From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marc Zyngier <marc.zyngier-5wv7dgnIgG8@public.gmane.org>
Subject: Re: [v2 5/9] clocksource: tegra: Enable ARM arch_timer with TSC
Date: Tue, 08 Jan 2013 16:07:39 +0000
Message-ID: <50EC444B.5060206@arm.com>
References: <1357649263-1098-1-git-send-email-hdoyu@nvidia.com> <1357649263-1098-6-git-send-email-hdoyu@nvidia.com>
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To: Hiroshi Doyu <hdoyu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
Cc: "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" <linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>
List-Id: linux-tegra@vger.kernel.org

On 08/01/13 12:47, 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-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
> ---
>  .../bindings/arm/tegra/nvidia,tegra114-tsc.txt     |   11 ++++
>  drivers/clocksource/tegra20_timer.c                |   65 +++++++++++++++++++-
>  2 files changed, 75 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..564266d 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 +272,72 @@ 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" },
> +	{}
> +};
> +
> +/* FIXME: only secure mode is supported. */

And this is a bug, as far as I'm concerned.

> +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);

No, not again! Like I said last year, this won't fly. So instead of
trying to work around a broken firmware, let's do the right thing.

> +
> +	val = readl_relaxed(tsc_base + TSC_CNTCR);
> +	val |= TSC_CNTCR_ENABLE | TSC_CNTCR_HDBG;
> +	writel_relaxed(val, tsc_base + TSC_CNTCR);
> +
> +	err = arch_timer_of_register();

What about adding an optional property to the binding, pointing to the
required clock? That would solve the above problem in a sensible way,
and your kernel wouldn't go bust.

	M.
-- 
Jazz is not dead. It just smells funny...