 100644
--- a/drivers/gpu/drm/i915/intel_dvo.c
+++ b/drivers/gpu/drm/i915/intel_dvo.c
@@ -243,7 +243,7 @@
 	 * that's not the case.
 	 */
 	intel_ddc_get_modes(connector,
-			    &dev_priv->gmbus[GMBUS_PORT_DPC].adapter);
+			    intel_gmbus_get_adapter(dev_priv, GMBUS_PORT_DPC));
 	if (!list_empty(&connector->probed_modes))
 		return 1;
 
@@ -375,7 +375,7 @@
 		 * special cases, but otherwise default to what's defined
 		 * in the spec.
 		 */
-		if (dvo->gpio != 0)
+		if (intel_gmbus_is_port_valid(dvo->gpio))
 			gpio = dvo->gpio;
 		else if (dvo->type == INTEL_DVO_CHIP_LVDS)
 			gpio = GMBUS_PORT_SSC;
@@ -386,7 +386,7 @@
 		 * It appears that everything is on GPIOE except for panels
 		 * on i830 laptops, which are on GPIOB (DVOA).
 		 */
-		i2c = &dev_priv->gmbus[gpio].adapter;
+		i2c = intel_gmbus_get_adapter(dev_priv, gpio);
 
 		intel_dvo->dev = *dvo;
 		if (!dvo->dev_ops->init(&intel_dvo->dev, i2c))