drm/i915: save/restore BLC histogram control reg across suspend/resume

Turns out some machines, like the ThinkPad X40 don't come back if you
don't save/restore this register.
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NEric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_drv.h

@@ -304,6 +304,7 @@ typedef struct drm_i915_private {
 	u32 saveDSPASURF;
 	u32 saveDSPATILEOFF;
 	u32 savePFIT_PGM_RATIOS;
+	u32 saveBLC_HIST_CTL;
 	u32 saveBLC_PWM_CTL;
 	u32 saveBLC_PWM_CTL2;
 	u32 saveFPB0;

drivers/gpu/drm/i915/i915_reg.h

@@ -1080,6 +1080,8 @@
 #define   BACKLIGHT_DUTY_CYCLE_SHIFT		(0)
 #define   BACKLIGHT_DUTY_CYCLE_MASK		(0xffff)
 
+#define BLC_HIST_CTL		0x61260
+
 /* TV port control */
 #define TV_CTL			0x68000
 /** Enables the TV encoder */

drivers/gpu/drm/i915/i915_suspend.c

@@ -410,6 +410,7 @@ void i915_save_display(struct drm_device *dev)
 	dev_priv->savePP_CONTROL = I915_READ(PP_CONTROL);
 	dev_priv->savePFIT_PGM_RATIOS = I915_READ(PFIT_PGM_RATIOS);
 	dev_priv->saveBLC_PWM_CTL = I915_READ(BLC_PWM_CTL);
+	dev_priv->saveBLC_HIST_CTL = I915_READ(BLC_HIST_CTL);
 	if (IS_I965G(dev))
 		dev_priv->saveBLC_PWM_CTL2 = I915_READ(BLC_PWM_CTL2);
 	if (IS_MOBILE(dev) && !IS_I830(dev))
@@ -501,6 +502,7 @@ void i915_restore_display(struct drm_device *dev)
 
 	I915_WRITE(PFIT_PGM_RATIOS, dev_priv->savePFIT_PGM_RATIOS);
 	I915_WRITE(BLC_PWM_CTL, dev_priv->saveBLC_PWM_CTL);
+	I915_WRITE(BLC_HIST_CTL, dev_priv->saveBLC_HIST_CTL);
 	I915_WRITE(PP_ON_DELAYS, dev_priv->savePP_ON_DELAYS);
 	I915_WRITE(PP_OFF_DELAYS, dev_priv->savePP_OFF_DELAYS);
 	I915_WRITE(PP_DIVISOR, dev_priv->savePP_DIVISOR);