[Intel-gfx] [PATCH] drm/i915/backlight: setup backlight pwm alternate increment on backlight enable

[Jani Nikula]

From: Shawn Lee <shawn.c.lee at intel.com>

Backlight enable is supposed to do a full setup of the backlight. We
were missing the PWM alternate increment bit in the south chicken
registers on lpt+ pch. This potentially caused a PWM frequency change
when the chicken register value was lost e.g. on suspend.

v2 by Jani, rebase on the patch caching alt increment

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97486
Cc: Cooper Chiou <cooper.chiou at intel.com>
Cc: Wei Shun Chen <wei.shun.chang at intel.com>
Cc: Gary C Wang <gary.c.wang at intel.com>
Cc: stable at vger.kernel.org
Signed-off-by: Shawn Lee <shawn.c.lee at intel.com>
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
---
 drivers/gpu/drm/i915/intel_panel.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 8bc43205d6a0..be4b4d546fd9 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -841,7 +841,7 @@ static void lpt_enable_backlight(struct intel_connector *connector)
 {
 	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
 	struct intel_panel *panel = &connector->panel;
-	u32 pch_ctl1, pch_ctl2;
+	u32 pch_ctl1, pch_ctl2, schicken;
 
 	pch_ctl1 = I915_READ(BLC_PWM_PCH_CTL1);
 	if (pch_ctl1 & BLM_PCH_PWM_ENABLE) {
@@ -850,6 +850,22 @@ static void lpt_enable_backlight(struct intel_connector *connector)
 		I915_WRITE(BLC_PWM_PCH_CTL1, pch_ctl1);
 	}
 
+	if (HAS_PCH_LPT(dev_priv)) {
+		schicken = I915_READ(SOUTH_CHICKEN2);
+		if (panel->backlight.alternate_pwm_increment)
+			schicken |= LPT_PWM_GRANULARITY;
+		else
+			schicken &= ~LPT_PWM_GRANULARITY;
+		I915_WRITE(SOUTH_CHICKEN2, schicken);
+	} else {
+		schicken = I915_READ(SOUTH_CHICKEN1);
+		if (panel->backlight.alternate_pwm_increment)
+			schicken |= SPT_PWM_GRANULARITY;
+		else
+			schicken &= ~SPT_PWM_GRANULARITY;
+		I915_WRITE(SOUTH_CHICKEN1, schicken);
+	}
+
 	pch_ctl2 = panel->backlight.max << 16;
 	I915_WRITE(BLC_PWM_PCH_CTL2, pch_ctl2);
 
-- 
2.1.4