linux-kernel - Re: [PATCH v7 05/12] clocksource: mips-gic-timer: Always use cluster 0 counter as clocksource

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Message-ID: <Zx+qrRVdv5EGXbCF@alpha.franken.de>
Date: Mon, 28 Oct 2024 16:15:57 +0100
From: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: Aleksandar Rikalo <arikalo@...il.com>, Chao-ying Fu <cfu@...ecomp.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Greg Ungerer <gerg@...nel.org>, Hauke Mehrtens <hauke@...ke-m.de>,
	Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>,
	Jiaxun Yang <jiaxun.yang@...goat.com>, linux-kernel@...r.kernel.org,
	linux-mips@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
	Paul Burton <paulburton@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Serge Semin <fancer.lancer@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tiezhu Yang <yangtiezhu@...ngson.cn>,
	Gregory CLEMENT <gregory.clement@...tlin.com>
Subject: Re: [PATCH v7 05/12] clocksource: mips-gic-timer: Always use cluster
 0 counter as clocksource

On Mon, Oct 28, 2024 at 03:54:48PM +0100, Daniel Lezcano wrote:
> On 19/10/2024 09:10, Aleksandar Rikalo wrote:
> > From: Paul Burton <paulburton@...nel.org>
> > 
> > In a multi-cluster MIPS system, there are multiple GICs - one in each
> > cluster - each of which has its independent counter. The counters in
> > each GIC are not synchronized in any way, so they can drift relative
> > to one another through the lifetime of the system. This is problematic
> > for a clock source which ought to be global.
> > 
> > Avoid problems by always accessing cluster 0's counter, using
> > cross-cluster register access. This adds overhead so it is applied only
> > on multi-cluster systems.
> > 
> > Signed-off-by: Paul Burton <paulburton@...nel.org>
> > Signed-off-by: Chao-ying Fu <cfu@...ecomp.com>
> > Signed-off-by: Dragan Mladjenovic <dragan.mladjenovic@...mia.com>
> > Signed-off-by: Aleksandar Rikalo <arikalo@...il.com>
> > Tested-by: Serge Semin <fancer.lancer@...il.com>
> > ---
> 
> May I take this patch through the clocksource tree ?

sure, should be the best option.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]