Re: [PATCH 1/2] drm/i915: i915.enable_backlight=0 disables intel_backlight

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Apr 25, 2012 at 10:28:41AM -0700, Kamal Mostafa wrote:
> i915.enable_backlight=0 can be used to disable i915 backlight control
> and the /sys/class/backlight/intel_backlight interface -- useful for
> systems where intel_backight conflicts with BIOS backlight control.
> 
> BugLink: https://launchpad.net/bugs/954661
> Signed-off-by: Kamal Mostafa <kamal@canonical.com>

Ok, I've just gone through the fun of merging a set of backlight quirks a
few weeks back. Then noticed that an awful lot of machines seem to be
affected and later on read about a few interesting bits in the
documentation. Turns out the hw is all good, it's just the driver totally
mishandling the backlight.

To cut things short: This time around I want more justification for the
quirk than just "this makes this one machine work somehow".
-Daniel

> ---
>  drivers/gpu/drm/i915/i915_drv.c    |    6 ++++++
>  drivers/gpu/drm/i915/i915_drv.h    |    1 +
>  drivers/gpu/drm/i915/intel_panel.c |   12 ++++++++++++
>  3 files changed, 19 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index ae8a64f..ddb947b 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -112,6 +112,12 @@ module_param_named(i915_enable_ppgtt, i915_enable_ppgtt, int, 0600);
>  MODULE_PARM_DESC(i915_enable_ppgtt,
>  		"Enable PPGTT (default: true)");
>  
> +int i915_enable_backlight __read_mostly = -1;
> +module_param_named(enable_backlight, i915_enable_backlight, int, 0644);
> +MODULE_PARM_DESC(enable_backlight,
> +		"Enable backlight control and the intel_backlight interface. "
> +		"(default: -1 (auto))");
> +
>  static struct drm_driver driver;
>  extern int intel_agp_enabled;
>  
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 5fabc6c..6e52a42 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1087,6 +1087,7 @@ extern int i915_enable_rc6 __read_mostly;
>  extern int i915_enable_fbc __read_mostly;
>  extern bool i915_enable_hangcheck __read_mostly;
>  extern int i915_enable_ppgtt __read_mostly;
> +extern int i915_enable_backlight __read_mostly;
>  
>  extern int i915_suspend(struct drm_device *dev, pm_message_t state);
>  extern int i915_resume(struct drm_device *dev);
> diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
> index 48177ec..fcecbd2 100644
> --- a/drivers/gpu/drm/i915/intel_panel.c
> +++ b/drivers/gpu/drm/i915/intel_panel.c
> @@ -259,6 +259,9 @@ void intel_panel_disable_backlight(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  
> +	if (!i915_enable_backlight)
> +		return;
> +
>  	dev_priv->backlight_enabled = false;
>  	intel_panel_actually_set_backlight(dev, 0);
>  }
> @@ -267,6 +270,9 @@ void intel_panel_enable_backlight(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  
> +	if (!i915_enable_backlight)
> +		return;
> +
>  	if (dev_priv->backlight_level == 0)
>  		dev_priv->backlight_level = intel_panel_get_max_backlight(dev);
>  
> @@ -333,6 +339,9 @@ int intel_panel_setup_backlight(struct drm_device *dev)
>  	struct backlight_properties props;
>  	struct drm_connector *connector;
>  
> +	if (!i915_enable_backlight)
> +		return 0;
> +
>  	intel_panel_init_backlight(dev);
>  
>  	if (dev_priv->int_lvds_connector)
> @@ -368,6 +377,9 @@ void intel_panel_destroy_backlight(struct drm_device *dev)
>  #else
>  int intel_panel_setup_backlight(struct drm_device *dev)
>  {
> +	if (!i915_enable_backlight)
> +		return;
> +
>  	intel_panel_init_backlight(dev);
>  	return 0;
>  }
> -- 
> 1.7.5.4
> 
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-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48