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Message-ID: <50D313B2.8050805@arm.com>
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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