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

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Message-ID: <CANqRtoTfiWFv0JWwJysi47gsSjJx9g3-FFMMzCYROWDPbndnYQ@mail.gmail.com>
Date:	Mon, 17 Jun 2013 11:47:11 +0900
From:	Magnus Damm <magnus.damm@...il.com>
To:	Simon Horman <horms@...ge.net.au>
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

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,

/ magnus
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