Re: [PATCH/RFC] arm: arch_timer: Do not set C3STOP in case CPU_IDLE=n

From: Magnus Damm
Date: Sun Jun 16 2013 - 22:47:19 EST


Hi Simon,

On Mon, Jun 17, 2013 at 11:13 AM, Simon Horman <horms@xxxxxxxxxxxx> wrote:
> On Mon, Jun 17, 2013 at 09:20:56AM +0900, Magnus Damm wrote:
>> From: Magnus Damm <damm@xxxxxxxxxxxxx>
>>
>> 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@xxxxxxxxxxxxx>
>> ---
>>
>> 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/