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

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Date:	Tue, 26 Apr 2016 22:35:08 +0300
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Liviu Dudau <liviu.dudau@....com>
CC:	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>,
	Russell King <linux@....linux.org.uk>,
	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 04/26/2016 07:02 PM, Liviu Dudau wrote:
> On Tue, Apr 26, 2016 at 06:28:52PM +0300, Grygorii Strashko wrote:
> 
> Hi Grygorii,
> 
> First time I'm seeing this patch, so I have a few questions, mostly
> related to the commit message:

Hm. You are in cc for RFC.
Sry, forgot to add link [1].

> 
>> This patch intended to fix following cases:
>> - SoC-A has ARM GT, defines DT node for ARM GT and selects
>> ARM_GLOBAL_TIMER statically in Kconfig file. SoC-B has ARM GT and
>> defines DT node for ARM GT, but do not selects ARM_GLOBAL_TIMER
>> statically in Kconfig file. In case of multiplatform build ARM GT will
>> be implicitly enabled for SoC-B.
> 
> 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. 

> 
>>
>> - There is no way to disable ARM GT without modifying Kconfig file,
>> once ARM_GLOBAL_TIMER is selected statically in Kconfig file.
> 
> What about disabling the DT node?
> 
> Not sure I properly understand the problem you are trying to solve here.

I'd like to have way to enable/disable ARM GT without modifying Kernel sources
(Kconfig specifically) which is now impossible.

> 
>>
>> Hence, fix above case by defining both HAVE_ARM_GLOBAL_TIMER and
>> ARM_GLOBAL_TIMER as recommended by 'Adding common features and make
>> the usage configurable' section in kconfig-language.txt. All places in
>> ARM folder where ARM_GLOBAL_TIMER was used now replaced on
>> HAVE_ARM_GLOBAL_TIMER.
> 
> I'm OK with the way you have changed ARM_GLOBAL_TIMER from a sticky config
> option to a selectable one, but I would like more details on the problem
> this was causing you.
> 

The same HW (board) could be used with PM features enabled (power saving)
and disabled (-RT). Without this change it will require to have
and maintain two branches, but with it - just separate defconfig.

[1] http://lists.infradead.org/pipermail/linux-rockchip/2016-February/007159.html
[2] http://www.spinics.net/lists/devicetree/msg102918.html

> 
>>
>> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
>> Cc: Florian Fainelli <f.fainelli@...il.com>
>> Cc: Russell King <linux@....linux.org.uk>
>> Cc: Wei Xu <xuwei5@...ilicon.com>
>> Cc: Shawn Guo <shawnguo@...nel.org>
>> Cc: Sascha Hauer <kernel@...gutronix.de>
>> Cc: Srinivas Kandagatla <srinivas.kandagatla@...il.com>
>> Cc: Maxime Coquelin <maxime.coquelin@...com>
>> Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
>> Cc: Liviu Dudau <liviu.dudau@....com>
>> Cc: Sudeep Holla <sudeep.holla@....com>
>> Cc: Jun Nie <jun.nie@...aro.org>
>> Cc: Michal Simek <michal.simek@...inx.com>
>> Cc: Jesper Nilsson <jesper.nilsson@...s.com>
>> Cc: Lars Persson <lars.persson@...s.com>
>> Cc: Mike Looijmans <mike.looijmans@...ic.nl>
>> Acked-by: Sören Brinkmann <soren.brinkmann@...inx.com>
>> Acked-by: Moritz Fischer <moritz.fischer@...us.com>
>> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
>> ---
>> Changes is v1:
>> - updated mach-artpec
>> - rebased on top of tip: timers/core
>>    commit: 86d3473 time: Introduce do_sys_settimeofday64()
>>
>>   arch/arm/mach-artpec/Kconfig   | 2 +-
>>   arch/arm/mach-bcm/Kconfig      | 4 ++--
>>   arch/arm/mach-hisi/Kconfig     | 2 +-
>>   arch/arm/mach-imx/Kconfig      | 2 +-
>>   arch/arm/mach-rockchip/Kconfig | 2 +-
>>   arch/arm/mach-sti/Kconfig      | 2 +-
>>   arch/arm/mach-uniphier/Kconfig | 2 +-
>>   arch/arm/mach-vexpress/Kconfig | 2 +-
>>   arch/arm/mach-zx/Kconfig       | 2 +-
>>   arch/arm/mach-zynq/Kconfig     | 2 +-
>>   drivers/clocksource/Kconfig    | 7 ++++++-
>>   11 files changed, 17 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/arm/mach-artpec/Kconfig b/arch/arm/mach-artpec/Kconfig
>> index 6cbe5a2..6cbca77 100644
>> --- a/arch/arm/mach-artpec/Kconfig
>> +++ b/arch/arm/mach-artpec/Kconfig
>> @@ -9,7 +9,7 @@ config MACH_ARTPEC6
>>   	depends on ARCH_MULTI_V7
>>   	select ARM_AMBA
>>   	select ARM_GIC
>> -	select ARM_GLOBAL_TIMER

[...]

-- 
regards,
-grygorii