[Intel-gfx] [PATCHv2] drm/i915/display: add support for dual panel backlight

[Jani Nikula]

On Wed, 13 Jul 2022, Arun R Murthy <arun.r.murthy at intel.com> wrote:
> The patch with commit 20f85ef89d94 ("drm/i915/backlight: use unique
> backlight device names") already adds support for dual panel backlight
> but with error prints. Since the patch tried to create the backlight
> device with the same name and upon failure will try with a different
> name it leads to failure logs in dmesg inturn getting caught by CI.
>
> This patch alternately will check if the backlight class of same name
> exists, will use a different name.
>
> v2: reworked on top of the patch 20f85ef89d94 ("drm/i915/backlight: use
> unique backlight device names")
>
> Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
> ---
>  .../gpu/drm/i915/display/intel_backlight.c    | 24 ++++++++-----------
>  1 file changed, 10 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_backlight.c b/drivers/gpu/drm/i915/display/intel_backlight.c
> index 110fc98ec280..1e550d048e86 100644
> --- a/drivers/gpu/drm/i915/display/intel_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_backlight.c
> @@ -971,26 +971,22 @@ int intel_backlight_device_register(struct intel_connector *connector)
>  	if (!name)
>  		return -ENOMEM;
>  
> -	bd = backlight_device_register(name, connector->base.kdev, connector,
> -				       &intel_backlight_device_ops, &props);
> -
> -	/*
> -	 * Using the same name independent of the drm device or connector
> -	 * prevents registration of multiple backlight devices in the
> -	 * driver. However, we need to use the default name for backward
> -	 * compatibility. Use unique names for subsequent backlight devices as a
> -	 * fallback when the default name already exists.
> -	 */
> -	if (IS_ERR(bd) && PTR_ERR(bd) == -EEXIST) {
> +	if (backlight_device_get_by_name(name)) {

This leaks a reference count to the backlight device. It needs to be
something like:

	bd = backlight_device_get_by_name(name);
	if (bd) {
		put_device(&bd->dev);

		/* ... */
	}

BR,
Jani.

> +		/*
> +		 * Using the same name independent of the drm device or connector
> +		 * prevents registration of multiple backlight devices in the
> +		 * driver. However, we need to use the default name for backward
> +		 * compatibility. Use unique names for subsequent backlight devices as a
> +		 * fallback when the default name already exists.
> +		 */
>  		kfree(name);
>  		name = kasprintf(GFP_KERNEL, "card%d-%s-backlight",
>  				 i915->drm.primary->index, connector->base.name);
>  		if (!name)
>  			return -ENOMEM;
> -
> -		bd = backlight_device_register(name, connector->base.kdev, connector,
> -					       &intel_backlight_device_ops, &props);
>  	}
> +	bd = backlight_device_register(name, connector->base.kdev, connector,
> +				       &intel_backlight_device_ops, &props);
>  
>  	if (IS_ERR(bd)) {
>  		drm_err(&i915->drm,

-- 
Jani Nikula, Intel Open Source Graphics Center