Re: [PATCH 5/9] clocksource: tegra: Enable ARM arch_timer with TSC

[Hiroshi Doyu]

Marc Zyngier <marc.zyngier@xxxxxxx> wrote @ Thu, 20 Dec 2012 12:01:15 +0100:

> On 20/12/12 09:44, Hiroshi Doyu wrote:
> > Add platform enabler for ARM arch_timer(TSC). TSC is more fine grained
> > timer than TMR0. If it's available, it will be used for clock source
> > and sched_clock. Otherwise, TMR0 is used. In any case TMR0 is
> > necessary for clock event.
> > 
> > Signed-off-by: Hiroshi Doyu <hdoyu@xxxxxxxxxx>
> > ---
> >  .../bindings/arm/tegra/nvidia,tegra114-tsc.txt     |   11 ++++
> >  drivers/clocksource/tegra20_timer.c                |   64 +++++++++++++++++++-
> >  2 files changed, 74 insertions(+), 1 deletion(-)
> >  create mode 100644 Documentation/devicetree/bindings/arm/tegra/nvidia,tegra114-tsc.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra114-tsc.txt b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra114-tsc.txt
> > new file mode 100644
> > index 0000000..9de936a
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra114-tsc.txt
> > @@ -0,0 +1,11 @@
> > +NVIDIA Tegra Timer Stamp Counter(TSC)
> > +
> > +Required properties:
> > +- compatible : "nvidia,tegra114-tsc
> > +- reg : Should contain 1 register ranges(address and length)
> > +
> > +Example:
> > +	tsc {
> > +		compatible = "nvidia,tegra114-tsc";
> > +		reg = <0x700f0000 0x20000>;
> > +	};
> > diff --git a/drivers/clocksource/tegra20_timer.c b/drivers/clocksource/tegra20_timer.c
> > index 1d25de8..285a6f1 100644
> > --- a/drivers/clocksource/tegra20_timer.c
> > +++ b/drivers/clocksource/tegra20_timer.c
> > @@ -30,6 +30,7 @@
> >  #include <asm/mach/time.h>
> >  #include <asm/smp_twd.h>
> >  #include <asm/sched_clock.h>
> > +#include <asm/arch_timer.h>
> >  
> >  #define RTC_SECONDS            0x08
> >  #define RTC_SHADOW_SECONDS     0x0c
> > @@ -271,10 +272,71 @@ static void __init tegra20_init_tmr(void)
> >  	clockevents_register_device(&tegra_clockevent);
> >  }
> >  
> > +#define TSC_CNTCR		0		/* TSC control registers */
> > +#define TSC_CNTCR_ENABLE	(1 << 0)	/* Enable */
> > +#define TSC_CNTCR_HDBG		(1 << 1)	/* Halt on debug */
> > +
> > +#define TSC_CNTCV0		0x8		/* TSC counter (LSW) */
> > +#define TSC_CNTCV1		0xc		/* TSC counter (MSW) */
> > +#define TSC_CNTFID0		0x20		/* TSC freq id 0 */
> > +
> > +static const struct of_device_id tegra_tsc_match[] __initconst = {
> > +	{ .compatible = "nvidia,tegra114-tsc" },
> > +	{}
> > +};
> > +
> > +static int tegra_arch_timer_init(void)
> > +{
> > +	int err;
> > +	struct device_node *np;
> > +	struct clk *clk;
> > +	void __iomem *tsc_base;
> > +	u32 freq, val;
> > +
> > +	np = of_find_matching_node(NULL, tegra_tsc_match);
> > +	if (!np)
> > +		return -ENODEV;
> > +
> > +	tsc_base = of_iomap(np, 0);
> > +	if (!tsc_base)
> > +		return -ENODEV;
> > +
> > +	clk = clk_get_sys("clk_m", NULL);
> > +	if (IS_ERR(clk)) {
> > +		freq = 12000000;
> > +		pr_warn("Unable to get timer clock. Assuming 12Mhz input clock.\n");
> > +	} else {
> > +		freq = clk_get_rate(clk);
> > +		clk_put(clk);
> > +	}
> > +	writel_relaxed(freq, tsc_base + TSC_CNTFID0);
> > +
> > +	/* CNTFRQ */
> > +	asm("mcr p15, 0, %0, c14, c0, 0\n" : : "r" (freq));
> > +	asm("mrc p15, 0, %0, c14, c0, 0\n" : "=r" (val));
> > +	BUG_ON(val != freq);
> 
> This is scary. CNTFRQ is only writable from secure mode, and will
> explode in any other situation.
> 
> Also, writing to CNTFRQ doesn't change the timer frequency! This is just
> a way for secure mode to tell the rest of the world the frequency the
> timer is ticking at. Unless you've wired the input clock to be able to
> change the frequency?

ATM, our upstream kernel is expected in secure mode. This situation
may be changed later, though....
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