linux-kernel - Re: [PATCH AUTOSEL for 4.14 065/110] led: core: Fix brightness setting when setting delay

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Date:   Tue, 13 Mar 2018 08:50:22 +0100
From:   Pavel Machek <pavel@....cz>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Matthias Schiffer <mschiffer@...verse-factory.net>,
        Greg KH <gregkh@...uxfoundation.org>,
        Sasha Levin <Alexander.Levin@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Matthieu CASTET <matthieu.castet@...rot.com>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>
Subject: Re: [PATCH AUTOSEL for 4.14 065/110] led: core: Fix brightness
 setting when setting delay_off=0

Hi!

> > At least 7b6af2c531 ("leds: core: Fix regression caused by commit
> > 2b83ff96f51d") is missing, causing visible regressions (LEDs not working at
> > all) on some OpenWrt devices. This was fixed in 4.4.121 by reverting the
> > offending commit, but if I followed the discussion correctly, 4.9 should
> > get the follow-up commit 7b6af2c531 instead (like 4.14 already did).
> > 
> > Jacek's mail I replied to mentions that eb1610b4c273 ("led: core: Fix
> > blink_brightness setting race") should be included in 4.9 as well, but I
> > don't know the impact of the issue it fixes.
> 
> It doesn't fix any reported issue, but is just an improvement
> aiming at preventing potential races while changing blink brightness.
> 
> After taking closer look it turns out that for the patches in question
> to apply cleanly we need in 4.9 also a patch which introduces atomic
> bit fields for blink flags.
> 
> Effectively, here is the list of patches required in 4.9 stable:
> 
> Revert "led: core: Fix brightness setting when setting delay_off=0"
> 
> followed by:
> 
> a9c6ce57ec ("led: core: Use atomic bit-field for the blink-flags")
> eb1610b4c2 ("led: core: Fix blink_brightness setting race")
> 2b83ff96f5 ("led: core: Fix brightness setting when setting delay_off=0")
> 7b6af2c531 ("leds: core: Fix regression caused by commit 2b83ff96f51d")

For the record... there's no serious problem in LED subsystem in
v4.9. Just leave LED subsystem alone in v4.9-stable (reverting any
patches that were backported by some kind of bot that did not even
test them), and things will be fine.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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