linux-kernel - Re: [PATCH] leds: Introduce userspace leds driver

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Date:   Thu, 15 Sep 2016 16:53:39 +0200
From:   Jacek Anaszewski <j.anaszewski@...sung.com>
To:     Pavel Machek <pavel@....cz>
Cc:     David Lechner <david@...hnology.com>,
        Richard Purdie <rpurdie@...ys.net>,
        linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org,
        Marcel Holtmann <marcel@...tmann.org>
Subject: Re: [PATCH] leds: Introduce userspace leds driver

Hi Pavel,

On 09/15/2016 02:41 PM, Pavel Machek wrote:
> Hi!
>
>> Thanks for the patch. It is very nice. I have only one minor remark
>> in the code.
>>
>> I think that it would be good to add a documentation for this
>> driver to Documentation/leds, with exemplary C program instead
>> of python one. The program could poll the dev node in a loop,
>> which allows to conveniently check the impact of setting particular
>> triggers and all other brightness change events.
>
> Actually, I'd say that python is fine -- it is used heavily in tools/.
>
> But perhaps the example program should go to tools/?

I see python scripts only in perf tools. Let's stay by C application.

David, could you please prepare another version of the patch, that
splits test app code to the separate file in tools/leds (the directory
doesn't exist so far), also providing suitable Makefile?

>>> def change_brightness(b):
>>>    with open('/sys/class/leds/{}/brightness'.format(name) , 'w') as f:
>>>       f.write(str(b))
>>>
>>>
>>> with open('/dev/uleds', 'rb+', 0) as uleds:
>>>    bname = name.encode("ascii")
>>>    # create the leds class device
>>>    uleds.write(bname + b'\0' * (ULEDS_MAX_NAME_SIZE - len(bname)))
>
> Umm. I don't see it in the kernel code. You let userspace provide a
> LED name?
>
> Where is the LED name tested for sanity? I guess there could be a lot
> of fun naming a led ".." for example...

Good point.

-- 
Best regards,
Jacek Anaszewski