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

[Hiroshi Doyu <hdoyu@nvidia.com>]

Marc Zyngier <marc.zyngier@arm.com> wrote @ Thu, 20 Dec 2012 13:05:45 +0100:

> On 20/12/12 11:57, Hiroshi Doyu wrote:
> > Marc Zyngier <marc.zyngier@arm.com> 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@nvidia.com>
> >>> ---
> >>>  .../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....
> 
> I appreciate this. But I expect this kernel to be also used on the
> non-secure side if someone tried to run KVM with it. And this would go
> bang right away.

What is the common way to make the above code selective at run
time(secure or non-secure path)?