[Intel-gfx] [PATCH] drm/i915: don't forget the PCH backlight registers

[Paulo Zanoni]

From: Paulo Zanoni <paulo.r.zanoni at intel.com>

When we enable/disable the CPU backlight registers we can't forget to
enable/disable the PCH backlight registers. Since we're using the CPU
registers we should also unset the override bit.

Fixes a regression on the following commit:
  drm/i915: properly enable the blc controller on the right pipe

The commit just deleted the code that sets the PCH registers, so it
was relying on the values set by the BIOS. I told my BIOS to boot on
the DVI monitor instead of the LVDS panel, so I noticed the bug.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
---
 drivers/gpu/drm/i915/intel_panel.c |   15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)


I really think this patch fixes fd.o bug #51463. I'm waiting
confirmation from the bug reporter.

Also, I did not really do the git bisect: I understood it is a
regression from that commit just by reading the commit (and by
the fact that backlight used to work until I upgraded my
Kernel).

diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index 58c7ee7..10c7d39 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -289,11 +289,17 @@ void intel_panel_disable_backlight(struct drm_device *dev)
 	intel_panel_actually_set_backlight(dev, 0);
 
 	if (INTEL_INFO(dev)->gen >= 4) {
-		uint32_t reg;
+		uint32_t reg, tmp;
 
 		reg = HAS_PCH_SPLIT(dev) ? BLC_PWM_CPU_CTL2 : BLC_PWM_CTL2;
 
 		I915_WRITE(reg, I915_READ(reg) & ~BLM_PWM_ENABLE);
+
+		if (HAS_PCH_SPLIT(dev)) {
+			tmp = I915_READ(BLC_PWM_PCH_CTL1);
+			tmp &= ~BLM_PCH_PWM_ENABLE;
+			I915_WRITE(BLC_PWM_PCH_CTL1, tmp);
+		}
 	}
 }
 
@@ -333,6 +339,13 @@ void intel_panel_enable_backlight(struct drm_device *dev,
 		I915_WRITE(reg, tmp);
 		POSTING_READ(reg);
 		I915_WRITE(reg, tmp | BLM_PWM_ENABLE);
+
+		if (HAS_PCH_SPLIT(dev)) {
+			tmp = I915_READ(BLC_PWM_PCH_CTL1);
+			tmp |= BLM_PCH_PWM_ENABLE;
+			tmp &= ~BLM_PCH_OVERRIDE_ENABLE;
+			I915_WRITE(BLC_PWM_PCH_CTL1, tmp);
+		}
 	}
 }
 
-- 
1.7.10.4