Bit #28 of the backlight control BLC_PWM_CTL2 is normally used
to indicate whether the brightness of the panel backlight is
inverted. Sometimes, however, bit #29 is used for this purpose.
Add a quirk to mark machines that do so.

Signed-off-by: Carsten Emde <C.Emde@osadl.org>

---
 drivers/gpu/drm/i915/i915_drv.h      |    1 +
 drivers/gpu/drm/i915/i915_reg.h      |    1 +
 drivers/gpu/drm/i915/intel_display.c |   10 ++++++++++
 drivers/gpu/drm/i915/intel_panel.c   |   12 ++++++++++--
 4 files changed, 22 insertions(+), 2 deletions(-)

Index: linux-tip/drivers/gpu/drm/i915/i915_drv.h
===================================================================
--- linux-tip.orig/drivers/gpu/drm/i915/i915_drv.h
+++ linux-tip/drivers/gpu/drm/i915/i915_drv.h
@@ -295,6 +295,7 @@ enum intel_pch {
 
 #define QUIRK_PIPEA_FORCE (1<<0)
 #define QUIRK_LVDS_SSC_DISABLE (1<<1)
+#define QUIRK_ALT_BIT_FOR_BRIGHTNESS_INVERSION (2<<1)
 
 struct intel_fbdev;
 struct intel_fbc_work;
Index: linux-tip/drivers/gpu/drm/i915/i915_reg.h
===================================================================
--- linux-tip.orig/drivers/gpu/drm/i915/i915_reg.h
+++ linux-tip/drivers/gpu/drm/i915/i915_reg.h
@@ -1685,6 +1685,7 @@
 /* Backlight control */
 #define BLC_PWM_CTL2		0x61250 /* 965+ only */
 #define   BLM_COMBINATION_MODE	(1 << 30)
+#define   BLM_ALT_POLARITY_I965	(1 << 29) /* quirk only */
 #define   BLM_POLARITY_I965	(1 << 28) /* gen4 only */
 #define BLC_PWM_CTL		0x61254
 /*
Index: linux-tip/drivers/gpu/drm/i915/intel_display.c
===================================================================
--- linux-tip.orig/drivers/gpu/drm/i915/intel_display.c
+++ linux-tip/drivers/gpu/drm/i915/intel_display.c
@@ -9101,6 +9101,16 @@ static void quirk_ssc_force_disable(stru
 	dev_priv->quirks |= QUIRK_LVDS_SSC_DISABLE;
 }
 
+/*
+ * A machine may use an alternate bit to indicate panel backlight brightness
+ * inversion
+ */
+static void quirk_alt_bit_for_brightness_inversion(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	dev_priv->quirks |= QUIRK_ALT_BIT_FOR_BRIGHTNESS_INVERSION;
+}
+
 struct intel_quirk {
 	int device;
 	int subsystem_vendor;
Index: linux-tip/drivers/gpu/drm/i915/intel_panel.c
===================================================================
--- linux-tip.orig/drivers/gpu/drm/i915/intel_panel.c
+++ linux-tip/drivers/gpu/drm/i915/intel_panel.c
@@ -208,9 +208,17 @@ static u32 intel_panel_compute_brightnes
 	    dev_priv->quirks & QUIRK_INVERT_BRIGHTNESS)
 		return intel_panel_get_max_backlight(dev) - val;
 
-	/* gen4 has a polarity bit */
-	if (IS_GEN4(dev) && (I915_READ(BLC_PWM_CTL2) & BLM_POLARITY_I965))
+	if (IS_GEN4(dev)) {
+		/* gen4 has a - possibly quirked - polarity bit */
+		int mask;
+
+		if (dev_priv->quirks & QUIRK_ALT_BIT_FOR_BRIGHTNESS_INVERSION)
+			mask = BLM_ALT_POLARITY_I965;
+		else
+			mask = BLM_POLARITY_I965;
+		if (I915_READ(BLC_PWM_CTL2) & mask)
 			return intel_panel_get_max_backlight(dev) - val;
+	}
 
 	return val;
 }


