linux-kernel - Re: how to represent sequence of brightnesses in /sys (was Re: [PATCH] Add the LED burst trigger)

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Message-ID: <CAK5ve-LOFE6h5w=+pSgfYMaW5GZQfayVfpRzP0NAfMPWZkk5iw@mail.gmail.com>
Date:	Thu, 2 Jan 2014 16:16:38 -0800
From:	Bryan Wu <cooloney@...il.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Greg KH <greg@...ah.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Joe Xue <lgxue@...mail.com>,
	"rpurdie@...ys.net" <rpurdie@...ys.net>,
	"rob@...dley.net" <rob@...dley.net>,
	"milo.kim@...com" <milo.kim@...com>,
	"linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: how to represent sequence of brightnesses in /sys (was Re:
 [PATCH] Add the LED burst trigger)

On Sun, Dec 29, 2013 at 3:21 AM, Pavel Machek <pavel@....cz> wrote:
> Hi!
>
>> > Idea would be "sequence of brigtnesses" (one file) and "delay between
>> > changes" (second file).
>>
>> Ick.
>>
>> > Reason to do it in kernel is that some machines actually have
>> > "coprocessor" on i2c that can do it while main CPU is suspended. (For
>> > more reasons, see beggining of thread).
>>
>> Ick ick.
>>
>> > Binary attribute with array of bytes should be acceptable, rights?
>>
>> Not at all.
>>
>> > (IOW write(..., buf, size) )
>> >
>> > Ascii array of decimal integers -- no so, right?
>> >
>> > (IOW printf("%d %d ..", buf[0], buf[1]) )
>>
>> Use an ioctl with a structure to get things correct as a character
>> device.  As odds are, you aren't going to be able to create a "generic"
>> format for all of this for all types of devices that support such a
>> "co-processor".
>
> Well, we already do have hw-specific driver in the tree,
> drivers/leds/leds-lp55xx-common.c . But the interface is
> "interesting" and I believe we should have generic interface and it
> should use existing trigger framework -- array of brightnesses does
> not seem too complicated.
>
> Do you have suggestion how to pass the brightnesses over sysfs?
>

What about send those binary stuff as firmware through kernel firmware
interface and LED trigger sysfs is just for parameters setup and
enable/disable controlling.

Thanks,
-Bryan
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