[PATCH v2 1/4] arm64: arch_timer: Add device tree binding for hisilicon-161601 erratum

[PATCH v2 1/4] arm64: arch_timer: Add device tree binding for hisilicon-161601 erratum

[Ding Tianhong]

This erratum describes a bug in logic outside the core, so MIDR can't be
used to identify its presence, and reading an SoC-specific revision
register from common arch timer code would be awkward.  So, describe it
in the device tree.

v2: Use the new erratum name and update the description.

Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
---
 Documentation/devicetree/bindings/arm/arch_timer.txt | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/devicetree/bindings/arm/arch_timer.txt b/Documentation/devicetree/bindings/arm/arch_timer.txt
index ef5fbe9..c27b2c4 100644
--- a/Documentation/devicetree/bindings/arm/arch_timer.txt
+++ b/Documentation/devicetree/bindings/arm/arch_timer.txt
@@ -31,6 +31,14 @@ to deliver its interrupts via SPIs.
   This also affects writes to the tval register, due to the implicit
   counter read.
 
+- hisilicon,erratum-161601 : A boolean property. Indicates the presence of
+  erratum 161601, which says that reading the counter is unreliable unless
+  reading twice on the register and the value of the second read is larger
+  than the first by less than 32. If the verification is unsuccessful, then
+  discard the value of this read and repeat this procedure until the verification
+  is successful.  This also affects writes to the tval register, due to the
+  implicit counter read.
+
 ** Optional properties:
 
 - arm,cpu-registers-not-fw-configured : Firmware does not initialize
-- 
1.9.0

[PATCH v2 2/4] arm64: arch_timer: Introduce a generic erratum handing mechanism for fsl-a008585

[Ding Tianhong]

The workaround for hisilicon,161601 will check the return value of the system counter
by different way, in order to distinguish with the fsl-a008585 workaround, introduce
a new generic erratum handing mechanism for fsl-a008585 and rename some functions. 

v2: Introducing a new generic erratum handling mechanism for fsl erratum a008585.

Signed-off-by: Ding Tianhong <dingtianhong-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
---
 arch/arm64/include/asm/arch_timer.h  | 20 +++++++++-----
 drivers/clocksource/arm_arch_timer.c | 51 +++++++++++++++++++++---------------
 2 files changed, 43 insertions(+), 28 deletions(-)

diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index eaa5bbe..118719d8 100644
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h
@@ -31,15 +31,21 @@
 
 #if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585)
 extern struct static_key_false arch_timer_read_ool_enabled;
-#define needs_fsl_a008585_workaround() \
+#define needs_timer_erratum_workaround() \
 	static_branch_unlikely(&arch_timer_read_ool_enabled)
 #else
-#define needs_fsl_a008585_workaround()  false
+#define needs_timer_erratum_workaround()  false
 #endif
 
-u32 __fsl_a008585_read_cntp_tval_el0(void);
-u32 __fsl_a008585_read_cntv_tval_el0(void);
-u64 __fsl_a008585_read_cntvct_el0(void);
+
+struct arch_timer_erratum_workaround {
+	int erratum;
+	u32 (*read_cntp_tval_el0)(void);
+	u32 (*read_cntv_tval_el0)(void);
+	u64 (*read_cntvct_el0)(void);
+};
+
+extern struct arch_timer_erratum_workaround *erratum_workaround;
 
 /*
  * The number of retries is an arbitrary value well beyond the highest number
@@ -62,8 +68,8 @@ u64 __fsl_a008585_read_cntvct_el0(void);
 #define arch_timer_reg_read_stable(reg) 		\
 ({							\
 	u64 _val;					\
-	if (needs_fsl_a008585_workaround())		\
-		_val = __fsl_a008585_read_##reg();	\
+	if (needs_timer_erratum_workaround())		\
+		_val = erratum_workaround->read_##reg();	\
 	else						\
 		_val = read_sysreg(reg);		\
 	_val;						\
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 73c487d..e4f7fa1 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -95,10 +95,32 @@ early_param("clocksource.arm_arch_timer.evtstrm", early_evtstrm_cfg);
  */
 
 #ifdef CONFIG_FSL_ERRATUM_A008585
+struct arch_timer_erratum_workaround *erratum_workaround = NULL;
+
 DEFINE_STATIC_KEY_FALSE(arch_timer_read_ool_enabled);
 EXPORT_SYMBOL_GPL(arch_timer_read_ool_enabled);
 
-static int fsl_a008585_enable = -1;
+
+static u32 fsl_a008585_read_cntp_tval_el0(void)
+{
+	return __fsl_a008585_read_reg(cntp_tval_el0);
+}
+
+static  u32 fsl_a008585_read_cntv_tval_el0(void)
+{
+	return __fsl_a008585_read_reg(cntv_tval_el0);
+}
+
+static u64 fsl_a008585_read_cntvct_el0(void)
+{
+	return __fsl_a008585_read_reg(cntvct_el0);
+}
+
+static struct arch_timer_erratum_workaround arch_timer_fsl_a008585 = {
+	.read_cntp_tval_el0 = fsl_a008585_read_cntp_tval_el0,
+	.read_cntv_tval_el0 = fsl_a008585_read_cntv_tval_el0,
+	.read_cntvct_el0 = fsl_a008585_read_cntvct_el0,
+};
 
 static int __init early_fsl_a008585_cfg(char *buf)
 {
@@ -109,26 +131,12 @@ static int __init early_fsl_a008585_cfg(char *buf)
 	if (ret)
 		return ret;
 
-	fsl_a008585_enable = val;
+	if (val)
+		erratum_workaround = &arch_timer_fsl_a008585;
+
 	return 0;
 }
 early_param("clocksource.arm_arch_timer.fsl-a008585", early_fsl_a008585_cfg);
-
-u32 __fsl_a008585_read_cntp_tval_el0(void)
-{
-	return __fsl_a008585_read_reg(cntp_tval_el0);
-}
-
-u32 __fsl_a008585_read_cntv_tval_el0(void)
-{
-	return __fsl_a008585_read_reg(cntv_tval_el0);
-}
-
-u64 __fsl_a008585_read_cntvct_el0(void)
-{
-	return __fsl_a008585_read_reg(cntvct_el0);
-}
-EXPORT_SYMBOL(__fsl_a008585_read_cntvct_el0);
 #endif /* CONFIG_FSL_ERRATUM_A008585 */
 
 static __always_inline
@@ -891,9 +899,10 @@ static int __init arch_timer_of_init(struct device_node *np)
 	arch_timer_c3stop = !of_property_read_bool(np, "always-on");
 
 #ifdef CONFIG_FSL_ERRATUM_A008585
-	if (fsl_a008585_enable < 0)
-		fsl_a008585_enable = of_property_read_bool(np, "fsl,erratum-a008585");
-	if (fsl_a008585_enable) {
+	if (!erratum_workaround && of_property_read_bool(np, "fsl,erratum-a008585"))
+		erratum_workaround = &arch_timer_fsl_a008585;
+
+	if (erratum_workaround) {
 		static_branch_enable(&arch_timer_read_ool_enabled);
 		pr_info("Enabling workaround for FSL erratum A-008585\n");
 	}
-- 
1.9.0


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Re: [PATCH v2 2/4] arm64: arch_timer: Introduce a generic erratum handing mechanism for fsl-a008585

[Marc Zyngier]

On 27/10/16 08:34, Ding Tianhong wrote:
> The workaround for hisilicon,161601 will check the return value of the system counter
> by different way, in order to distinguish with the fsl-a008585 workaround, introduce
> a new generic erratum handing mechanism for fsl-a008585 and rename some functions. 
> 
> v2: Introducing a new generic erratum handling mechanism for fsl erratum a008585.
> 
> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
> ---
>  arch/arm64/include/asm/arch_timer.h  | 20 +++++++++-----
>  drivers/clocksource/arm_arch_timer.c | 51 +++++++++++++++++++++---------------
>  2 files changed, 43 insertions(+), 28 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
> index eaa5bbe..118719d8 100644
> --- a/arch/arm64/include/asm/arch_timer.h
> +++ b/arch/arm64/include/asm/arch_timer.h
> @@ -31,15 +31,21 @@
>  
>  #if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585)
>  extern struct static_key_false arch_timer_read_ool_enabled;
> -#define needs_fsl_a008585_workaround() \
> +#define needs_timer_erratum_workaround() \
>  	static_branch_unlikely(&arch_timer_read_ool_enabled)

This is too generic a name. Please make it more specific.

