[Intel-gfx] drivers: i915: Default max backlight brightness value

[Simon Que]

Use 0x1000 as the default backlight PWM max value and period.  This is
passed in as a module parameter to i915_drv and is used to program the
PWM registers.  It can be set to other values based on the needs of each
system.

Signed-off-by: Simon Que <sque at chromium.org>
---
 drivers/gpu/drm/i915/i915_reg.h    |    1 +
 drivers/gpu/drm/i915/intel_panel.c |   29 +++++++++++++++++------------
 2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 5d5def7..a832028 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -3275,6 +3275,7 @@
 #define  PWM_POLARITY_ACTIVE_HIGH2	(0 << 28)
 
 #define BLC_PWM_PCH_CTL2	0xc8254
+#define BLC_PWM_PCH_FREQ_SHIFT	16
 
 #define PCH_PP_STATUS		0xc7200
 #define PCH_PP_CONTROL		0xc7204
diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 05f500c..b5d2244 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -133,27 +133,32 @@ static u32 i915_read_blc_pwm_ctl(struct drm_i915_private *dev_priv)
 {
 	u32 val;
 
-	/* Restore the CTL value if it lost, e.g. GPU reset */
-
+	/* Restore the CTL value if it was lost, e.g. GPU reset */
+	/* Use the default PWM max if none is available. */
 	if (HAS_PCH_SPLIT(dev_priv->dev)) {
 		val = I915_READ(BLC_PWM_PCH_CTL2);
-		if (dev_priv->saveBLC_PWM_CTL2 == 0) {
+		if (dev_priv->saveBLC_PWM_CTL2 == 0 && val == 0)
+			dev_priv->saveBLC_PWM_CTL2 =
+				i915_max_backlight << BLC_PWM_PCH_FREQ_SHIFT;
+		else if (dev_priv->saveBLC_PWM_CTL2 == 0)
 			dev_priv->saveBLC_PWM_CTL2 = val;
-		} else if (val == 0) {
+		if (val == 0) {
 			I915_WRITE(BLC_PWM_PCH_CTL2,
-				   dev_priv->saveBLC_PWM_CTL);
-			val = dev_priv->saveBLC_PWM_CTL;
+				   dev_priv->saveBLC_PWM_CTL2);
+			val = dev_priv->saveBLC_PWM_CTL2;
 		}
 	} else {
 		val = I915_READ(BLC_PWM_CTL);
-		if (dev_priv->saveBLC_PWM_CTL == 0) {
+		if (dev_priv->saveBLC_PWM_CTL == 0 && val == 0) {
+			dev_priv->saveBLC_PWM_CTL = i915_max_backlight
+				<< BACKLIGHT_MODULATION_FREQ_SHIFT;
+		} else if (dev_priv->saveBLC_PWM_CTL == 0) {
 			dev_priv->saveBLC_PWM_CTL = val;
 			dev_priv->saveBLC_PWM_CTL2 = I915_READ(BLC_PWM_CTL2);
-		} else if (val == 0) {
-			I915_WRITE(BLC_PWM_CTL,
-				   dev_priv->saveBLC_PWM_CTL);
-			I915_WRITE(BLC_PWM_CTL2,
-				   dev_priv->saveBLC_PWM_CTL2);
+		}
+		if (val == 0) {
+			I915_WRITE(BLC_PWM_CTL, dev_priv->saveBLC_PWM_CTL);
+			I915_WRITE(BLC_PWM_CTL2, dev_priv->saveBLC_PWM_CTL2);
 			val = dev_priv->saveBLC_PWM_CTL;
 		}
 	}
-- 
1.7.2.3