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: <20140106003714.GD27517@amd.pavel.ucw.cz>
Date:	Mon, 6 Jan 2014 01:37:14 +0100
From:	Pavel Machek <pavel@....cz>
To:	Bryan Wu <cooloney@...il.com>
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)

Hi!

> >> > 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.

That might be a bit too heavy. LED patterns do change quite often.

lp5523 driver uses this to push binary data through /sys. (It is code
for lp5523 processor in this case). Something like that would still be
better than firmware loader... 

cd /sys/class/i2c-adapter/i2c-2/2-0032 
echo load > engine1_mode 
echo cd /sys/class/i2c-adapter/i2c-2/2-0032 
echo 9d804000427f0d7f7f007f0042000000  > engine1_load 
echo run > engine1_mode
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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