Re: [PATCH v2 2/6] drm/i915: Skip .get_backlight() when backlight isn't enabled

[Jani Nikula <jani.nikula@intel.com>]

On Fri, 07 Nov 2014, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> On VLV/CHV when the display is off, we can't read out the current
> backlight level from the hardware since we have no pipe to do so.
> Currently we end up reading a bigus register due to passing
> INVALID_PIPE to VLV_BLC_PWM_CTL().
>
> Skip the entire .get_backlight() call if the backlight isn't enabled
> according to backlight.enabled.
>
> This problem can be reproduced simply by reading the backlight device
> actual_brightness file while the display is off.
>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Suggested-by: Jani Nikula <jani.nikula@intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

> ---
>  drivers/gpu/drm/i915/intel_panel.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
> index ef646b1..4ec6c2f 100644
> --- a/drivers/gpu/drm/i915/intel_panel.c
> +++ b/drivers/gpu/drm/i915/intel_panel.c
> @@ -539,12 +539,15 @@ static u32 intel_panel_get_backlight(struct intel_connector *connector)
>  {
>  	struct drm_device *dev = connector->base.dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> -	u32 val;
> +	struct intel_panel *panel = &connector->panel;
> +	u32 val = 0;
>  
>  	mutex_lock(&dev_priv->backlight_lock);
>  
> -	val = dev_priv->display.get_backlight(connector);
> -	val = intel_panel_compute_brightness(connector, val);
> +	if (panel->backlight.enabled) {
> +		val = dev_priv->display.get_backlight(connector);
> +		val = intel_panel_compute_brightness(connector, val);
> +	}
>  
>  	mutex_unlock(&dev_priv->backlight_lock);
>  
> -- 
> 2.0.4
>
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-- 
Jani Nikula, Intel Open Source Technology Center
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