Re: [PATCH v1] ARM: clocksource: make ARM_GLOBAL_TIMER selectable

[Robin Murphy]

On 26/04/16 20:35, Grygorii Strashko wrote:
> 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.

It sounds to me like the cleanest option might then be to address it 
within the Linux-specific driver itself. How feasible would it be for 
the GT driver to detect at runtime whether CPUfreq/idle will be used and 
simply refuse to register as a clocksource if so? (I guess there are 
probably horrible initialisation order issues, at least...)

Robin.

> > > - 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@xxxxxxxxxx>
> > > Cc: Florian Fainelli <f.fainelli@xxxxxxxxx>
> > > Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
> > > Cc: Wei Xu <xuwei5@xxxxxxxxxxxxx>
> > > Cc: Shawn Guo <shawnguo@xxxxxxxxxx>
> > > Cc: Sascha Hauer <kernel@xxxxxxxxxxxxxx>
> > > Cc: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxx>
> > > Cc: Maxime Coquelin <maxime.coquelin@xxxxxx>
> > > Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> > > Cc: Liviu Dudau <liviu.dudau@xxxxxxx>
> > > Cc: Sudeep Holla <sudeep.holla@xxxxxxx>
> > > Cc: Jun Nie <jun.nie@xxxxxxxxxx>
> > > Cc: Michal Simek <michal.simek@xxxxxxxxxx>
> > > Cc: Jesper Nilsson <jesper.nilsson@xxxxxxxx>
> > > Cc: Lars Persson <lars.persson@xxxxxxxx>
> > > Cc: Mike Looijmans <mike.looijmans@xxxxxxxx>
> > > Acked-by: SÃren Brinkmann <soren.brinkmann@xxxxxxxxxx>
> > > Acked-by: Moritz Fischer <moritz.fischer@xxxxxxxxx>
> > > Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
> > > ---
> > > 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
>
> [...]