i915/kms/backlight-combo mode problem (was: Re: Linux 2.6.39-rc5)

[Takashi Iwai]

At Sat, 30 Apr 2011 10:32:04 +0200,
Melchior FRANZ wrote:
> 
> * Takashi Iwai -- Saturday 30 April 2011:
> > I remember vaguely that the value zero could be interpreted as the max.
> 
> > Also, with the patch, does the backlight level can be adjusted
> > correctly to different values?  I wonder whether LBPC adjustment
> > really works or not on your machine.
> 
> > +			if (!lbpc)
> > +				lbpc = 0xff; /* max value */
> 
> This change does *not* work on my machine. The screen stays black
> again.

Hrm, then it's really hard to say how exactly the system behaves when
lbpc=0...  I guess we should avoid controlling LBPC in such a case,
e.g. something like the patch below (totally untested).

But Intel guys must know of this better... I leave this to their
hands.

> 
> Yes, backlight adjustment generally works on this notebook, but only
> with "acpi_osi=Linux" on the command line.

acpi_osi quirk should be better added statically, then.


thanks,

Takashi

---
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 1c1b27c..c0ab771 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -328,6 +328,7 @@ typedef struct drm_i915_private {
 	struct intel_overlay *overlay;
 
 	/* LVDS info */
+	int backlight_combination_mode; /* 0=unknown, -1=no, 1=yes */
 	int backlight_level;  /* restore backlight to this value */
 	bool backlight_enabled;
 	struct drm_display_mode *panel_fixed_mode;
diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
index a06ff07..320dd5f 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -115,14 +115,24 @@ done:
 static int is_backlight_combination_mode(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-
-	if (INTEL_INFO(dev)->gen >= 4)
-		return I915_READ(BLC_PWM_CTL2) & BLM_COMBINATION_MODE;
-
-	if (IS_GEN2(dev))
-		return I915_READ(BLC_PWM_CTL) & BLM_LEGACY_MODE;
-
-	return 0;
+	int combo_mode;
+	u8 lbpc;
+
+	if (dev_priv->backlight_combination_mode)
+		return dev_priv->backlight_combination_mode > 0;
+
+	pci_read_config_byte(dev->pdev, PCI_LBPC, &lbpc);
+	if (!lbpc)
+		combo_mode = 0;
+	else if (INTEL_INFO(dev)->gen >= 4)
+		combo_mode = I915_READ(BLC_PWM_CTL2) & BLM_COMBINATION_MODE;
+	else if (IS_GEN2(dev))
+		combo_mode = I915_READ(BLC_PWM_CTL) & BLM_LEGACY_MODE;
+	else
+		combo_mode = 0;
+
+	dev_priv->backlight_combination_mode = combo_mode ? -1 : 1;
+	return combo_mode;
 }
 
 static u32 i915_read_blc_pwm_ctl(struct drm_i915_private *dev_priv)