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Date:	Thu, 20 Dec 2012 13:33:38 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Hiroshi Doyu <hdoyu@...dia.com>
CC:	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"andrew@...n.ch" <andrew@...n.ch>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"jason@...edaemon.net" <jason@...edaemon.net>,
	"johnstul@...ibm.com" <johnstul@...ibm.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 5/9] clocksource: tegra: Enable ARM arch_timer with TSC

On 20/12/12 13:25, Hiroshi Doyu wrote:
> Marc Zyngier <marc.zyngier@....com> wrote @ Thu, 20 Dec 2012 13:05:45 +0100:
> 
>> On 20/12/12 11:57, Hiroshi Doyu wrote:
>>> Marc Zyngier <marc.zyngier@....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@...dia.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)?

All platforms are currently doing it in their firmware/bootloader, which
runs on the secure side. The kernel itself should be able to run on both
sides.

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

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