linux-kernel - Re: [patch 2/5] MIPS: Dont select CLOCKSOURCE

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Message-ID: <87ms20d9jj.ffs@tglx>
Date: Mon, 26 Jan 2026 10:10:08 +0100
From: Thomas Gleixner <tglx@...nel.org>
To: "Maciej W. Rozycki" <macro@...am.me.uk>
Cc: LKML <linux-kernel@...r.kernel.org>, "Paul E. McKenney"
 <paulmck@...nel.org>, John Stultz <jstultz@...gle.com>, Waiman Long
 <longman@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Daniel
 Lezcano <daniel.lezcano@...aro.org>, Stephen Boyd <sboyd@...nel.org>,
 x86@...nel.org, "Gautham R. Shenoy" <gautham.shenoy@....com>, Jiri Wiesner
 <jwiesner@...e.de>, Daniel J Blueman <daniel@...ra.org>, Scott Hamilton
 <scott.hamilton@...den.com>, Helge Deller <deller@....de>,
 linux-parisc@...r.kernel.org, Thomas Bogendoerfer
 <tsbogend@...ha.franken.de>, linux-mips@...r.kernel.org
Subject: Re: [patch 2/5] MIPS: Dont select CLOCKSOURCE_WATCHDOG

On Sat, Jan 24 2026 at 22:28, Maciej W. Rozycki wrote:
> On Sat, 24 Jan 2026, Thomas Gleixner wrote:
>
>> MIPS selects CLOCKSOURCE_WATCHDOG, but none of the clocksources actually
>> sets the MUST_VERIFY flag. So compiling the watchdog in is a pointless
>> exercise. Remove the selects.
>
>  Based on commit 385864280597 ("mips: csrc-r4k: Mark R4K timer as unstable 
> if CPU freq changes") which added some of this stuff shouldn't the flag be 
> set instead?
>
>  At first glance the situation seems analogous to that of the x86 TSC: 
> just as the TSC the R4k timer is a CPU onchip free-running counter driven 
> by the CPU clock (typically at half the rate).

On x86 the CPU frequency can be modified by the BIOS behind the kernels
back, so the watchdog is required to catch this situation. So R4K only
needs the watchdog when there is some magic going on even when the
kernel itself does not manage the CPU frequency.

Thanks,

        tglx