>  #else
> -#define needs_fsl_a008585_workaround()  false
> +#define needs_timer_erratum_workaround()  false
>  #endif
>  
> -u32 __fsl_a008585_read_cntp_tval_el0(void);
> -u32 __fsl_a008585_read_cntv_tval_el0(void);
> -u64 __fsl_a008585_read_cntvct_el0(void);
> +
> +struct arch_timer_erratum_workaround {
> +	int erratum;

What is the use of this field?

> +	u32 (*read_cntp_tval_el0)(void);
> +	u32 (*read_cntv_tval_el0)(void);
> +	u64 (*read_cntvct_el0)(void);
> +};
> +
> +extern struct arch_timer_erratum_workaround *erratum_workaround;

This is a very generic name for something that has a global visibility.
Please choose a more specific variable name.

>  
>  /*
>   * The number of retries is an arbitrary value well beyond the highest number
> @@ -62,8 +68,8 @@ u64 __fsl_a008585_read_cntvct_el0(void);
>  #define arch_timer_reg_read_stable(reg) 		\
>  ({							\
>  	u64 _val;					\
> -	if (needs_fsl_a008585_workaround())		\
> -		_val = __fsl_a008585_read_##reg();	\
> +	if (needs_timer_erratum_workaround())		\
> +		_val = erratum_workaround->read_##reg();	\

As mentioned in my initial review, you've now broken modular access to
any of the registers. Please fix it.

>  	else						\
>  		_val = read_sysreg(reg);		\
>  	_val;						\
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 73c487d..e4f7fa1 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -95,10 +95,32 @@ early_param("clocksource.arm_arch_timer.evtstrm", early_evtstrm_cfg);
>   */
>  
>  #ifdef CONFIG_FSL_ERRATUM_A008585
> +struct arch_timer_erratum_workaround *erratum_workaround = NULL;
> +
>  DEFINE_STATIC_KEY_FALSE(arch_timer_read_ool_enabled);
>  EXPORT_SYMBOL_GPL(arch_timer_read_ool_enabled);
>  
> -static int fsl_a008585_enable = -1;
> +
> +static u32 fsl_a008585_read_cntp_tval_el0(void)
> +{
> +	return __fsl_a008585_read_reg(cntp_tval_el0);
> +}
> +
> +static  u32 fsl_a008585_read_cntv_tval_el0(void)
> +{
> +	return __fsl_a008585_read_reg(cntv_tval_el0);
> +}
> +
> +static u64 fsl_a008585_read_cntvct_el0(void)
> +{
> +	return __fsl_a008585_read_reg(cntvct_el0);
> +}

So now that you've indirected all calls through a set of pointers, why
do you keep the __fsl_a008585_read_reg() macro inside the include file?
I don't think it has any purpose in being globally visible now.

> +
> +static struct arch_timer_erratum_workaround arch_timer_fsl_a008585 = {

And here's the proof that the erratum field is useless.

> +	.read_cntp_tval_el0 = fsl_a008585_read_cntp_tval_el0,
> +	.read_cntv_tval_el0 = fsl_a008585_read_cntv_tval_el0,
> +	.read_cntvct_el0 = fsl_a008585_read_cntvct_el0,
> +};
>  
>  static int __init early_fsl_a008585_cfg(char *buf)
>  {
> @@ -109,26 +131,12 @@ static int __init early_fsl_a008585_cfg(char *buf)
>  	if (ret)
>  		return ret;
>  
> -	fsl_a008585_enable = val;
> +	if (val)
> +		erratum_workaround = &arch_timer_fsl_a008585;
> +
>  	return 0;
>  }
>  early_param("clocksource.arm_arch_timer.fsl-a008585", early_fsl_a008585_cfg);
> -
> -u32 __fsl_a008585_read_cntp_tval_el0(void)
> -{
> -	return __fsl_a008585_read_reg(cntp_tval_el0);
> -}
> -
> -u32 __fsl_a008585_read_cntv_tval_el0(void)
> -{
> -	return __fsl_a008585_read_reg(cntv_tval_el0);
> -}
> -
> -u64 __fsl_a008585_read_cntvct_el0(void)
> -{
> -	return __fsl_a008585_read_reg(cntvct_el0);
> -}
> -EXPORT_SYMBOL(__fsl_a008585_read_cntvct_el0);
>  #endif /* CONFIG_FSL_ERRATUM_A008585 */
>  
>  static __always_inline
> @@ -891,9 +899,10 @@ static int __init arch_timer_of_init(struct device_node *np)
>  	arch_timer_c3stop = !of_property_read_bool(np, "always-on");
>  
>  #ifdef CONFIG_FSL_ERRATUM_A008585
> -	if (fsl_a008585_enable < 0)
> -		fsl_a008585_enable = of_property_read_bool(np, "fsl,erratum-a008585");
> -	if (fsl_a008585_enable) {
> +	if (!erratum_workaround && of_property_read_bool(np, "fsl,erratum-a008585"))
> +		erratum_workaround = &arch_timer_fsl_a008585;

It used to be possible to disable the erratum workaround on the command
line, and you've just removed that feature. Please restore it.

> +
> +	if (erratum_workaround) {
>  		static_branch_enable(&arch_timer_read_ool_enabled);
>  		pr_info("Enabling workaround for FSL erratum A-008585\n");
>  	}
> 

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

[PATCH v2 3/4] arm64: arch_timer: Work around Erratum Hisilicon-161601

[Ding Tianhong]

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.

Signed-off-by: Ding Tianhong <dingtianhong-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
---
 Documentation/arm64/silicon-errata.txt |  1 +
 Documentation/kernel-parameters.txt    |  9 ++++
 arch/arm64/include/asm/arch_timer.h    | 28 ++++++++++-
 drivers/clocksource/Kconfig            | 14 +++++-
 drivers/clocksource/arm_arch_timer.c   | 88 ++++++++++++++++++++++++++--------
 5 files changed, 118 insertions(+), 22 deletions(-)

diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt
index 405da11..70c5d5e 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      | Hip05/Hip06/Hip07 | #161601       | HISILICON_ERRATUM_161601|
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 6fa1d8a..735b4b6 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -707,6 +707,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			erratum.  If unspecified, the workaround is
 			enabled based on the device tree.
 
