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

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Date:   Mon, 5 Feb 2018 12:55:50 +0530
From:   Aishwarya Pant <aishpant@...il.com>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Milo Kim <milo.kim@...com>, linux-fbdev@...r.kernel.org,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Jingoo Han <jingoohan1@...il.com>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Julia Lawall <julia.lawall@...6.fr>,
        Greg KH <gregkh@...uxfoundation.org>,
        Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH 1/5] backlight: lp8788: document sysfs attributes

On Thu, Feb 01, 2018 at 11:36:04AM +0000, Daniel Thompson wrote:
> On Wed, Jan 31, 2018 at 01:51:21PM +0200, Jani Nikula wrote:
> > On Wed, 31 Jan 2018, Daniel Thompson <daniel.thompson@...aro.org> wrote:
> > > 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.
> > 
> > Agreed. I think the same holds for the other extra sysfs attributes. At
> > worst, having these prevents the backlight class from adding the names
> > later on, which is just backwards.
> 
> The problem is that they do exist...
> 
> For controls which appear to be misplaced debug attributes I think I am
> happy to nuke the values entirely. It is extremely improbable that any
> userspace will notice.
> 
> Unfortunately some of the controls look like they could be poked by an
> custom userspace so I'm quite so confident about nuking these ones...and if we
> don't nuke we should document (so thanks Aishwarya!). 
> 

Hi

Thanks for reviewing. Should I take it to assume that we would like to keep the
debug-like attributes in documentation for now?

Aishwarya

> 
> Daniel.