linux-kernel - Re: [PATCH v4] clocksource: arch_timer: Fix code to use physical timers when requested

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Message-ID: <546DC089.9020507@linaro.org>
Date:	Thu, 20 Nov 2014 11:20:57 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Sonny Rao <sonnyrao@...omium.org>,
	linux-arm-kernel@...ts.infradead.org
CC:	linux-kernel@...r.kernel.org, dianders@...omium.org,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>,
	Olof Johansson <olof@...om.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Russell King <linux@....linux.org.uk>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Mark Rutland <Mark.Rutland@....com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Marc Zyngier <marc.zyngier@....com>, stable@...r.kernel.org
Subject: Re: [PATCH v4] clocksource: arch_timer: Fix code to use physical
 timers when requested

On 10/08/2014 09:38 AM, Sonny Rao wrote:
> This is a bug fix for using physical arch timers when
> the arch_timer_use_virtual boolean is false.  It restores the
> arch_counter_get_cntpct() function after removal in
>
> 0d651e4e "clocksource: arch_timer: use virtual counters"
>
> We need this on certain ARMv7 systems which are architected like this:
>
> * The firmware doesn't know and doesn't care about hypervisor mode and
>    we don't want to add the complexity of hypervisor there.
>
> * The firmware isn't involved in SMP bringup or resume.
>
> * The ARCH timer come up with an uninitialized offset between the
>    virtual and physical counters.  Each core gets a different random
>    offset.
>
> * The device boots in "Secure SVC" mode.
>
> * Nothing has touched the reset value of CNTHCTL.PL1PCEN or
>    CNTHCTL.PL1PCTEN (both default to 1 at reset)
>
> One example of such as system is RK3288 where it is much simpler to
> use the physical counter since there's nobody managing the offset and
> each time a core goes down and comes back up it will get reinitialized
> to some other random value.
>
> Fixes: 0d651e4e65e9 ("clocksource: arch_timer: use virtual counters")
> Cc: stable@...r.kernel.org
> Signed-off-by: Sonny Rao <sonnyrao@...omium.org>
> Acked-by: Olof Johansson <olof@...om.net>
> ---

Hi Sonny,

the patch does not apply. Could you refresh it please ?

Thanks
   -- Daniel

> v2: Add fixes tag to commit message, cc stable, copy Doug's
>      description of the systems which need this in commit message.
> v3: Don't change the memory-mapped physical timer/counter code
> v4: remove the memory-mapped physical counter code since it's not used
> ---
>   arch/arm/include/asm/arch_timer.h    |  9 +++++++++
>   arch/arm64/include/asm/arch_timer.h  | 10 ++++++++++
>   drivers/clocksource/arm_arch_timer.c | 10 +++++++---
>   3 files changed, 26 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
> index 0704e0c..e72aa4d 100644
> --- a/arch/arm/include/asm/arch_timer.h
> +++ b/arch/arm/include/asm/arch_timer.h
> @@ -78,6 +78,15 @@ static inline u32 arch_timer_get_cntfrq(void)
>   	return val;
>   }
>
> +static inline u64 arch_counter_get_cntpct(void)
> +{
> +	u64 cval;
> +
> +	isb();
> +	asm volatile("mrrc p15, 0, %Q0, %R0, c14" : "=r" (cval));
> +	return cval;
> +}
> +
>   static inline u64 arch_counter_get_cntvct(void)
>   {
>   	u64 cval;
> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
> index 9400596..58657c4 100644
> --- a/arch/arm64/include/asm/arch_timer.h
> +++ b/arch/arm64/include/asm/arch_timer.h
> @@ -135,6 +135,16 @@ static inline void arch_timer_evtstrm_enable(int divider)
>   #endif
>   }
>
> +static inline u64 arch_counter_get_cntpct(void)
> +{
> +	u64 cval;
> +
> +	isb();
> +	asm volatile("mrs %0, cntpct_el0" : "=r" (cval));
> +
> +	return cval;
> +}
> +
>   static inline u64 arch_counter_get_cntvct(void)
>   {
>   	u64 cval;
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 6b50311..799139f 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -429,10 +429,14 @@ static void __init arch_counter_register(unsigned type)
>   	u64 start_count;
>
>   	/* Register the CP15 based counter if we have one */
> -	if (type & ARCH_CP15_TIMER)
> -		arch_timer_read_counter = arch_counter_get_cntvct;
> -	else
> +	if (type & ARCH_CP15_TIMER) {
> +		if (arch_timer_use_virtual)
> +			arch_timer_read_counter = arch_counter_get_cntvct;
> +		else
> +			arch_timer_read_counter = arch_counter_get_cntpct;
> +	} else {
>   		arch_timer_read_counter = arch_counter_get_cntvct_mem;
> +	}
>
>   	start_count = arch_timer_read_counter();
>   	clocksource_register_hz(&clocksource_counter, arch_timer_rate);
>


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