+	clocksource.arm_arch_timer.hisilicon-161601=
+			[ARM64]
+			Format: <bool>
+			Enable/disable the workaround of Hisilicon
+			erratum 161601.  This can be useful for KVM
+			guests, if the guest device tree doesn't show the
+			erratum.  If unspecified, the workaround is
+			enabled based on the device tree.
+
 	clearcpuid=BITNUM [X86]
 			Disable CPUID feature X for the kernel. See
 			arch/x86/include/asm/cpufeatures.h for the valid bit
diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index 118719d8..49b3041 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_timer_erratum_workaround() \
 	static_branch_unlikely(&arch_timer_read_ool_enabled)
@@ -65,11 +65,35 @@ extern struct arch_timer_erratum_workaround *erratum_workaround;
 	_new;						\
 })
 
+
+
+/*
+ * The number of retries is an arbitrary value well beyond the highest number
+ * of iterations the loop has been observed to take.
+ * 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, 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.
+ */
+#define __hisi_161601_read_reg(reg) ({				\
+	u64 _old, _new;						\
+	int _retries = 200;					\
+								\
+	do {							\
+		_old = read_sysreg(reg);			\
+		_new = read_sysreg(reg);			\
+		_retries--;					\
+	} while (unlikely((_new - _old) >> 5) && _retries);	\
+								\
+	WARN_ON_ONCE(!_retries);				\
+	_new;							\
+})
+
 #define arch_timer_reg_read_stable(reg) 		\
 ({							\
 	u64 _val;					\
 	if (needs_timer_erratum_workaround())		\
-		_val = erratum_workaround->read_##reg();	\
+		_val = erratum_workaround->read_##reg();\
 	else						\
 		_val = read_sysreg(reg);		\
 	_val;						\
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 8a753fd..4aafb6a 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -312,8 +312,20 @@ config FSL_ERRATUM_A008585
 	help
 	  This option enables a workaround for Freescale/NXP Erratum
 	  A-008585 ("ARM generic timer may contain an erroneous
-	  value").  The workaround will only be active if the
+	  value").  The workaround will be active if the
 	  fsl,erratum-a008585 property is found in the timer node.
+	  This can be overridden with the clocksource.arm_arch_timer.fsl-a008585
+	  boot parameter.
+
+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. This can be overridden with
+	  the clocksource.arm_arch_timer.hisilicon-161601 boot parameter.
 
 config ARM_GLOBAL_TIMER
 	bool "Support for the ARM global timer" if COMPILE_TEST
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index e4f7fa1..89f1895 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -94,13 +94,14 @@ early_param("clocksource.arm_arch_timer.evtstrm", early_evtstrm_cfg);
  * Architected system timer support.
  */
 
-#ifdef CONFIG_FSL_ERRATUM_A008585
+#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
 struct arch_timer_erratum_workaround *erratum_workaround = NULL;
 
 DEFINE_STATIC_KEY_FALSE(arch_timer_read_ool_enabled);
 EXPORT_SYMBOL_GPL(arch_timer_read_ool_enabled);
+#endif
 
-
+#ifdef CONFIG_FSL_ERRATUM_A008585
 static u32 fsl_a008585_read_cntp_tval_el0(void)
 {
 	return __fsl_a008585_read_reg(cntp_tval_el0);
@@ -139,6 +140,45 @@ static int __init early_fsl_a008585_cfg(char *buf)
 early_param("clocksource.arm_arch_timer.fsl-a008585", early_fsl_a008585_cfg);
 #endif /* CONFIG_FSL_ERRATUM_A008585 */
 
+#ifdef CONFIG_HISILICON_ERRATUM_161601
+static u32 hisi_161601_read_cntp_tval_el0(void)
+{
+	return __hisi_161601_read_reg(cntp_tval_el0);
+}
+
+static  u32 hisi_161601_read_cntv_tval_el0(void)
+{
+	return __hisi_161601_read_reg(cntv_tval_el0);
+}
+
+static u64 hisi_161601_read_cntvct_el0(void)
+{
+	return __hisi_161601_read_reg(cntvct_el0);
+}
+
+static struct arch_timer_erratum_workaround arch_timer_hisi_161601 = {
+	.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,
+};
+
+static int __init early_hisi_161601_cfg(char *buf)
+{
+	int ret;
+	bool val;
+
+	ret = strtobool(buf, &val);
+	if (ret)
+		return ret;
+
+	if (val)
+		erratum_workaround = &arch_timer_hisi_161601;
+
+	return 0;
+}
+early_param("clocksource.arm_arch_timer.hisilicon-161601", early_hisi_161601_cfg);
+#endif /* CONFIG_HISILICON_ERRATUM_161601 */
+
 static __always_inline
 void arch_timer_reg_write(int access, enum arch_timer_reg reg, u32 val,
 			  struct clock_event_device *clk)
@@ -288,8 +328,8 @@ static __always_inline void set_next_event(const int access, unsigned long evt,
 	arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, clk);
 }
 
-#ifdef CONFIG_FSL_ERRATUM_A008585
-static __always_inline void fsl_a008585_set_next_event(const int access,
+#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
+static __always_inline void erratum_set_next_event(const int access,
 		unsigned long evt, struct clock_event_device *clk)
 {
 	unsigned long ctrl;
@@ -307,20 +347,20 @@ static __always_inline void fsl_a008585_set_next_event(const int access,
 	arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, clk);
 }
 
-static int fsl_a008585_set_next_event_virt(unsigned long evt,
+static int erratum_set_next_event_virt(unsigned long evt,
 					   struct clock_event_device *clk)
 {
-	fsl_a008585_set_next_event(ARCH_TIMER_VIRT_ACCESS, evt, clk);
+	erratum_set_next_event(ARCH_TIMER_VIRT_ACCESS, evt, clk);
 	return 0;
 }
 
-static int fsl_a008585_set_next_event_phys(unsigned long evt,
+static int erratum_set_next_event_phys(unsigned long evt,
 					   struct clock_event_device *clk)
 {
-	fsl_a008585_set_next_event(ARCH_TIMER_PHYS_ACCESS, evt, clk);
+	erratum_set_next_event(ARCH_TIMER_PHYS_ACCESS, evt, clk);
 	return 0;
 }
-#endif /* CONFIG_FSL_ERRATUM_A008585 */
+#endif
 
 static int arch_timer_set_next_event_virt(unsigned long evt,
 					  struct clock_event_device *clk)
@@ -350,16 +390,16 @@ static int arch_timer_set_next_event_phys_mem(unsigned long evt,
 	return 0;
 }
 
-static void fsl_a008585_set_sne(struct clock_event_device *clk)
+static void erratum_set_sne(struct clock_event_device *clk)
 {
-#ifdef CONFIG_FSL_ERRATUM_A008585
+#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
 	if (!static_branch_unlikely(&arch_timer_read_ool_enabled))
 		return;
 
 	if (arch_timer_uses_ppi == VIRT_PPI)
-		clk->set_next_event = fsl_a008585_set_next_event_virt;
+		clk->set_next_event = erratum_set_next_event_virt;
 	else
-		clk->set_next_event = fsl_a008585_set_next_event_phys;
+		clk->set_next_event = erratum_set_next_event_phys;
 #endif
 }
 
@@ -392,7 +432,7 @@ static void __arch_timer_setup(unsigned type,
 			BUG();
 		}
 
-		fsl_a008585_set_sne(clk);
+		erratum_set_sne(clk);
 	} else {
 		clk->features |= CLOCK_EVT_FEAT_DYNIRQ;
 		clk->name = "arch_mem_timer";
@@ -612,7 +652,7 @@ static void __init arch_counter_register(unsigned type)
 
 		clocksource_counter.archdata.vdso_direct = true;
 
-#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.
@@ -899,12 +939,22 @@ static int __init arch_timer_of_init(struct device_node *np)
 	arch_timer_c3stop = !of_property_read_bool(np, "always-on");
 
