linux-kernel - Re: [PATCH] clocksource: arch_timer: Allow the device tree to specify the physical timer

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Date:	Thu, 11 Sep 2014 17:09:08 +0100
From:	Will Deacon <will.deacon@....com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Christopher Covington <cov@...eaurora.org>,
	Olof Johansson <olof@...om.net>,
	Mark Rutland <Mark.Rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Pawel Moll <Pawel.Moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Sudeep Holla <Sudeep.Holla@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Kumar Gala <galak@...eaurora.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sonny Rao <sonnyrao@...omium.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Nathan Lynch <Nathan_Lynch@...tor.com>
Subject: Re: [PATCH] clocksource: arch_timer: Allow the device tree to
 specify the physical timer

On Thu, Sep 11, 2014 at 05:04:11PM +0100, Doug Anderson wrote:
> On Thu, Sep 11, 2014 at 8:58 AM, Christopher Covington
> <cov@...eaurora.org> wrote:
> > On 09/11/2014 11:52 AM, Doug Anderson wrote:
> >> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> >> index 5163ec1..8ca07a9 100644
> >> --- a/drivers/clocksource/arm_arch_timer.c
> >> +++ b/drivers/clocksource/arm_arch_timer.c
> >> @@ -649,6 +649,9 @@ static void __init arch_timer_init(struct device_node *np)
> >>               arch_timer_ppi[i] = irq_of_parse_and_map(np, i);
> >>       arch_timer_detect_rate(NULL, np);
> >>
> >> +     if (of_property_read_bool(np, "arm,use-physical-timer"))
> >> +             arch_timer_use_virtual = false;

Can you #ifdef CONFIG_ARM here please?

> >>       /*
> >>        * If HYP mode is available, we know that the physical timer
> >>        * has been configured to be accessible from PL1. Use it, so
> >>
> >
> > How's the VDSO supposed to deal with this? It currently does:
> >
> > cycle_now = arch_counter_get_cntvct()
> 
> I don't see that line of code anywhere when I do a "git grep" on linux
> or linuxnext.  Can you give me a clearer pointer?

It's in the actual vdso code (arch/arm64/kernel/vdso/gettimeofday.S):

	/* Read the virtual counter. */
	isb
	mrs	x15, cntvct_el0

Will
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