linux-kernel - Re: [PATCH 2/2] arm64: dts: mt8173: add timer node

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Message-ID: <560D5227.8050600@arm.com>
Date:	Thu, 1 Oct 2015 16:32:55 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	Yingjoe Chen <yingjoe.chen@...iatek.com>
Cc:	Sudeep Holla <sudeep.holla@....com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Michael Turquette <mturquette@...libre.com>,
	James Liao <jamesjj.liao@...iatek.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	"linux-mediatek@...ts.infradead.org" 
	<linux-mediatek@...ts.infradead.org>,
	Sascha Hauer <kernel@...gutronix.de>,
	Olof Johansson <olof@...om.net>,
	"srv_heupstream@...iatek.com" <srv_heupstream@...iatek.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Daniel Kurtz <djkurtz@...omium.org>,
	"linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
	Eddie Huang <eddie.huang@...iatek.com>
Subject: Re: [PATCH 2/2] arm64: dts: mt8173: add timer node



On 01/10/15 15:33, Yingjoe Chen wrote:
> On Thu, 2015-09-17 at 17:13 +0100, Sudeep Holla wrote:
>>

[...]

>>
>> I think your are confusing the system counter with arch timers. System
>> counter is always-on, but the arch timers(logic implementing timers
>> comparators) might not be off when the processor is powered down.
>>
>> I think you need this timer and are using it for low power idle states
>> in which case you will use this as a clock event and not clock source.
>> It will be used as a hardware broadcast event source.
>>
>> There's no call to sched_clock_register in mtk_timer.c, so it can't be
>> the sched clock, so you need to fix the commit log.
>
> Hi Sudeep,
>
> Sorry for late reply.
>
> For sched_clock_register, please see
> http://lists.infradead.org/pipermail/linux-mediatek/2015-July/001547.html
> which was accepted in
> https://git.linaro.org/people/daniel.lezcano/linux.git/shortlog/refs/heads/clockevents/4.4
>

The commit message makes no sense to me. The counters should continue to
work as long as they are in always-on domain. Only timers are lost
when you enter deeper idle states. So I agree with using MTK timer as
broadcast timer/eventsource. You still didn't answer what's the need
to use MTK timer as sched clocksource ?

Regards,
Sudeep
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