linux-kernel - Re: [PATCH v1] ARM: clocksource: make ARM_GLOBAL

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Message-ID: <20160427210641.GV5783@n2100.arm.linux.org.uk>
Date:	Wed, 27 Apr 2016 22:06:41 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Grygorii Strashko <grygorii.strashko@...com>
Cc:	Liviu Dudau <liviu.dudau@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
	linux-arm-kernel@...ts.infradead.org, Sekhar Nori <nsekhar@...com>,
	linux-omap@...r.kernel.org, Tony Lindgren <tony@...mide.com>,
	bcm-kernel-feedback-list@...adcom.com,
	linux-kernel@...r.kernel.org, linux-rockchip@...ts.infradead.org,
	kernel@...inux.com, linux-arm-kernel@...s.com,
	Florian Fainelli <f.fainelli@...il.com>,
	Wei Xu <xuwei5@...ilicon.com>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <kernel@...gutronix.de>,
	Srinivas Kandagatla <srinivas.kandagatla@...il.com>,
	Maxime Coquelin <maxime.coquelin@...com>,
	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	Sudeep Holla <sudeep.holla@....com>,
	Jun Nie <jun.nie@...aro.org>,
	Michal Simek <michal.simek@...inx.com>,
	Jesper Nilsson <jesper.nilsson@...s.com>,
	Lars Persson <lars.persson@...s.com>,
	Mike Looijmans <mike.looijmans@...ic.nl>
Subject: Re: [PATCH v1] ARM: clocksource: make ARM_GLOBAL_TIMER selectable

On Wed, Apr 27, 2016 at 04:31:05PM +0300, Grygorii Strashko wrote:
> Sorry, but this patch doesn't disable anything. It provides possibility
> to do a custom build with disabled ARM GT driver without Kernel code
> modification - in my case RT-kernel and non-RT Kernel should run on same
> HW and RT kernel should use ARM GT as clocksource/sched_clock, but 
> non-RT Kernel shouldn't.
> 
> I think RT can't be part of single zImage - it make no sense.
> 
> > 
> > Maybe a linux-specific property is needed here - "linux,low-power-unstable"
> > or something like that?
> > 
> 
> I've tried smth. like this [1]
> 
> And it is not "unstable", it's will just stop in C3 (CPUIdle) and there no possibility 
> (at least I've not found how to do this) to adjust Freq in case of CPUFreq.
> [above is about clocksource/sched_clock]
> 
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-November/386858.html

Don't think I'm going to follow URLs - I don't use a desktop mail
client, and as I'm several days behind with email, I don't have time
to go looking through a crappy pipermail web archive at the moment
either.

Anyway, why can't we use the priority system for clocksources?  If
ARM GT is problematical, we need a way to register it with a lower
priority than the preferred time keeping source.  That's exactly
what the clocksource priority field is for.

-- 
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
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