 #ifdef CONFIG_FSL_ERRATUM_A008585
-	if (!erratum_workaround && of_property_read_bool(np, "fsl,erratum-a008585"))
+	if (!erratum_workaround && of_property_read_bool(np, "fsl,erratum-a008585")) {
 		erratum_workaround = &arch_timer_fsl_a008585;
+		if (erratum_workaround) {
+			static_branch_enable(&arch_timer_read_ool_enabled);
+			pr_info("Enabling workaround for FSL erratum A-008585\n");
+		}
+	}
+#endif
 
-	if (erratum_workaround) {
-		static_branch_enable(&arch_timer_read_ool_enabled);
-		pr_info("Enabling workaround for FSL erratum A-008585\n");
+#ifdef CONFIG_HISILICON_ERRATUM_161601
+	if (!erratum_workaround && of_property_read_bool(np, "hisilicon,erratum-161601")) {
+		erratum_workaround = &arch_timer_hisi_161601;
+		if (erratum_workaround) {
+			static_branch_enable(&arch_timer_read_ool_enabled);
+			pr_info("Enabling workaround for HISILICON erratum 161601\n");
+		}
 	}
 #endif
 
-- 
1.9.0


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Re: [PATCH v2 3/4] arm64: arch_timer: Work around Erratum Hisilicon-161601

[Marc Zyngier]

On 27/10/16 08:34, 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.
> 
> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
> ---
>  Documentation/arm64/silicon-errata.txt |  1 +
>  Documentation/kernel-parameters.txt    |  9 ++++
>  arch/arm64/include/asm/arch_timer.h    | 28 ++++++++++-
>  drivers/clocksource/Kconfig            | 14 +++++-
>  drivers/clocksource/arm_arch_timer.c   | 88 ++++++++++++++++++++++++++--------
>  5 files changed, 118 insertions(+), 22 deletions(-)
> 
> diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt
> index 405da11..70c5d5e 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      | Hip05/Hip06/Hip07 | #161601       | HISILICON_ERRATUM_161601|

I've already commented on the alignment. Please read my initial review.

> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 6fa1d8a..735b4b6 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -707,6 +707,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  			erratum.  If unspecified, the workaround is
>  			enabled based on the device tree.
>  
> +	clocksource.arm_arch_timer.hisilicon-161601=
> +			[ARM64]
> +			Format: <bool>
> +			Enable/disable the workaround of Hisilicon
> +			erratum 161601.  This can be useful for KVM
> +			guests, if the guest device tree doesn't show the
> +			erratum.  If unspecified, the workaround is
> +			enabled based on the device tree.
> +
>  	clearcpuid=BITNUM [X86]
>  			Disable CPUID feature X for the kernel. See
>  			arch/x86/include/asm/cpufeatures.h for the valid bit
> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
> index 118719d8..49b3041 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_timer_erratum_workaround() \
>  	static_branch_unlikely(&arch_timer_read_ool_enabled)
> @@ -65,11 +65,35 @@ extern struct arch_timer_erratum_workaround *erratum_workaround;
>  	_new;						\
>  })
>  
> +
> +
> +/*
> + * The number of retries is an arbitrary value well beyond the highest number
> + * of iterations the loop has been observed to take.
> + * 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, 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.
> + */
> +#define __hisi_161601_read_reg(reg) ({				\
> +	u64 _old, _new;						\
> +	int _retries = 200;					\

Please document how this value was found (either in the code or in the
commit message).

> +								\
> +	do {							\
> +		_old = read_sysreg(reg);			\
> +		_new = read_sysreg(reg);			\
> +		_retries--;					\
> +	} while (unlikely((_new - _old) >> 5) && _retries);	\
> +								\
> +	WARN_ON_ONCE(!_retries);				\
> +	_new;							\
> +})

Same remark as in the previous patch.

> +
>  #define arch_timer_reg_read_stable(reg) 		\
>  ({							\
>  	u64 _val;					\
>  	if (needs_timer_erratum_workaround())		\
> -		_val = erratum_workaround->read_##reg();	\
> +		_val = erratum_workaround->read_##reg();\
>  	else						\
>  		_val = read_sysreg(reg);		\
>  	_val;						\
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index 8a753fd..4aafb6a 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -312,8 +312,20 @@ config FSL_ERRATUM_A008585
>  	help
>  	  This option enables a workaround for Freescale/NXP Erratum
>  	  A-008585 ("ARM generic timer may contain an erroneous
> -	  value").  The workaround will only be active if the
> +	  value").  The workaround will be active if the
>  	  fsl,erratum-a008585 property is found in the timer node.
> +	  This can be overridden with the clocksource.arm_arch_timer.fsl-a008585
> +	  boot parameter.

Move this hunk to the previous patch.

> +
> +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. This can be overridden with
> +	  the clocksource.arm_arch_timer.hisilicon-161601 boot parameter.
>  
>  config ARM_GLOBAL_TIMER
>  	bool "Support for the ARM global timer" if COMPILE_TEST
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index e4f7fa1..89f1895 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -94,13 +94,14 @@ early_param("clocksource.arm_arch_timer.evtstrm", early_evtstrm_cfg);
>   * Architected system timer support.
>   */
>  
> -#ifdef CONFIG_FSL_ERRATUM_A008585
> +#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
>  struct arch_timer_erratum_workaround *erratum_workaround = NULL;
>  
>  DEFINE_STATIC_KEY_FALSE(arch_timer_read_ool_enabled);
>  EXPORT_SYMBOL_GPL(arch_timer_read_ool_enabled);
> +#endif
>  
> -
> +#ifdef CONFIG_FSL_ERRATUM_A008585
>  static u32 fsl_a008585_read_cntp_tval_el0(void)
>  {
>  	return __fsl_a008585_read_reg(cntp_tval_el0);
> @@ -139,6 +140,45 @@ static int __init early_fsl_a008585_cfg(char *buf)
>  early_param("clocksource.arm_arch_timer.fsl-a008585", early_fsl_a008585_cfg);
>  #endif /* CONFIG_FSL_ERRATUM_A008585 */
>  
> +#ifdef CONFIG_HISILICON_ERRATUM_161601
> +static u32 hisi_161601_read_cntp_tval_el0(void)
> +{
> +	return __hisi_161601_read_reg(cntp_tval_el0);
> +}
> +
> +static  u32 hisi_161601_read_cntv_tval_el0(void)
> +{
> +	return __hisi_161601_read_reg(cntv_tval_el0);
> +}
> +
> +static u64 hisi_161601_read_cntvct_el0(void)
> +{
> +	return __hisi_161601_read_reg(cntvct_el0);
> +}
> +
> +static struct arch_timer_erratum_workaround arch_timer_hisi_161601 = {
> +	.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,
> +};
> +
> +static int __init early_hisi_161601_cfg(char *buf)
> +{
> +	int ret;
> +	bool val;
> +
> +	ret = strtobool(buf, &val);
> +	if (ret)
> +		return ret;
> +
> +	if (val)
> +		erratum_workaround = &arch_timer_hisi_161601;
> +
> +	return 0;
> +}
> +early_param("clocksource.arm_arch_timer.hisilicon-161601", early_hisi_161601_cfg);
> +#endif /* CONFIG_HISILICON_ERRATUM_161601 */
> +
>  static __always_inline
>  void arch_timer_reg_write(int access, enum arch_timer_reg reg, u32 val,
>  			  struct clock_event_device *clk)
> @@ -288,8 +328,8 @@ static __always_inline void set_next_event(const int access, unsigned long evt,
>  	arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, clk);
>  }
>  
> -#ifdef CONFIG_FSL_ERRATUM_A008585
> -static __always_inline void fsl_a008585_set_next_event(const int access,
> +#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
> +static __always_inline void erratum_set_next_event(const int access,
>  		unsigned long evt, struct clock_event_device *clk)
>  {
>  	unsigned long ctrl;
> @@ -307,20 +347,20 @@ static __always_inline void fsl_a008585_set_next_event(const int access,
>  	arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, clk);
>  }
>  
> -static int fsl_a008585_set_next_event_virt(unsigned long evt,
> +static int erratum_set_next_event_virt(unsigned long evt,
>  					   struct clock_event_device *clk)
>  {
> -	fsl_a008585_set_next_event(ARCH_TIMER_VIRT_ACCESS, evt, clk);
> +	erratum_set_next_event(ARCH_TIMER_VIRT_ACCESS, evt, clk);
>  	return 0;
>  }
>  
> -static int fsl_a008585_set_next_event_phys(unsigned long evt,
> +static int erratum_set_next_event_phys(unsigned long evt,
>  					   struct clock_event_device *clk)
>  {
> -	fsl_a008585_set_next_event(ARCH_TIMER_PHYS_ACCESS, evt, clk);
> +	erratum_set_next_event(ARCH_TIMER_PHYS_ACCESS, evt, clk);
>  	return 0;
>  }
> -#endif /* CONFIG_FSL_ERRATUM_A008585 */
> +#endif
>  
>  static int arch_timer_set_next_event_virt(unsigned long evt,
>  					  struct clock_event_device *clk)
> @@ -350,16 +390,16 @@ static int arch_timer_set_next_event_phys_mem(unsigned long evt,
>  	return 0;
>  }
>  
> -static void fsl_a008585_set_sne(struct clock_event_device *clk)
> +static void erratum_set_sne(struct clock_event_device *clk)
>  {
> -#ifdef CONFIG_FSL_ERRATUM_A008585
> +#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
>  	if (!static_branch_unlikely(&arch_timer_read_ool_enabled))
>  		return;
>  
>  	if (arch_timer_uses_ppi == VIRT_PPI)
> -		clk->set_next_event = fsl_a008585_set_next_event_virt;
> +		clk->set_next_event = erratum_set_next_event_virt;
>  	else
> -		clk->set_next_event = fsl_a008585_set_next_event_phys;
> +		clk->set_next_event = erratum_set_next_event_phys;
>  #endif

