linux-kernel - Re: [PATCH 1/5] backlight: lp8788: document sysfs attributes

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Message-ID: <20180131110727.rmmwyqzwozwhda6z@oak.lan>
Date:   Wed, 31 Jan 2018 11:07:27 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Aishwarya Pant <aishpant@...il.com>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Greg KH <gregkh@...uxfoundation.org>,
        Milo Kim <milo.kim@...com>, Julia Lawall <julia.lawall@...6.fr>
Subject: Re: [PATCH 1/5] backlight: lp8788: document sysfs attributes

On Fri, Jan 26, 2018 at 08:20:08PM +0530, Aishwarya Pant wrote:
> Add documentation for sysfs interfaces of lp8788 backlight driver by
> looking through the code and the git commit history.
> 
> Signed-off-by: Aishwarya Pant <aishpant@...il.com>
> ---
>  Documentation/ABI/testing/sysfs-class-backlight-lp8788 | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-class-backlight-lp8788
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-backlight-lp8788 b/Documentation/ABI/testing/sysfs-class-backlight-lp8788
> new file mode 100644
> index 000000000000..c0e565c8d63d
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-class-backlight-lp8788
> @@ -0,0 +1,10 @@
> +sysfs interface for Texas Instruments lp8788 mfd backlight driver
> +-----------------------------------------------------------------
> +
> +What:		/sys/class/backlight/<backlight>/bl_ctl_mode
> +Date:		Feb, 2013
> +KernelVersion:	v3.10
> +Contact:	Milo Kim <milo.kim@...com>
> +Description:
> +		(RO) Displays whether the brightness is controlled by the PWM
> +		input("PWM based") or the I2C register("Register based").

I rather dislike drivers with this type of "bonus" sysfs controls. I'm
struggling to come up with any reason why the userspace would want to
read this control (and I think bl_ctl_mode gets the fewest hits after
searching with google hits of any search I've tried) . It looks to me 
like this is debug information that should never have gone into sysfs 
at all.

So I think this is either something that should go directly into
ABI/obsolete (with a fairly short expiry time) or perhaps simply
remove the property entirely.


Daniel.