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

Jani Nikula
2018-01-31T11:51:21Z

On Wed, 31 Jan 2018, Daniel Thompson <daniel.thompson@linaro.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@gmail.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@ti.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.

BR,
Jani.

>
> 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.
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--
Jani Nikula, Intel Open Source Technology Center