This should be in the previous patch as well, as it only messes with the
FSL erratum.

>  }
>  
> @@ -392,7 +432,7 @@ static void __arch_timer_setup(unsigned type,
>  			BUG();
>  		}
>  
> -		fsl_a008585_set_sne(clk);
> +		erratum_set_sne(clk);
>  	} else {
>  		clk->features |= CLOCK_EVT_FEAT_DYNIRQ;
>  		clk->name = "arch_mem_timer";
> @@ -612,7 +652,7 @@ static void __init arch_counter_register(unsigned type)
>  
>  		clocksource_counter.archdata.vdso_direct = true;
>  
> -#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.
> @@ -899,12 +939,22 @@ static int __init arch_timer_of_init(struct device_node *np)
>  	arch_timer_c3stop = !of_property_read_bool(np, "always-on");
>  
>  #ifdef CONFIG_FSL_ERRATUM_A008585
> -	if (!erratum_workaround && of_property_read_bool(np, "fsl,erratum-a008585"))
> +	if (!erratum_workaround && of_property_read_bool(np, "fsl,erratum-a008585")) {
>  		erratum_workaround = &arch_timer_fsl_a008585;
> +		if (erratum_workaround) {

Brilliant!

> +			static_branch_enable(&arch_timer_read_ool_enabled);
> +			pr_info("Enabling workaround for FSL erratum A-008585\n");
> +		}
> +	}
> +#endif
>  
> -	if (erratum_workaround) {
> -		static_branch_enable(&arch_timer_read_ool_enabled);
> -		pr_info("Enabling workaround for FSL erratum A-008585\n");
> +#ifdef CONFIG_HISILICON_ERRATUM_161601
> +	if (!erratum_workaround && of_property_read_bool(np, "hisilicon,erratum-161601")) {
> +		erratum_workaround = &arch_timer_hisi_161601;
> +		if (erratum_workaround) {
> +			static_branch_enable(&arch_timer_read_ool_enabled);
> +			pr_info("Enabling workaround for HISILICON erratum 161601\n");
> +		}
>  	}
>  #endif

Do you see a pattern here? Surely you can factor a bit of that code (and
remove the nonsensical bits).

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

Re: [PATCH v2 3/4] arm64: arch_timer: Work around Erratum Hisilicon-161601

[Ding Tianhong]

On 2016/10/27 18:58, Marc Zyngier wrote:
> On 27/10/16 08:34, 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.
>>
>> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
>> ---
>>  Documentation/arm64/silicon-errata.txt |  1 +
>>  Documentation/kernel-parameters.txt    |  9 ++++
>>  arch/arm64/include/asm/arch_timer.h    | 28 ++++++++++-
>>  drivers/clocksource/Kconfig            | 14 +++++-
>>  drivers/clocksource/arm_arch_timer.c   | 88 ++++++++++++++++++++++++++--------
>>  5 files changed, 118 insertions(+), 22 deletions(-)
>>
>> diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt
>> index 405da11..70c5d5e 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      | Hip05/Hip06/Hip07 | #161601       | HISILICON_ERRATUM_161601|
> 
> I've already commented on the alignment. Please read my initial review.
> 

It sees misunderstood, fix it this time.

>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>> index 6fa1d8a..735b4b6 100644
>> --- a/Documentation/kernel-parameters.txt
>> +++ b/Documentation/kernel-parameters.txt
>> @@ -707,6 +707,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>>  			erratum.  If unspecified, the workaround is
>>  			enabled based on the device tree.
>>  
>> +	clocksource.arm_arch_timer.hisilicon-161601=
>> +			[ARM64]
>> +			Format: <bool>
>> +			Enable/disable the workaround of Hisilicon
>> +			erratum 161601.  This can be useful for KVM
>> +			guests, if the guest device tree doesn't show the
>> +			erratum.  If unspecified, the workaround is
>> +			enabled based on the device tree.
>> +
>>  	clearcpuid=BITNUM [X86]
>>  			Disable CPUID feature X for the kernel. See
>>  			arch/x86/include/asm/cpufeatures.h for the valid bit
>> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
>> index 118719d8..49b3041 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_timer_erratum_workaround() \
>>  	static_branch_unlikely(&arch_timer_read_ool_enabled)
>> @@ -65,11 +65,35 @@ extern struct arch_timer_erratum_workaround *erratum_workaround;
>>  	_new;						\
>>  })
>>  
>> +
>> +
>> +/*
>> + * The number of retries is an arbitrary value well beyond the highest number
>> + * of iterations the loop has been observed to take.
>> + * 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, 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.
>> + */
>> +#define __hisi_161601_read_reg(reg) ({				\
>> +	u64 _old, _new;						\
>> +	int _retries = 200;					\
> 
> Please document how this value was found (either in the code or in the
> commit message).

It really difficult to give the accurate standard, theoretically the error should not happened
twice together, so maybe 2 is enough here, I just give a arbitrary value.

> 
>> +								\
>> +	do {							\
>> +		_old = read_sysreg(reg);			\
>> +		_new = read_sysreg(reg);			\
>> +		_retries--;					\
>> +	} while (unlikely((_new - _old) >> 5) && _retries);	\
>> +								\
>> +	WARN_ON_ONCE(!_retries);				\
>> +	_new;							\
>> +})
> 
> Same remark as in the previous patch.
> 

I think the sentence *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* could explain why should *(_new - _old) >> 5*.
it is the same as (_new - _old)/32, also mean the _new should never bigger than _old more than 32.

