Re: [PATCH v5 3/6] arm64: arch_timer: Work around Erratum Hisilicon-161601

[Kefeng Wang <wangkefeng.wang-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]

On 2016/12/23 15:04, Ding Tianhong wrote:
> Erratum Hisilicon-161601 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.
> 
> The workaround is enabled if the hisilicon,erratum-161601 property is found in
> the timer node in the device tree. This can be overridden with the
> clocksource.arm_arch_timer.hisilicon-161601 boot parameter, which allows KVM
> users to enable the workaround until a mechanism is implemented to
> automatically communicate this information.
> 
> Fix some description for fsl erratum a008585.
> 
> v2: Significant rework based on feedback, including seperate the fsl erratum a008585
>     to another patch, update the erratum name and remove unwanted code.
> 
> v3: Significant rework based on feedback, including fix some alignment problem, make the
>     #define __hisi_161601_read_reg to be private to the .c file instead of being globally
>     visible, add more accurate annotation and modify a bit of logical format to enable
>     arch_timer_read_ool_enabled, remove the kernel commandline parameter
>     clocksource.arm_arch_timer.hisilicon-161601.
> 
> v5: 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 to 50 which is far
>     beyond the number of iterations the loop has been observed to take.
> 
> Signed-off-by: Ding Tianhong <dingtianhong-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
> ---
>  Documentation/arm64/silicon-errata.txt |  1 +
>  arch/arm64/include/asm/arch_timer.h    |  2 +-
>  drivers/clocksource/Kconfig            |  9 +++++
>  drivers/clocksource/arm_arch_timer.c   | 70 +++++++++++++++++++++++++++++++---
>  4 files changed, 76 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt
> index 405da11..1c1a95f 100644
> --- a/Documentation/arm64/silicon-errata.txt
> +++ b/Documentation/arm64/silicon-errata.txt
> @@ -63,3 +63,4 @@ stable kernels.
>  | Cavium         | ThunderX SMMUv2 | #27704          | N/A		       |
>  |                |                 |                 |                         |
>  | Freescale/NXP  | LS2080A/LS1043A | A-008585        | FSL_ERRATUM_A008585     |
> +| Hisilicon      | Hip0{5,6,7}     | #161601         | HISILICON_ERRATUM_161601|
> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
> index f882c7c..ebf4cde 100644
> --- a/arch/arm64/include/asm/arch_timer.h
> +++ b/arch/arm64/include/asm/arch_timer.h
> @@ -29,7 +29,7 @@
>  
>  #include <clocksource/arm_arch_timer.h>
>  
> -#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585)
> +#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
>  extern struct static_key_false arch_timer_read_ool_enabled;
>  #define needs_unstable_timer_counter_workaround() \
>  	static_branch_unlikely(&arch_timer_read_ool_enabled)
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index 4866f7a..162d820 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -335,6 +335,15 @@ 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_161601
> +	bool "Workaround for Hisilicon Erratum 161601"
> +	default y
> +	depends on ARM_ARCH_TIMER && ARM64
> +	help
> +	  This option enables a workaround for Hisilicon Erratum
> +	  161601. The workaround will be active if the hisilicon,erratum-161601
> +	  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 e7406ad..9a82496 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -95,15 +95,18 @@ static int __init early_evtstrm_cfg(char *buf)
>   * Architected system timer support.
>   */
>  
> -#ifdef CONFIG_FSL_ERRATUM_A008585
> +#if CONFIG_FSL_ERRATUM_A008585 || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
>  struct arch_timer_erratum_workaround *timer_unstable_counter_workaround = NULL;
>  EXPORT_SYMBOL_GPL(timer_unstable_counter_workaround);
>  


>  #define        FSL_A008585	0x0001
> +#define        HISILICON_161601	0x0002

It looks like the DEFINE is useless，

> +
> +static struct arch_timer_erratum_workaround arch_timer_hisi_161601 = {
> +	.erratum = HISILICON_161601,

Just a errata description, eg.
	.desc	= "HISILICON ERRATUM 161601"
then....

> +	.read_cntp_tval_el0 = hisi_161601_read_cntp_tval_el0,
> +	.read_cntv_tval_el0 = hisi_161601_read_cntv_tval_el0,
> +	.read_cntvct_el0 = hisi_161601_read_cntvct_el0,
> +};
> +#endif /* CONFIG_HISILICON_ERRATUM_161601 */
[..]

> -#ifdef CONFIG_FSL_ERRATUM_A008585
> +#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
>  		/*
>  		 * Don't use the vdso fastpath if errata require using
>  		 * the out-of-line counter accessor.
> @@ -909,10 +960,19 @@ static int __init arch_timer_of_init(struct device_node *np)
>  #ifdef CONFIG_FSL_ERRATUM_A008585
>  	if (!timer_unstable_counter_workaround && of_property_read_bool(np, "fsl,erratum-a008585"))
>  		timer_unstable_counter_workaround = &arch_timer_fsl_a008585;
> +#endif
> +
> +#ifdef CONFIG_HISILICON_ERRATUM_161601
> +	if (!timer_unstable_counter_workaround && of_property_read_bool(np, "hisilicon,erratum-161601"))
> +		timer_unstable_counter_workaround = &arch_timer_hisi_161601;
> +#endif
>  
> +#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
>  	if (timer_unstable_counter_workaround) {
>  		static_branch_enable(&arch_timer_read_ool_enabled);
> -		pr_info("Enabling workaround for FSL erratum A-008585\n");
> +		pr_info("Enabling workaround for %s\n",
> +			timer_unstable_counter_workaround->erratum == FSL_A008585 ?
> +			"FSL ERRATUM A-008585" : "HISILICON ERRATUM 161601");

......>		pr_info("Enabling workaround for %s\n", timer_unstable_counter_workaround->desc)

>  	}
>  #endif
>  
> 

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