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

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Message-ID: <20180313132748.GA20246@amd>
Date:   Tue, 13 Mar 2018 14:27:48 +0100
From:   Pavel Machek <pavel@....cz>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Matthias Schiffer <mschiffer@...verse-factory.net>,
        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")
> 
> Odd, I just got another report that the 4.9.87 release fixed some
> reported LED issues, so why do I need all of these?
> 
> Should I just revert the single 2b83ff96f51d commit here instead?

I believe so, yes.

I'm not aware of any _really bad_ issues with LED subsystem in
4.9. Take a look at changelog of
2b83ff96f51d0b039c4561b9f95c824d7bddb85c -- it fixes rather
theoretical issue; user can reproduce it by hand in shell, but,
well... don't do it then.

The rest of fixes ... fix some more theoretical races. I don't think
it is -stable material, as I pointed out before.

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

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