>> +
>>  #define arch_timer_reg_read_stable(reg) 		\
>>  ({							\
>>  	u64 _val;					\
>>  	if (needs_timer_erratum_workaround())		\
>> -		_val = erratum_workaround->read_##reg();	\
>> +		_val = erratum_workaround->read_##reg();\
>>  	else						\
>>  		_val = read_sysreg(reg);		\
>>  	_val;						\
>> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
>> index 8a753fd..4aafb6a 100644
>> --- a/drivers/clocksource/Kconfig
>> +++ b/drivers/clocksource/Kconfig
>> @@ -312,8 +312,20 @@ config FSL_ERRATUM_A008585
>>  	help
>>  	  This option enables a workaround for Freescale/NXP Erratum
>>  	  A-008585 ("ARM generic timer may contain an erroneous
>> -	  value").  The workaround will only be active if the
>> +	  value").  The workaround will be active if the
>>  	  fsl,erratum-a008585 property is found in the timer node.
>> +	  This can be overridden with the clocksource.arm_arch_timer.fsl-a008585
>> +	  boot parameter.
> 
> Move this hunk to the previous patch.
> 
>> +
>> +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. This can be overridden with
>> +	  the clocksource.arm_arch_timer.hisilicon-161601 boot parameter.
>>  
>>  config ARM_GLOBAL_TIMER
>>  	bool "Support for the ARM global timer" if COMPILE_TEST
>> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
>> index e4f7fa1..89f1895 100644
>> --- a/drivers/clocksource/arm_arch_timer.c
>> +++ b/drivers/clocksource/arm_arch_timer.c
>> @@ -94,13 +94,14 @@ early_param("clocksource.arm_arch_timer.evtstrm", early_evtstrm_cfg);
>>   * Architected system timer support.
>>   */
>>  
>> -#ifdef CONFIG_FSL_ERRATUM_A008585
>> +#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
>>  struct arch_timer_erratum_workaround *erratum_workaround = NULL;
>>  
>>  DEFINE_STATIC_KEY_FALSE(arch_timer_read_ool_enabled);
>>  EXPORT_SYMBOL_GPL(arch_timer_read_ool_enabled);
>> +#endif
>>  
>> -
>> +#ifdef CONFIG_FSL_ERRATUM_A008585
>>  static u32 fsl_a008585_read_cntp_tval_el0(void)
>>  {
>>  	return __fsl_a008585_read_reg(cntp_tval_el0);
>> @@ -139,6 +140,45 @@ static int __init early_fsl_a008585_cfg(char *buf)
>>  early_param("clocksource.arm_arch_timer.fsl-a008585", early_fsl_a008585_cfg);
>>  #endif /* CONFIG_FSL_ERRATUM_A008585 */
>>  
>> +#ifdef CONFIG_HISILICON_ERRATUM_161601
>> +static u32 hisi_161601_read_cntp_tval_el0(void)
>> +{
>> +	return __hisi_161601_read_reg(cntp_tval_el0);
>> +}
>> +
>> +static  u32 hisi_161601_read_cntv_tval_el0(void)
>> +{
>> +	return __hisi_161601_read_reg(cntv_tval_el0);
>> +}
>> +
>> +static u64 hisi_161601_read_cntvct_el0(void)
>> +{
>> +	return __hisi_161601_read_reg(cntvct_el0);
>> +}
>> +
>> +static struct arch_timer_erratum_workaround arch_timer_hisi_161601 = {
>> +	.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,
>> +};
>> +
>> +static int __init early_hisi_161601_cfg(char *buf)
>> +{
>> +	int ret;
>> +	bool val;
>> +
>> +	ret = strtobool(buf, &val);
>> +	if (ret)
>> +		return ret;
>> +
>> +	if (val)
>> +		erratum_workaround = &arch_timer_hisi_161601;
>> +
>> +	return 0;
>> +}
>> +early_param("clocksource.arm_arch_timer.hisilicon-161601", early_hisi_161601_cfg);
>> +#endif /* CONFIG_HISILICON_ERRATUM_161601 */
>> +
>>  static __always_inline
>>  void arch_timer_reg_write(int access, enum arch_timer_reg reg, u32 val,
>>  			  struct clock_event_device *clk)
>> @@ -288,8 +328,8 @@ static __always_inline void set_next_event(const int access, unsigned long evt,
>>  	arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, clk);
>>  }
>>  
>> -#ifdef CONFIG_FSL_ERRATUM_A008585
>> -static __always_inline void fsl_a008585_set_next_event(const int access,
>> +#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
>> +static __always_inline void erratum_set_next_event(const int access,
>>  		unsigned long evt, struct clock_event_device *clk)
>>  {
>>  	unsigned long ctrl;
>> @@ -307,20 +347,20 @@ static __always_inline void fsl_a008585_set_next_event(const int access,
>>  	arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, clk);
>>  }
>>  
>> -static int fsl_a008585_set_next_event_virt(unsigned long evt,
>> +static int erratum_set_next_event_virt(unsigned long evt,
>>  					   struct clock_event_device *clk)
>>  {
>> -	fsl_a008585_set_next_event(ARCH_TIMER_VIRT_ACCESS, evt, clk);
>> +	erratum_set_next_event(ARCH_TIMER_VIRT_ACCESS, evt, clk);
>>  	return 0;
>>  }
>>  
>> -static int fsl_a008585_set_next_event_phys(unsigned long evt,
>> +static int erratum_set_next_event_phys(unsigned long evt,
>>  					   struct clock_event_device *clk)
>>  {
>> -	fsl_a008585_set_next_event(ARCH_TIMER_PHYS_ACCESS, evt, clk);
>> +	erratum_set_next_event(ARCH_TIMER_PHYS_ACCESS, evt, clk);
>>  	return 0;
>>  }
>> -#endif /* CONFIG_FSL_ERRATUM_A008585 */
>> +#endif
>>  
>>  static int arch_timer_set_next_event_virt(unsigned long evt,
>>  					  struct clock_event_device *clk)
>> @@ -350,16 +390,16 @@ static int arch_timer_set_next_event_phys_mem(unsigned long evt,
>>  	return 0;
>>  }
>>  
>> -static void fsl_a008585_set_sne(struct clock_event_device *clk)
>> +static void erratum_set_sne(struct clock_event_device *clk)
>>  {
>> -#ifdef CONFIG_FSL_ERRATUM_A008585
>> +#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601)
>>  	if (!static_branch_unlikely(&arch_timer_read_ool_enabled))
>>  		return;
>>  
>>  	if (arch_timer_uses_ppi == VIRT_PPI)
>> -		clk->set_next_event = fsl_a008585_set_next_event_virt;
>> +		clk->set_next_event = erratum_set_next_event_virt;
>>  	else
>> -		clk->set_next_event = fsl_a008585_set_next_event_phys;
>> +		clk->set_next_event = erratum_set_next_event_phys;
>>  #endif
> 
> This should be in the previous patch as well, as it only messes with the
> FSL erratum.
> 

Ok.

