linux-kernel - Re: PROBLEM: hwclock busted w/ M48T59 RTC (regression)

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Message-ID: <f60b787529422eb2b3655b92aa8a7377b838baf4.camel@physik.fu-berlin.de>
Date: Wed, 26 Nov 2025 10:46:37 +0100
From: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To: Nick Bowler <nbowler@...conx.ca>, linux-kernel@...r.kernel.org, 
	regressions@...ts.linux.dev, linux-rtc@...r.kernel.org
Cc: Esben Haabendal <esben@...nix.com>, stable@...r.kernel.org, 
	sparclinux@...r.kernel.org, regressions <regressions@...ts.linux.dev>
Subject: Re: PROBLEM: hwclock busted w/ M48T59 RTC (regression)

Hi Nick,

I have not used the regression tracker before, so let's give it a try:

#regzbot ^introduced: 795cda8338eab036013314dbc0b04aae728880ab

Adrian

On Tue, 2025-11-25 at 22:18 -0500, Nick Bowler wrote:
> Any thoughts?
> 
> The problem is still present in 6.18-rc7 and reverting the commit
> indicated below still fixes it.
> 
> I am also seeing the same failure on a totally different system with
> Dallas DS1286 RTC, which is also fixed by reverting this commit.
> 
> Since the initial report this regression has been further backported
> to all the remaining longterm kernel series.
> 
> Thanks,
>   Nick
> 
> On Thu, Oct 23, 2025 at 12:45:13AM -0400, Nick Bowler wrote:
> > Hi,
> > 
> > After a stable kernel update, the hwclock command seems no longer
> > functional on my SPARC system with an ST M48T59Y-70PC1 RTC:
> > 
> >   # hwclock
> >   [...long delay...]
> >   hwclock: select() to /dev/rtc0 to wait for clock tick timed out
> > 
> > On prior kernels, there is no problem:
> > 
> >   # hwclock
> >   2025-10-22 22:21:04.806992-04:00
> > 
> > I reproduced the same failure on 6.18-rc2 and bisected to this commit:
> > 
> >   commit 795cda8338eab036013314dbc0b04aae728880ab
> >   Author: Esben Haabendal <esben@...nix.com>
> >   Date:   Fri May 16 09:23:35 2025 +0200
> >   
> >       rtc: interface: Fix long-standing race when setting alarm
> > 
> > This commit was backported to all current 6.x stable branches,
> > as well as 5.15.x, so they all have the same regression.
> > 
> > Reverting this commit on top of 6.18-rc2 corrects the problem.
> > 
> > Let me know if you need any more info!
> > 
> > Thanks,
> >   Nick

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
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