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

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Message-ID: <gfwdg244bcmkv7l44fknfi4osd2b23unwaos7rnlirkdy2rrrt@yovd2vewdviv>
Date: Tue, 25 Nov 2025 22:18:10 -0500
From: Nick Bowler <nbowler@...conx.ca>
To: 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
Subject: Re: PROBLEM: hwclock busted w/ M48T59 RTC (regression)

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