>>  }
>>  
>> @@ -392,7 +432,7 @@ static void __arch_timer_setup(unsigned type,
>>  			BUG();
>>  		}
>>  
>> -		fsl_a008585_set_sne(clk);
>> +		erratum_set_sne(clk);
>>  	} else {
>>  		clk->features |= CLOCK_EVT_FEAT_DYNIRQ;
>>  		clk->name = "arch_mem_timer";
>> @@ -612,7 +652,7 @@ static void __init arch_counter_register(unsigned type)
>>  
>>  		clocksource_counter.archdata.vdso_direct = true;
>>  
>> -#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.
>> @@ -899,12 +939,22 @@ static int __init arch_timer_of_init(struct device_node *np)
>>  	arch_timer_c3stop = !of_property_read_bool(np, "always-on");
>>  
>>  #ifdef CONFIG_FSL_ERRATUM_A008585
>> -	if (!erratum_workaround && of_property_read_bool(np, "fsl,erratum-a008585"))
>> +	if (!erratum_workaround && of_property_read_bool(np, "fsl,erratum-a008585")) {
>>  		erratum_workaround = &arch_timer_fsl_a008585;
>> +		if (erratum_workaround) {
> 
> Brilliant!
> 
>> +			static_branch_enable(&arch_timer_read_ool_enabled);
>> +			pr_info("Enabling workaround for FSL erratum A-008585\n");
>> +		}
>> +	}
>> +#endif
>>  
>> -	if (erratum_workaround) {
>> -		static_branch_enable(&arch_timer_read_ool_enabled);
>> -		pr_info("Enabling workaround for FSL erratum A-008585\n");
>> +#ifdef CONFIG_HISILICON_ERRATUM_161601
>> +	if (!erratum_workaround && of_property_read_bool(np, "hisilicon,erratum-161601")) {
>> +		erratum_workaround = &arch_timer_hisi_161601;
>> +		if (erratum_workaround) {
>> +			static_branch_enable(&arch_timer_read_ool_enabled);
>> +			pr_info("Enabling workaround for HISILICON erratum 161601\n");
>> +		}
>>  	}
>>  #endif
> 
> Do you see a pattern here? Surely you can factor a bit of that code (and
> remove the nonsensical bits).
> 

Yes, found it, try to fix it.

Thanks.
Ding

> Thanks,
> 
> 	M.
> 

Re: [PATCH v2 3/4] arm64: arch_timer: Work around Erratum Hisilicon-161601

[Marc Zyngier]

On 27/10/16 13:17, Ding Tianhong wrote:
> 
> 
> On 2016/10/27 18:58, Marc Zyngier wrote:
>> On 27/10/16 08:34, 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.
>>>
>>> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
>>> ---
>>>  Documentation/arm64/silicon-errata.txt |  1 +
>>>  Documentation/kernel-parameters.txt    |  9 ++++
>>>  arch/arm64/include/asm/arch_timer.h    | 28 ++++++++++-
>>>  drivers/clocksource/Kconfig            | 14 +++++-
>>>  drivers/clocksource/arm_arch_timer.c   | 88 ++++++++++++++++++++++++++--------
>>>  5 files changed, 118 insertions(+), 22 deletions(-)
>>>
>>> diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt
>>> index 405da11..70c5d5e 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      | Hip05/Hip06/Hip07 | #161601       | HISILICON_ERRATUM_161601|
>>
>> I've already commented on the alignment. Please read my initial review.
>>
> 
> It sees misunderstood, fix it this time.
> 
>>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>>> index 6fa1d8a..735b4b6 100644
>>> --- a/Documentation/kernel-parameters.txt
>>> +++ b/Documentation/kernel-parameters.txt
>>> @@ -707,6 +707,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>>>  			erratum.  If unspecified, the workaround is
>>>  			enabled based on the device tree.
>>>  
>>> +	clocksource.arm_arch_timer.hisilicon-161601=
>>> +			[ARM64]
>>> +			Format: <bool>
>>> +			Enable/disable the workaround of Hisilicon
>>> +			erratum 161601.  This can be useful for KVM
>>> +			guests, if the guest device tree doesn't show the
>>> +			erratum.  If unspecified, the workaround is
>>> +			enabled based on the device tree.
>>> +
>>>  	clearcpuid=BITNUM [X86]
>>>  			Disable CPUID feature X for the kernel. See
>>>  			arch/x86/include/asm/cpufeatures.h for the valid bit
>>> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
>>> index 118719d8..49b3041 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_timer_erratum_workaround() \
>>>  	static_branch_unlikely(&arch_timer_read_ool_enabled)
>>> @@ -65,11 +65,35 @@ extern struct arch_timer_erratum_workaround *erratum_workaround;
>>>  	_new;						\
>>>  })
>>>  
>>> +
>>> +
>>> +/*
>>> + * The number of retries is an arbitrary value well beyond the highest number
>>> + * of iterations the loop has been observed to take.
>>> + * 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, 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.
>>> + */
>>> +#define __hisi_161601_read_reg(reg) ({				\
>>> +	u64 _old, _new;						\
>>> +	int _retries = 200;					\
>>
>> Please document how this value was found (either in the code or in the
>> commit message).
> 
> It really difficult to give the accurate standard, theoretically the error should not happened
> twice together, so maybe 2 is enough here, I just give a arbitrary value.
> 
>>
>>> +								\
>>> +	do {							\
>>> +		_old = read_sysreg(reg);			\
>>> +		_new = read_sysreg(reg);			\
>>> +		_retries--;					\
>>> +	} while (unlikely((_new - _old) >> 5) && _retries);	\
>>> +								\
>>> +	WARN_ON_ONCE(!_retries);				\
>>> +	_new;							\
>>> +})
>>
>> Same remark as in the previous patch.
>>
> 
> I think the sentence *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* could explain why should *(_new - _old) >> 5*.
> it is the same as (_new - _old)/32, also mean the _new should never bigger than _old more than 32.

This is not about the explanation of the erratum, but about the location
of the #define, which can be made private to the .c file instead of
being globally visible.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

Re: [PATCH v2 3/4] arm64: arch_timer: Work around Erratum Hisilicon-161601

[Ding Tianhong]

On 2016/10/27 20:23, Marc Zyngier wrote:
> On 27/10/16 13:17, Ding Tianhong wrote:
>>
>>
>> On 2016/10/27 18:58, Marc Zyngier wrote:
>>> On 27/10/16 08:34, 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.
>>>>
>>>> Signed-off-by: Ding Tianhong <dingtianhong-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
>>>> ---
>>>>  Documentation/arm64/silicon-errata.txt |  1 +
>>>>  Documentation/kernel-parameters.txt    |  9 ++++
>>>>  arch/arm64/include/asm/arch_timer.h    | 28 ++++++++++-
>>>>  drivers/clocksource/Kconfig            | 14 +++++-
>>>>  drivers/clocksource/arm_arch_timer.c   | 88 ++++++++++++++++++++++++++--------
>>>>  5 files changed, 118 insertions(+), 22 deletions(-)
>>>>
>>>> diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt
>>>> index 405da11..70c5d5e 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      | Hip05/Hip06/Hip07 | #161601       | HISILICON_ERRATUM_161601|
>>>
>>> I've already commented on the alignment. Please read my initial review.
>>>
>>
>> It sees misunderstood, fix it this time.
>>
>>>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>>>> index 6fa1d8a..735b4b6 100644
>>>> --- a/Documentation/kernel-parameters.txt
>>>> +++ b/Documentation/kernel-parameters.txt
>>>> @@ -707,6 +707,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>>>>  			erratum.  If unspecified, the workaround is
>>>>  			enabled based on the device tree.
>>>>  
>>>> +	clocksource.arm_arch_timer.hisilicon-161601=
>>>> +			[ARM64]
>>>> +			Format: <bool>
>>>> +			Enable/disable the workaround of Hisilicon
>>>> +			erratum 161601.  This can be useful for KVM
>>>> +			guests, if the guest device tree doesn't show the
>>>> +			erratum.  If unspecified, the workaround is
>>>> +			enabled based on the device tree.
>>>> +
>>>>  	clearcpuid=BITNUM [X86]
>>>>  			Disable CPUID feature X for the kernel. See
>>>>  			arch/x86/include/asm/cpufeatures.h for the valid bit
>>>> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
>>>> index 118719d8..49b3041 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_timer_erratum_workaround() \
>>>>  	static_branch_unlikely(&arch_timer_read_ool_enabled)
>>>> @@ -65,11 +65,35 @@ extern struct arch_timer_erratum_workaround *erratum_workaround;
>>>>  	_new;						\
>>>>  })
>>>>  
>>>> +
>>>> +
>>>> +/*
>>>> + * The number of retries is an arbitrary value well beyond the highest number
>>>> + * of iterations the loop has been observed to take.
>>>> + * 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, 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.
>>>> + */
>>>> +#define __hisi_161601_read_reg(reg) ({				\
>>>> +	u64 _old, _new;						\
>>>> +	int _retries = 200;					\
>>>
>>> Please document how this value was found (either in the code or in the
>>> commit message).
>>
>> It really difficult to give the accurate standard, theoretically the error should not happened
>> twice together, so maybe 2 is enough here, I just give a arbitrary value.
>>
>>>
>>>> +								\
>>>> +	do {							\
>>>> +		_old = read_sysreg(reg);			\
>>>> +		_new = read_sysreg(reg);			\
>>>> +		_retries--;					\
>>>> +	} while (unlikely((_new - _old) >> 5) && _retries);	\
>>>> +								\
>>>> +	WARN_ON_ONCE(!_retries);				\
>>>> +	_new;							\
>>>> +})
>>>
>>> Same remark as in the previous patch.
>>>
>>
>> I think the sentence *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* could explain why should *(_new - _old) >> 5*.
>> it is the same as (_new - _old)/32, also mean the _new should never bigger than _old more than 32.
> 
> This is not about the explanation of the erratum, but about the location
> of the #define, which can be made private to the .c file instead of
> being globally visible.
> 

