linux-kernel - Re: [PATCH] led: ledtrig-transient: replace timer

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Message-ID: <20170424201829.GA18679@amd>
Date:   Mon, 24 Apr 2017 22:18:29 +0200
From:   Pavel Machek <pavel@....cz>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     David Lin <dtwlin@...gle.com>, rpurdie@...ys.net, robh@...nel.org,
        romlem@...gle.com, joelaf@...gle.com, stable@...r.kernel.org,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] led: ledtrig-transient: replace timer_list with hrtimer

Hi!
> Hi David,
> 
> Thanks for the patch.
> 
> Unfortunately we cannot switch to using hr timers just like that
> without introducing side effects for many devices. We had similar
> attempt of increasing timer tirgger accuracy two years ago [0].
> 
> In short words, for drivers that can sleep while setting brightness
> and/or are using a bus like I2C you will not be able to enforce
> 1ms delay period.
> 
> I recommend you to go through the thread [0] so that we had
> a well defined ground for the discussion on how to address this
> issue properly.
> 
> Alternatively, in order to avoid all quirks related to LED subsystem,
> I'd propose to implement this feature in the GPIO subsystem, which
> seems to be more suitable place for it.

Actually.. make that "implement it in force feedback subsystem where
it belongs". And we actually have force feedback subsystem, already,
see drivers/input/ff-core.c .

(Nokia N900 actually uses that subsystem for the vibration motor, so
there's existing code...)

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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