[Intel-gfx] [PATCH] drm/i915: Use the correct GMCH_CTRL register for Sandybridge+

[Chris Wilson]

The GMCH_CTRL register (or MGCC in the spec) is at a different address
on Sandybridge, and the address to which we currently write to is
undefined. These stray writes appear to upset (hard hang) my Ivybridge
machine whilst it is in UEFI mode.

Note that the register is still marked as locked RO on Sandybridge, so
vgaarb is still dysfunctional.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: stable at vger.kernel.org
---
 drivers/gpu/drm/i915/intel_display.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 7db292c469af..9caf6a879f31 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -11334,9 +11334,10 @@ void intel_connector_attach_encoder(struct intel_connector *connector,
 int intel_modeset_vga_set_state(struct drm_device *dev, bool state)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
+	unsigned reg = INTEL_INFO(dev)->gen >= 6 ? SNB_GMCH_CTRL : INTEL_GMCH_CTRL;
 	u16 gmch_ctrl;
 
-	if (pci_read_config_word(dev_priv->bridge_dev, INTEL_GMCH_CTRL, &gmch_ctrl)) {
+	if (pci_read_config_word(dev_priv->bridge_dev, reg, &gmch_ctrl)) {
 		DRM_ERROR("failed to read control word\n");
 		return -EIO;
 	}
@@ -11346,7 +11347,7 @@ int intel_modeset_vga_set_state(struct drm_device *dev, bool state)
 	else
 		gmch_ctrl |= INTEL_GMCH_VGA_DISABLE;
 
-	if (pci_write_config_word(dev_priv->bridge_dev, INTEL_GMCH_CTRL, gmch_ctrl)) {
+	if (pci_write_config_word(dev_priv->bridge_dev, reg, gmch_ctrl)) {
 		DRM_ERROR("failed to write control word\n");
 		return -EIO;
 	}
-- 
1.8.5.1