[PATCH v5] clocksource: arch_timer: Fix code to use physical timers when requested

[Daniel Lezcano]

On 11/24/2014 08:02 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 at vger.kernel.org
> Signed-off-by: Sonny Rao <sonnyrao at chromium.org>
> Acked-by: Olof Johansson <olof at lixom.net>

Acked-by: Daniel Lezcano <daniel.lezcano at linaro.org>



> ---
> 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
> v5: rebase and make AArch64 version of arch_counter_get_cntpct call BUG()
> ---
>   arch/arm/include/asm/arch_timer.h    | 9 +++++++++
>   arch/arm64/include/asm/arch_timer.h  | 9 +++++++++
>   drivers/clocksource/arm_arch_timer.c | 5 ++++-
>   3 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
> index 92793ba..d4ebf56 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 f190971..b1fa4e6 100644
> --- a/arch/arm64/include/asm/arch_timer.h
> +++ b/arch/arm64/include/asm/arch_timer.h
> @@ -104,6 +104,15 @@ static inline void arch_timer_set_cntkctl(u32 cntkctl)
>   	asm volatile("msr	cntkctl_el1, %0" : : "r" (cntkctl));
>   }
>
> +static inline u64 arch_counter_get_cntpct(void)
> +{
> +	/*
> +	 * AArch64 kernel and user space mandate the use of CNTVCT.
> +	 */
> +	BUG();
> +	return 0;
> +}
> +
>   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 43005d4..1fa2af9 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -462,7 +462,10 @@ static void __init arch_counter_register(unsigned type)
>
>   	/* Register the CP15 based counter if we have one */
>   	if (type & ARCH_CP15_TIMER) {
> -		arch_timer_read_counter = arch_counter_get_cntvct;
> +		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;
>
>


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