On Fri, 07 Nov 2014, ville.syrjala@xxxxxxxxxxxxxxx wrote:
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxx>
> Suggested-by: Jani Nikula <jani.nikula@xxxxxxxxx>
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Reviewed-by: Jani Nikula <jani.nikula@xxxxxxxxx>
> ---
> 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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