Re: [PATCH v2 03/16] backlight: add backlight_is_blank()

[Daniel Thompson <daniel.thompson@linaro.org>]

On Sun, May 17, 2020 at 09:01:26PM +0200, Sam Ravnborg wrote:
> The backlight support has two properties that express the state:
> - power
> - state
> 
> It is un-documented and easy to get wrong.
> Add backlight_is_blank() helper to make it simpler for drivers
> to get the check of the state correct.
> 
> A lot of drivers also includes checks for fb_blank.
> This check is redundant when the state is checked
> and thus not needed in this helper function.
> But added anyway to avoid introducing subtle bug
> due to the creative use in some drivers.
> 
> Rolling out this helper to all relevant backlight drivers
> will eliminate almost all accesses to fb_blank.
> 
> v2:
>   - Added fb_blank condition (Daniel)
> 
> Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Lee Jones <lee.jones@linaro.org>
> Cc: Daniel Thompson <daniel.thompson@linaro.org>
> Cc: Jingoo Han <jingoohan1@gmail.com>

Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>


> ---
>  include/linux/backlight.h | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/include/linux/backlight.h b/include/linux/backlight.h
> index c7d6b2e8c3b5..a0a083b35c47 100644
> --- a/include/linux/backlight.h
> +++ b/include/linux/backlight.h
> @@ -175,6 +175,25 @@ static inline void backlight_put(struct backlight_device *bd)
>  		put_device(&bd->dev);
>  }
>  
> +/**
> + * backlight_is_blank - Return true if display is expected to be blank
> + * @bd: the backlight device
> + *
> + * Display is expected to be blank if any of these is true::
> + *
> + *   1) if power in not UNBLANK
> + *   2) if fb_blank is not UNBLANK
> + *   3) if state indicate BLANK or SUSPENDED
> + *
> + * Returns true if display is expected to be blank, false otherwise.
> + */
> +static inline bool backlight_is_blank(struct backlight_device *bd)
> +{
> +	return bd->props.power != FB_BLANK_UNBLANK ||
> +	       bd->props.fb_blank != FB_BLANK_UNBLANK ||
> +	       bd->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK);
> +}
> +
>  extern struct backlight_device *backlight_device_register(const char *name,
>  	struct device *dev, void *devdata, const struct backlight_ops *ops,
>  	const struct backlight_properties *props);
> -- 
> 2.25.1
> 
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