Re: [PATCH 5/7] arm64: arch_timer: work around Hisilicon erratum 161010101

[Mark Rutland]

Hi Daniel,

On Tue, Jan 31, 2017 at 12:19:54PM +0000, Mark Rutland wrote:
> From: Ding Tianhong <dingtianhong@xxxxxxxxxx>
> 
> Erratum Hisilicon-161010101 says that the ARM generic timer counter "has
> the potential to contain an erroneous value when the timer value
> changes". Accesses to TVAL (both read and write) are also affected due
> to the implicit counter read. Accesses to CVAL are not affected.
> 
> The workaround is to reread the system count registers until the value
> of the second read is larger than the first one by less than 32, the
> system counter can be guaranteed not to return wrong value twice by
> back-to-back read and the error value is always larger than the correct
> one by 32. Writes to TVAL are replaced with an equivalent write to CVAL.
> 
> Signed-off-by: Ding Tianhong <dingtianhong@xxxxxxxxxx>
> [Mark: split patch, fix Kconfig, reword commit message]
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> ---
>  drivers/clocksource/Kconfig          | 10 ++++++++
>  drivers/clocksource/arm_arch_timer.c | 49 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 59 insertions(+)

Do you have any comments on this patch?

What would you prefer to do w.r.t. taking these patches? Would you like
me to resend the clocksource patches in isolation, or as a pull?

Thanks,
Mark.

> 
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index e132bb3..17ee71c 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -339,6 +339,16 @@ config FSL_ERRATUM_A008585
>  	  value").  The workaround will only be active if the
>  	  fsl,erratum-a008585 property is found in the timer node.
>  
> +config HISILICON_ERRATUM_161010101
> +	bool "Workaround for Hisilicon Erratum 161010101"
> +	default y
> +	select ARM_ARCH_TIMER_OOL_WORKAROUND
> +	depends on ARM_ARCH_TIMER && ARM64
> +	help
> +	  This option enables a workaround for Hisilicon Erratum
> +	  161010101. The workaround will be active if the hisilicon,erratum-161010101
> +	  property is found in the timer node.
> +
>  config ARM_GLOBAL_TIMER
>  	bool "Support for the ARM global timer" if COMPILE_TEST
>  	select CLKSRC_OF if OF
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 2af0739..7b06aef 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -130,6 +130,47 @@ static u64 notrace fsl_a008585_read_cntvct_el0(void)
>  }
>  #endif
>  
> +#ifdef CONFIG_HISILICON_ERRATUM_161010101
> +/*
> + * Verify whether the value of the second read is larger than the first by
> + * less than 32 is the only way to confirm the value is correct, so clear the
> + * lower 5 bits to check whether the difference is greater than 32 or not.
> + * Theoretically the erratum should not occur more than twice in succession
> + * when reading the system counter, but it is possible that some interrupts
> + * may lead to more than twice read errors, triggering the warning, so setting
> + * the number of retries far beyond the number of iterations the loop has been
> + * observed to take.
> + */
> +#define __hisi_161010101_read_reg(reg) ({				\
> +	u64 _old, _new;						\
> +	int _retries = 50;					\
> +								\
> +	do {							\
> +		_old = read_sysreg(reg);			\
> +		_new = read_sysreg(reg);			\
> +		_retries--;					\
> +	} while (unlikely((_new - _old) >> 5) && _retries);	\
> +								\
> +	WARN_ON_ONCE(!_retries);				\
> +	_new;							\
> +})
> +
> +static u32 notrace hisi_161010101_read_cntp_tval_el0(void)
> +{
> +	return __hisi_161010101_read_reg(cntp_tval_el0);
> +}
> +
> +static u32 notrace hisi_161010101_read_cntv_tval_el0(void)
> +{
> +	return __hisi_161010101_read_reg(cntv_tval_el0);
> +}
> +
> +static u64 notrace hisi_161010101_read_cntvct_el0(void)
> +{
> +	return __hisi_161010101_read_reg(cntvct_el0);
> +}
> +#endif
> +
>  #ifdef CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND
>  const struct arch_timer_erratum_workaround *timer_unstable_counter_workaround = NULL;
>  EXPORT_SYMBOL_GPL(timer_unstable_counter_workaround);
> @@ -146,6 +187,14 @@ static u64 notrace fsl_a008585_read_cntvct_el0(void)
>  		.read_cntvct_el0 = fsl_a008585_read_cntvct_el0,
>  	},
>  #endif
> +#ifdef CONFIG_HISILICON_ERRATUM_161010101
> +	{
> +		.id = "hisilicon,erratum-161010101",
> +		.read_cntp_tval_el0 = hisi_161010101_read_cntp_tval_el0,
> +		.read_cntv_tval_el0 = hisi_161010101_read_cntv_tval_el0,
> +		.read_cntvct_el0 = hisi_161010101_read_cntvct_el0,
> +	},
> +#endif
>  };
>  #endif /* CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND */
>  
> -- 
> 1.9.1
>