Re: [PATCH 3/4] drm/i915: add quirk to indicate that an alt bit is used for brightness inversion

From: Daniel Vetter <daniel@ffwll.ch>
To: Carsten Emde <C.Emde@osadl.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>
Subject: Re: [PATCH 3/4] drm/i915: add quirk to indicate that an alt bit is used for brightness inversion
Date: Thu, 26 Apr 2012 19:08:44 +0200	[thread overview]
Message-ID: <20120426170844.GG5156@phenom.ffwll.local> (raw)
In-Reply-To: <20120426165034.081110768@osadl.org>

On Thu, Apr 26, 2012 at 06:48:36PM +0200, Carsten Emde wrote:
> Bit #28 of the backlight control BLC_PWM_CTL2 is normally used
> to indicate whether the brightness of the panel backlight is
> inverted. Sometimes, however, bit #29 is used for this purpose.
> Add a quirk to mark machines that do so.
> 
> Signed-off-by: Carsten Emde <C.Emde@osadl.org>
> 
> ---
>  drivers/gpu/drm/i915/i915_drv.h      |    1 +
>  drivers/gpu/drm/i915/i915_reg.h      |    1 +
>  drivers/gpu/drm/i915/intel_display.c |   10 ++++++++++
>  drivers/gpu/drm/i915/intel_panel.c   |   12 ++++++++++--
>  4 files changed, 22 insertions(+), 2 deletions(-)
> 
> Index: linux-tip/drivers/gpu/drm/i915/i915_drv.h
> ===================================================================
> --- linux-tip.orig/drivers/gpu/drm/i915/i915_drv.h
> +++ linux-tip/drivers/gpu/drm/i915/i915_drv.h
> @@ -295,6 +295,7 @@ enum intel_pch {
>  
>  #define QUIRK_PIPEA_FORCE (1<<0)
>  #define QUIRK_LVDS_SSC_DISABLE (1<<1)
> +#define QUIRK_ALT_BIT_FOR_BRIGHTNESS_INVERSION (2<<1)
>  
>  struct intel_fbdev;
>  struct intel_fbc_work;
> Index: linux-tip/drivers/gpu/drm/i915/i915_reg.h
> ===================================================================
> --- linux-tip.orig/drivers/gpu/drm/i915/i915_reg.h
> +++ linux-tip/drivers/gpu/drm/i915/i915_reg.h
> @@ -1685,6 +1685,7 @@
>  /* Backlight control */
>  #define BLC_PWM_CTL2		0x61250 /* 965+ only */
>  #define   BLM_COMBINATION_MODE	(1 << 30)
> +#define   BLM_ALT_POLARITY_I965	(1 << 29) /* quirk only */

bit29 is the pipe select bit, i.e. the backlight controller uses the pixel
clock from this pipe as the signal to module the backlight.

I need to look some more into this.
-Daniel

>  #define   BLM_POLARITY_I965	(1 << 28) /* gen4 only */
>  #define BLC_PWM_CTL		0x61254
>  /*
> Index: linux-tip/drivers/gpu/drm/i915/intel_display.c
> ===================================================================
> --- linux-tip.orig/drivers/gpu/drm/i915/intel_display.c
> +++ linux-tip/drivers/gpu/drm/i915/intel_display.c
> @@ -9101,6 +9101,16 @@ static void quirk_ssc_force_disable(stru
>  	dev_priv->quirks |= QUIRK_LVDS_SSC_DISABLE;
>  }
>  
> +/*
> + * A machine may use an alternate bit to indicate panel backlight brightness
> + * inversion
> + */
> +static void quirk_alt_bit_for_brightness_inversion(struct drm_device *dev)
> +{
> +	struct drm_i915_private *dev_priv = dev->dev_private;
> +	dev_priv->quirks |= QUIRK_ALT_BIT_FOR_BRIGHTNESS_INVERSION;
> +}
> +
>  struct intel_quirk {
>  	int device;
>  	int subsystem_vendor;
> Index: linux-tip/drivers/gpu/drm/i915/intel_panel.c
> ===================================================================
> --- linux-tip.orig/drivers/gpu/drm/i915/intel_panel.c
> +++ linux-tip/drivers/gpu/drm/i915/intel_panel.c
> @@ -208,9 +208,17 @@ static u32 intel_panel_compute_brightnes
>  	    dev_priv->quirks & QUIRK_INVERT_BRIGHTNESS)
>  		return intel_panel_get_max_backlight(dev) - val;
>  
> -	/* gen4 has a polarity bit */
> -	if (IS_GEN4(dev) && (I915_READ(BLC_PWM_CTL2) & BLM_POLARITY_I965))
> +	if (IS_GEN4(dev)) {
> +		/* gen4 has a - possibly quirked - polarity bit */
> +		int mask;
> +
> +		if (dev_priv->quirks & QUIRK_ALT_BIT_FOR_BRIGHTNESS_INVERSION)
> +			mask = BLM_ALT_POLARITY_I965;
> +		else
> +			mask = BLM_POLARITY_I965;
> +		if (I915_READ(BLC_PWM_CTL2) & mask)
>  			return intel_panel_get_max_backlight(dev) - val;
> +	}
>  
>  	return val;
>  }
> 

-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48