drm/i915: save/restore GMBUS freq across suspend/resume on gen4

commit 9f49c376 upstream.

Should probably just init this in the GMbus code all the time, based on
the cdclk and HPLL like we do on newer platforms.  Ville has code for
that in a rework branch, but until then we can fix this bug fairly
easily.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=76301Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Tested-by: Nikolay <mar.kolya@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/gpu/drm/i915/i915_drv.h

@@ -876,6 +876,7 @@ struct i915_suspend_saved_registers {
 	u32 savePIPEB_LINK_N1;
 	u32 saveMCHBAR_RENDER_STANDBY;
 	u32 savePCH_PORT_HOTPLUG;
+	u16 saveGCDGMBUS;
 };
 
 struct intel_gen6_power_mgmt {

drivers/gpu/drm/i915/i915_reg.h

@@ -74,6 +74,7 @@
 #define   I915_GC_RENDER_CLOCK_200_MHZ	(1 << 0)
 #define   I915_GC_RENDER_CLOCK_333_MHZ	(4 << 0)
 #define LBB	0xf4
+#define GCDGMBUS 0xcc
 
 /* Graphics reset regs */
 #define I965_GDRST 0xc0 /* PCI config register */

drivers/gpu/drm/i915/i915_suspend.c

@@ -397,6 +397,10 @@ int i915_save_state(struct drm_device *dev)
 
 	intel_disable_gt_powersave(dev);
 
+	if (IS_GEN4(dev))
+		pci_read_config_word(dev->pdev, GCDGMBUS,
+				     &dev_priv->regfile.saveGCDGMBUS);
+
 	/* Cache mode state */
 	if (INTEL_INFO(dev)->gen < 7)
 		dev_priv->regfile.saveCACHE_MODE_0 = I915_READ(CACHE_MODE_0);
@@ -429,6 +433,10 @@ int i915_restore_state(struct drm_device *dev)
 	mutex_lock(&dev->struct_mutex);
 
 	i915_gem_restore_fences(dev);
+
+	if (IS_GEN4(dev))
+		pci_write_config_word(dev->pdev, GCDGMBUS,
+				      dev_priv->regfile.saveGCDGMBUS);
 	i915_restore_display(dev);
 
 	if (!drm_core_check_feature(dev, DRIVER_MODESET)) {