Date: Wed, 27 Apr 2016 09:24:52 -0700
From: Tony Lindgren <tony@atomide.com>
To: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>,
        Liviu Dudau <liviu.dudau@arm.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>, Olof Johansson <olof@lixom.net>,
        linux-arm-kernel@lists.infradead.org, Sekhar Nori <nsekhar@ti.com>,
        linux-omap@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com,
        linux-kernel@vger.kernel.org, linux-rockchip@lists.infradead.org,
        kernel@stlinux.com, linux-arm-kernel@axis.com,
        Florian Fainelli <f.fainelli@gmail.com>, Wei Xu <xuwei5@hisilicon.com>,
        Shawn Guo <shawnguo@kernel.org>, Sascha Hauer <kernel@pengutronix.de>,
        Srinivas Kandagatla <srinivas.kandagatla@gmail.com>,
        Maxime Coquelin <maxime.coquelin@st.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Sudeep Holla <sudeep.holla@arm.com>, Jun Nie <jun.nie@linaro.org>,
        Michal Simek <michal.simek@xilinx.com>,
        Jesper Nilsson <jesper.nilsson@axis.com>,
        Lars Persson <lars.persson@axis.com>,
        Mike Looijmans <mike.looijmans@topic.nl>
Subject: Re: [PATCH v1] ARM: clocksource: make ARM_GLOBAL_TIMER selectable
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* Grygorii Strashko <grygorii.strashko@ti.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