linux-kernel - Re: [PATCH] clocksource: timer-atmel-pit: don't suspend/resume if unused

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Date:	Thu, 15 Jan 2015 12:41:27 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Nicolas Ferre <nicolas.ferre@...el.com>
CC:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Boris BREZILLON <boris.brezillon@...e-electrons.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	sylvain.rochet@...secur.com
Subject: Re: [PATCH] clocksource: timer-atmel-pit: don't suspend/resume if
 unused

On 01/13/2015 11:47 AM, Thomas Gleixner wrote:
> On Mon, 12 Jan 2015, Daniel Lezcano wrote:
>
>> On 01/12/2015 03:04 PM, Nicolas Ferre wrote:
>>> Le 18/12/2014 15:05, Nicolas Ferre a écrit :
>>>> From: Sylvain Rochet <sylvain.rochet@...secur.com>
>>>>
>>>> Waiting for PIT to stop counting takes a long time:
>>>>     1/(Master clock/prescaler/PIVR)
>>>> = 1/(133 MHz     /16       /2^20)
>>>> = 126 ms
>>>>
>>>> Up to 126 ms if master clock is set to 133 MHz, skipping suspend/resume
>>>> of the unused PIT device reduce (suspend time + resume time) from ~140 ms
>>>> to ~17 ms.
>>>>
>>>> Signed-off-by: Sylvain Rochet <sylvain.rochet@...secur.com>
>>>> [nicolas.ferre@...el.com: move to newer clocksource driver]
>>>> Signed-off-by: Nicolas Ferre <nicolas.ferre@...el.com>
>>>> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
>>>> ---
>>>> Hi Sylvain,
>>>>
>>>> I re-worked (and "Acked") your patch so it can be applied on the newer
>>>> Mainline
>>>> kernels. Beware, I changed the "subject line" as well. The PIT driver
>>>> moved
>>>> recently (3.18).
>>>>
>>>> Daniel,
>>>> Can you take this patch in your tree?
>>>
>>> Hi Daniel,
>>>
>>> Anything prevents this patch from being merged (aka ping ;-))?
>>
>> [Cc'ed tglx].
>>
>> Hi Nico,
>>
>> thanks for the head up.
>>
>> Nothing prevents it but I am wondering if this change shouldn't be in the
>> generic framework (kernel/time/clocksource.c and kernel/time/clockevents.c),
>> so all drivers will benefit this change ?
>
> Indeed. There is no point in calling suspend/resume for unused
> clockevents. They should be stopped and disabled already.

Hi Nico,

are you planning to do the change in the generic framework ?

Thanks
   -- Daniel

> Now with clocksources this might be different. We have no explicit
> state for this, but its trivial to add one at least for those
> clocksources which have enable/disable callbacks. For the other ones
> not so much.





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