linux-kernel - Re: [RFC part3 PATCH 2/2] ARM64 / clocksource: Use arch_timer_acpi

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Date:	Mon, 9 Dec 2013 10:37:43 -0800
From:	Olof Johansson <olof@...om.net>
To:	Hanjun Guo <hanjun.guo@...aro.org>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Grant Likely <grant.likely@...aro.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Rob Herring <rob.herring@...xeda.com>,
	Mark Rutland <mark.rutland@....com>,
	Jon Masters <jonathan@...masters.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Patch Tracking <patches@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>
Subject: Re: [RFC part3 PATCH 2/2] ARM64 / clocksource: Use
 arch_timer_acpi_init()

On Tue, Dec 03, 2013 at 09:52:30PM +0800, Hanjun Guo wrote:
> On 2013年12月03日 20:27, Linus Walleij wrote:
> >On Tue, Dec 3, 2013 at 12:15 PM, Hanjun Guo <hanjun.guo@...aro.org> wrote:
> >
> >>+       /* if can't be initialised from DT, try ACPI way */
> >>+       if (!arch_timer_get_rate())
> >>+               arch_timer_acpi_init();
> >>+
> >>         arch_timer_rate = arch_timer_get_rate();
> >This looks a bit fragile. Having a call like arch_timer_get_rate()
> >to check whether there is a DT node for the timer doesn't seem
> >right, can you refactor the code to provide some
> >has_arch_timer_node() or similar call instead, so it's a bit easier
> >to understand & maintain at least?
> 
> Good point, thanks for the guidance.
> I will introduce has_arch_timer_node() as you said and use
> it as follows:
> 
> if (has_arch_timer_node())
> clocksource_of_init();
> esle
> arch_timer_acpi_init(); /* try ACPI way */
> 
> Is this make sense to you?

Even when we boot with ACPI, the boot stub will still create a minimal
DTB. We should just make sure that the clocksource (which will be
architectured timers anyway, I believe?) is described in that stub.

I would rather do that than have dual-path booting in the lowlevel setup, it
increases test requirements and makes it hard for someone without ACPI hardware
to check for regressions in this code, etc.


-Olof
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