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

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Date:	Wed, 27 Apr 2016 09:24:52 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Grygorii Strashko <grygorii.strashko@...com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	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, 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

* Grygorii Strashko <grygorii.strashko@...com> [160427 06:32]:
> Hi Russell,
> 
> On 04/27/2016 01:41 PM, Russell King - ARM Linux wrote:
> > On Tue, Apr 26, 2016 at 10:35:08PM +0300, Grygorii Strashko wrote:
> >> On 04/26/2016 07:02 PM, Liviu Dudau wrote:
> >>> Well, SoC-B has the GT *and* the DT node, so what is the problem with
> >>> enabling it for SoC-B? If there are reasons not to use the Global Timer
> >>> on SoC-B, surely a better option would be to mark it in DT with status = "disabled";
> >>
> >> This was rejected [2]. DT describes HW and if it is functional the status = "disabled"
> >> is not good choice.
> >> ARM GT can't be used as clocksource/sched_clock/clockevent when CPUFreq or
> >> CPUIdle are enabled :(, and this is Linux specific functionality and
> >> not HW description.
> > 
> > Sorry, but we don't want to have to disable drivers in the kernel just
> > because one platform has a problem (consider the single zImage case
> > where it may be required that the global timer is enabled for some
> > platform to boot - it becomes mandatory in single zImage at that point.)
> 
> 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.

How about a kernel cmdline option for both local timers to disable
the selected timer(s)?

Tony