linux-kernel - Re: [PATCH 1/6] backlight: Nuke unused backlight.props.state states

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Date:   Wed, 25 Apr 2018 15:42:15 -0400
From:   "Jingoo Han" <jingoohan1@...il.com>
To:     "'Daniel Vetter'" <daniel.vetter@...ll.ch>,
        "'DRI Development'" <dri-devel@...ts.freedesktop.org>,
        "'LKML'" <linux-kernel@...r.kernel.org>
Cc:     "'Lee Jones'" <lee.jones@...aro.org>,
        "'Daniel Thompson'" <daniel.thompson@...aro.org>,
        "'Meghana Madhyastha'" <meghana.madhyastha@...il.com>,
        "'Daniel Vetter'" <daniel.vetter@...el.com>
Subject: Re: [PATCH 1/6] backlight: Nuke unused backlight.props.state states

On Wednesday, April 25, 2018 1:43 PM, Daniel Vetter wrote:
> 
> The backlight power state handling is supremely confusing. We have:
> - props.power, using FB_BLANK_* defines
> - props.fb_blank, using the same, but deprecated int favour of
>   props.state
> - props.state, using the BL_CORE_* defines
> - and finally a bunch of backlight drivers treat brightness == 0 as
>   off. But of course not all of them.
> 
> This is way too much confusion to fix in a simple patch, but at least
> prevent more hilarity from spreading by removing the unused BL_CORE_*
> defines. I have no idea why exactly anyone would need that.
> 
> Wrt the ideal state, we really just want a boolean state. The 4 power
> saving states that the fbdev subsystem uses are overkill in todays hw
> (this was only relevant for VGA and similar analog circuits like
> TV-out), the new drm atomic modeset api simplified even the uapi to a
> simple bool. And there was never a valid technical reason to have the
> intermediate fbdev power states for backlights (those really only can
> be either off or on).
> 
> Cleanup motivated by Meghana's questions about all this.
> 
> Cc: Lee Jones <lee.jones@...aro.org>
> Cc: Daniel Thompson <daniel.thompson@...aro.org>
> Cc: Jingoo Han <jingoohan1@...il.com>
> Cc: Meghana Madhyastha <meghana.madhyastha@...il.com>
> Acked-by: Daniel Thompson <daniel.thompson@...aro.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>

Acked-by: Jingoo Han <jingoohan1@...il.com>

I really love this patch!
Good job!
Thank you.

Best regards,
Jingoo Han

> ---
>  include/linux/backlight.h | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/include/linux/backlight.h b/include/linux/backlight.h
> index 2baab6f3861d..1db67662bfcb 100644
> --- a/include/linux/backlight.h
> +++ b/include/linux/backlight.h
> @@ -84,9 +84,6 @@ struct backlight_properties {
> 
>  #define BL_CORE_SUSPENDED	(1 << 0)	/* backlight is suspended */
>  #define BL_CORE_FBBLANK		(1 << 1)	/* backlight is
under an fb
> blank event */
> -#define BL_CORE_DRIVER4		(1 << 28)	/* reserved for
driver
> specific use */
> -#define BL_CORE_DRIVER3		(1 << 29)	/* reserved for
driver
> specific use */
> -#define BL_CORE_DRIVER2		(1 << 30)	/* reserved for
driver
> specific use */
>  #define BL_CORE_DRIVER1		(1 << 31)	/* reserved for
driver
> specific use */
> 
>  };
> --
> 2.17.0