linux-kernel - Re: [PATCH/RFC] arm: arch_timer: Do not set C3STOP in case CPU

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Message-ID: <20130617025704.GA27933@verge.net.au>
Date:	Mon, 17 Jun 2013 11:57:05 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	Magnus Damm <magnus.damm@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Mark Rutland <mark.rutland@....com>,
	SH-Linux <linux-sh@...r.kernel.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	John Stultz <john.stultz@...aro.org>,
	Shinya Kuribayashi <shinya.kuribayashi.px@...esas.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH/RFC] arm: arch_timer: Do not set C3STOP in case CPU_IDLE=n

On Mon, Jun 17, 2013 at 11:47:11AM +0900, Magnus Damm wrote:
> Hi Simon,
> 
> On Mon, Jun 17, 2013 at 11:13 AM, Simon Horman <horms@...ge.net.au> wrote:
> > On Mon, Jun 17, 2013 at 09:20:56AM +0900, Magnus Damm wrote:
> >> From: Magnus Damm <damm@...nsource.se>
> >>
> >> Modify the ARM architected timer driver to not set C3STOP
> >> in case CPU_IDLE is disabled. This is a short term fix that
> >> allows use of high resolution timers even though no additional
> >> clock event is registered.
> >>
> >> Not-really-Signed-off-by: Magnus Damm <damm@...nsource.se>
> >> ---
> >>
> >>  If someone cares about this case then perhaps it should be
> >>  moved up to the clock event main code. The same issue should
> >>  in theory trigger on all architectures, perhaps x86 people
> >>  hunting for low latency may try to disable CPU_IDLE?
> >>
> >>  I propose carrying this patch locally to enable high resolution
> >>  timers until CPU_IDLE and an additional clock event is supported.
> >>
> >>  Observed on r8a73a4 and APE6EVM.
> >
> > Hi Magnus,
> >
> > Is this patch intended to be picked up by me for the LTSI-3.4.25 based
> > backports that live in my renesas-backports tree?
> 
> Yes, correct.
> 
> The patch was mainly written to satisfy a feature request for your
> backports, but I noticed that the same issue exists in upstream as
> well.
> 
> Ideally I'd like to use the same code for the backport and upstream,
> but I am not sure if anyone in upstream really cares. The more long
> term solution is obviously to install a second clock event, perhaps
> that's good enough.
> 
> > If so, could you  clearly state this (below the '---' is fine) and
> > include a proper Sob line to indicate that it is fit to be merged
> > even if that merge is not into mainline.
> 
> Sure, but  I'd like to hear opinions from other people before
> resending. I will follow your recommendation in next version.

Thanks, I understand. I'll wait for discussion and a new version.
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