Patch "drm/i915/backlight: setup backlight pwm alternate increment on backlight enable" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

drm/i915/backlight: setup backlight pwm alternate increment on backlight enable

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-i915-backlight-setup-backlight-pwm-alternate-increment-on-backlight-enable.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Shawn Lee <[email protected]>
Date: Mon, 19 Sep 2016 13:35:26 +0300
Subject: drm/i915/backlight: setup backlight pwm alternate increment on backlight enable
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From: Shawn Lee <[email protected]>

commit 915b417946030e1f365c63728875cffd8db8e880 upstream.

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
References: https://bugs.freedesktop.org/show_bug.cgi?id=67454

---
 drivers/gpu/drm/i915/intel_panel.c |   18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

@@ -841,7 +841,7 @@ static void lpt_enable_backlight(struct
 {
 	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
 		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);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/drm-i915-backlight-setup-backlight-pwm-alternate-increment-on-backlight-enable.patch queue-4.8/drm-i915-backlight-setup-and-cache-pwm-alternate-increment-value.patch