[PATCH v3 1/2] arm_arch_timer: Expose event stream status

[julien.thierry@arm.com (Julien Thierry)]

Hi Will,

On 11/10/17 16:14, Will Deacon wrote:
> Hi Julien,
> 
> On Fri, Sep 29, 2017 at 11:52:29AM +0100, Julien Thierry wrote:
>> The arch timer configuration for a CPU might get reset after suspending
>> said CPU.
>>
>> In order to reliably use the event stream in the kernel (e.g. for delays),
>> we keep track of the state where we can safely concider the event stream as
>> properly configured.
>>
>> Signed-off-by: Julien Thierry <julien.thierry@arm.com>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Cc: Marc Zyngier <marc.zyngier@arm.com>
>> Cc: Russell King <linux@armlinux.org.uk>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will.deacon@arm.com>
>> ---
>>   arch/arm/include/asm/arch_timer.h    |  1 +
>>   arch/arm64/include/asm/arch_timer.h  |  1 +
>>   drivers/clocksource/arm_arch_timer.c | 20 ++++++++++++++++++--
>>   include/clocksource/arm_arch_timer.h |  6 ++++++
>>   4 files changed, 26 insertions(+), 2 deletions(-)
> 
> The arch-timer bits needs an ack from Marc or Mark.
> 
>> diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
>> index d4ebf56..0b6e104 100644
>> --- a/arch/arm/include/asm/arch_timer.h
>> +++ b/arch/arm/include/asm/arch_timer.h
>> @@ -106,6 +106,7 @@ static inline u32 arch_timer_get_cntkctl(void)
>>   static inline void arch_timer_set_cntkctl(u32 cntkctl)
>>   {
>>   	asm volatile("mcr p15, 0, %0, c14, c1, 0" : : "r" (cntkctl));
>> +	isb();
>>   }
>>
>>   #endif
>> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
>> index a652ce0..bdedd8f 100644
>> --- a/arch/arm64/include/asm/arch_timer.h
>> +++ b/arch/arm64/include/asm/arch_timer.h
>> @@ -144,6 +144,7 @@ static inline u32 arch_timer_get_cntkctl(void)
>>   static inline void arch_timer_set_cntkctl(u32 cntkctl)
>>   {
>>   	write_sysreg(cntkctl, cntkctl_el1);
>> +	isb();
>>   }
>>
>>   static inline u64 arch_counter_get_cntpct(void)
>> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
>> index fd4b7f6..47cf15e 100644
>> --- a/drivers/clocksource/arm_arch_timer.c
>> +++ b/drivers/clocksource/arm_arch_timer.c
>> @@ -77,6 +77,7 @@ struct arch_timer {
>>   static bool arch_counter_suspend_stop;
>>   static bool vdso_default = true;
>>
>> +static cpumask_t evtstrm_available;
>>   static bool evtstrm_enable = IS_ENABLED(CONFIG_ARM_ARCH_TIMER_EVTSTREAM);
>>
>>   static int __init early_evtstrm_cfg(char *buf)
>> @@ -740,6 +741,7 @@ static void arch_timer_evtstrm_enable(int divider)
>>   #ifdef CONFIG_COMPAT
>>   	compat_elf_hwcap |= COMPAT_HWCAP_EVTSTRM;
>>   #endif
>> +	cpumask_set_cpu(smp_processor_id(), &evtstrm_available);
>>   }
>>
>>   static void arch_timer_configure_evtstream(void)
>> @@ -864,6 +866,11 @@ u32 arch_timer_get_rate(void)
>>   	return arch_timer_rate;
>>   }
>>
>> +bool arch_timer_evtstrm_available(void)
>> +{
>> +	return !!cpumask_test_cpu(smp_processor_id(), &evtstrm_available);
>> +}
> 
> I don't think you need the '!!' prefix here.

True, I'll remove that.

> 
>> +
>>   static u64 arch_counter_get_cntvct_mem(void)
>>   {
>>   	u32 vct_lo, vct_hi, tmp_hi;
>> @@ -929,6 +936,8 @@ static int arch_timer_dying_cpu(unsigned int cpu)
>>   {
>>   	struct clock_event_device *clk = this_cpu_ptr(arch_timer_evt);
>>
>> +	cpumask_clear_cpu(smp_processor_id(), &evtstrm_available);
>> +
>>   	arch_timer_stop(clk);
>>   	return 0;
>>   }
>> @@ -938,10 +947,16 @@ static int arch_timer_dying_cpu(unsigned int cpu)
>>   static int arch_timer_cpu_pm_notify(struct notifier_block *self,
>>   				    unsigned long action, void *hcpu)
>>   {
>> -	if (action == CPU_PM_ENTER)
>> +	if (action == CPU_PM_ENTER) {
>>   		__this_cpu_write(saved_cntkctl, arch_timer_get_cntkctl());
>> -	else if (action == CPU_PM_ENTER_FAILED || action == CPU_PM_EXIT)
>> +
>> +		cpumask_clear_cpu(smp_processor_id(), &evtstrm_available);
>> +	} else if (action == CPU_PM_ENTER_FAILED || action == CPU_PM_EXIT) {
>>   		arch_timer_set_cntkctl(__this_cpu_read(saved_cntkctl));
>> +
>> +		if (elf_hwcap & HWCAP_EVTSTRM)
>> +			cpumask_set_cpu(smp_processor_id(), &evtstrm_available);
>> +	}
>>   	return NOTIFY_OK;
>>   }
>>
>> @@ -1017,6 +1032,7 @@ static int __init arch_timer_register(void)
>>   	if (err)
>>   		goto out_unreg_notify;
>>
>> +	cpumask_clear(&evtstrm_available);
> 
> This should already be ok by virtue of the mask being static, no?
> Alternatively, you could use the CPU_MASK_NONE static initialiser.

Yes, I just prefer explicit initialisations. But you're right, I'll use 
CPU_MASK_NONE unless it is encouraged to rely on implicit intilisation.

Thanks,

-- 
Julien Thierry