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: <20131229112101.GB26295@amd.pavel.ucw.cz>
Date:	Sun, 29 Dec 2013 12:21:01 +0100
From:	Pavel Machek <pavel@....cz>
To:	Greg KH <greg@...ah.com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Joe Xue <lgxue@...mail.com>,
	"cooloney@...il.com" <cooloney@...il.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!

> > 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?

Thanks,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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