Ok, update it .

Thanks
Ding

> Thanks,
> 
> 	M.
> 

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Re: [PATCH v2 3/4] arm64: arch_timer: Work around Erratum Hisilicon-161601

[Will Deacon]

Hi Ding,

On Thu, Oct 27, 2016 at 03:34:10PM +0800, 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.
> 
> Signed-off-by: Ding Tianhong <dingtianhong-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
> ---

[...]

> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index 8a753fd..4aafb6a 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -312,8 +312,20 @@ config FSL_ERRATUM_A008585
>  	help
>  	  This option enables a workaround for Freescale/NXP Erratum
>  	  A-008585 ("ARM generic timer may contain an erroneous
> -	  value").  The workaround will only be active if the
> +	  value").  The workaround will be active if the
>  	  fsl,erratum-a008585 property is found in the timer node.
> +	  This can be overridden with the clocksource.arm_arch_timer.fsl-a008585
> +	  boot parameter.
> +
> +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. This can be overridden with
> +	  the clocksource.arm_arch_timer.hisilicon-161601 boot parameter.

I'm really not keen on having a kernel commandline parameter for this.
It's not something we've done for other, similar errata (e.g. CNTFRQ
reporting the wrong value) and I think it's a slippery slope to having
more of these workarounds controlled at boot-time. If you have a board
that is affected by this, it's always going to need the workaround. Why
would you turn it off?

Will
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Re: [PATCH v2 3/4] arm64: arch_timer: Work around Erratum Hisilicon-161601

[Ding Tianhong]

On 2016/10/29 0:00, Will Deacon wrote:
> Hi Ding,
> 
> On Thu, Oct 27, 2016 at 03:34:10PM +0800, 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.
>>
>> Signed-off-by: Ding Tianhong <dingtianhong-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
>> ---
> 
> [...]
> 
>> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
>> index 8a753fd..4aafb6a 100644
>> --- a/drivers/clocksource/Kconfig
>> +++ b/drivers/clocksource/Kconfig
>> @@ -312,8 +312,20 @@ config FSL_ERRATUM_A008585
>>  	help
>>  	  This option enables a workaround for Freescale/NXP Erratum
>>  	  A-008585 ("ARM generic timer may contain an erroneous
>> -	  value").  The workaround will only be active if the
>> +	  value").  The workaround will be active if the
>>  	  fsl,erratum-a008585 property is found in the timer node.
>> +	  This can be overridden with the clocksource.arm_arch_timer.fsl-a008585
>> +	  boot parameter.
>> +
>> +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. This can be overridden with
>> +	  the clocksource.arm_arch_timer.hisilicon-161601 boot parameter.
> 
> I'm really not keen on having a kernel commandline parameter for this.
> It's not something we've done for other, similar errata (e.g. CNTFRQ
> reporting the wrong value) and I think it's a slippery slope to having
> more of these workarounds controlled at boot-time. If you have a board
> that is affected by this, it's always going to need the workaround. Why
> would you turn it off?
> 

OK, miss it.

> Will
> 
> .
> 

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[PATCH v2 4/4] arm64: arch timer: Add timer erratum property for Hip05-d02 and Hip06-d03

[Ding Tianhong]

Enable workaround for hisilicon erratum 161601 on Hip05-d02 and Hip06-d03 board.

Signed-off-by: Ding Tianhong <dingtianhong-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
---
 arch/arm64/boot/dts/hisilicon/hip05.dtsi | 1 +
 arch/arm64/boot/dts/hisilicon/hip06.dtsi | 1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/arm64/boot/dts/hisilicon/hip05.dtsi b/arch/arm64/boot/dts/hisilicon/hip05.dtsi
index bf322ed..f815d94 100644
--- a/arch/arm64/boot/dts/hisilicon/hip05.dtsi
+++ b/arch/arm64/boot/dts/hisilicon/hip05.dtsi
@@ -281,6 +281,7 @@
 			     <GIC_PPI 14 IRQ_TYPE_LEVEL_LOW>,
 			     <GIC_PPI 11 IRQ_TYPE_LEVEL_LOW>,
 			     <GIC_PPI 10 IRQ_TYPE_LEVEL_LOW>;
+		hisilicon,erratum-161601;
 	};
 
 	pmu {
diff --git a/arch/arm64/boot/dts/hisilicon/hip06.dtsi b/arch/arm64/boot/dts/hisilicon/hip06.dtsi
index 5927bc4..d63990b 100644
--- a/arch/arm64/boot/dts/hisilicon/hip06.dtsi
+++ b/arch/arm64/boot/dts/hisilicon/hip06.dtsi
@@ -260,6 +260,7 @@
 			     <GIC_PPI 14 IRQ_TYPE_LEVEL_LOW>,
 			     <GIC_PPI 11 IRQ_TYPE_LEVEL_LOW>,
 			     <GIC_PPI 10 IRQ_TYPE_LEVEL_LOW>;
+		hisilicon,erratum-161601;
 	};
 
 	pmu {
-- 
1.9.0


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Re: [PATCH v2 1/4] arm64: arch_timer: Add device tree binding for hisilicon-161601 erratum

[Rob Herring]

On Thu, Oct 27, 2016 at 03:34:08PM +0800, Ding Tianhong wrote:
> This erratum describes a bug in logic outside the core, so MIDR can't be
> used to identify its presence, and reading an SoC-specific revision
> register from common arch timer code would be awkward.  So, describe it
> in the device tree.
> 
> v2: Use the new erratum name and update the description.
> 
> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
> ---
>  Documentation/devicetree/bindings/arm/arch_timer.txt | 8 ++++++++
>  1 file changed, 8 insertions(+)

Acked-by: Rob Herring <robh@kernel.org>