[PATCH 0/2] clocksource: arm_arch_timer: Some fixes and code adjustment

[PATCH 0/2] clocksource: arm_arch_timer: Some fixes and code adjustment

[Keqian Zhu]

During picking up pvtime LPT support for arm64, I found some trivial bugs for
arm arch_timer driver.

Keqian Zhu (2):
  clocksource: arm_arch_timer: Simplify and fix count reader code logic
  clocksource: arm_arch_timer: Correct fault programming of
    CNTKCTL_EL1.EVNTI

 arch/arm/include/asm/arch_timer.h    | 14 ++--------
 arch/arm64/include/asm/arch_timer.h  | 24 ++--------------
 drivers/clocksource/arm_arch_timer.c | 53 ++++++------------------------------
 3 files changed, 13 insertions(+), 78 deletions(-)

-- 
1.8.3.1

[PATCH 1/2] clocksource: arm_arch_timer: Simplify and fix count reader code logic

[Keqian Zhu]

In commit 0ea415390cd3 (clocksource/arm_arch_timer: Use arch_timer_read_counter
to access stable counters), we separate stable and normal count reader. Actually
the stable reader can correctly lead us to normal reader if we has no workaround.

Besides, in erratum_set_next_event_tval_generic(), we use normal reader, it is
obviously wrong, so just revert this commit to solve this problem by the way.

Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
---
 arch/arm/include/asm/arch_timer.h    | 14 ++----------
 arch/arm64/include/asm/arch_timer.h  | 24 ++------------------
 drivers/clocksource/arm_arch_timer.c | 43 ++----------------------------------
 3 files changed, 6 insertions(+), 75 deletions(-)

diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
index 9917581..d022614 100644
--- a/arch/arm/include/asm/arch_timer.h
+++ b/arch/arm/include/asm/arch_timer.h
@@ -84,7 +84,7 @@ static inline u32 arch_timer_get_cntfrq(void)
 	return val;
 }
 
-static inline u64 __arch_counter_get_cntpct(void)
+static inline u64 arch_counter_get_cntpct(void)
 {
 	u64 cval;
 
@@ -93,12 +93,7 @@ static inline u64 __arch_counter_get_cntpct(void)
 	return cval;
 }
 
-static inline u64 __arch_counter_get_cntpct_stable(void)
-{
-	return __arch_counter_get_cntpct();
-}
-
-static inline u64 __arch_counter_get_cntvct(void)
+static inline u64 arch_counter_get_cntvct(void)
 {
 	u64 cval;
 
@@ -107,11 +102,6 @@ static inline u64 __arch_counter_get_cntvct(void)
 	return cval;
 }
 
-static inline u64 __arch_counter_get_cntvct_stable(void)
-{
-	return __arch_counter_get_cntvct();
-}
-
 static inline u32 arch_timer_get_cntkctl(void)
 {
 	u32 cntkctl;
diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index 9f0ec21..08f7b0a 100644
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h
@@ -184,7 +184,7 @@ static inline void arch_timer_set_cntkctl(u32 cntkctl)
 	: "=r" (tmp) : "r" (_val));					\
 } while (0)
 
-static __always_inline u64 __arch_counter_get_cntpct_stable(void)
+static __always_inline u64 arch_counter_get_cntpct(void)
 {
 	u64 cnt;
 
@@ -194,17 +194,7 @@ static __always_inline u64 __arch_counter_get_cntpct_stable(void)
 	return cnt;
 }
 
-static __always_inline u64 __arch_counter_get_cntpct(void)
-{
-	u64 cnt;
-
-	isb();
-	cnt = read_sysreg(cntpct_el0);
-	arch_counter_enforce_ordering(cnt);
-	return cnt;
-}
-
-static __always_inline u64 __arch_counter_get_cntvct_stable(void)
+static __always_inline u64 arch_counter_get_cntvct(void)
 {
 	u64 cnt;
 
@@ -214,16 +204,6 @@ static __always_inline u64 __arch_counter_get_cntvct_stable(void)
 	return cnt;
 }
 
-static __always_inline u64 __arch_counter_get_cntvct(void)
-{
-	u64 cnt;
-
-	isb();
-	cnt = read_sysreg(cntvct_el0);
-	arch_counter_enforce_ordering(cnt);
-	return cnt;
-}
-
 #undef arch_counter_enforce_ordering
 
 static inline int arch_timer_arch_init(void)
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 6c3e841..6e11c60 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -150,26 +150,6 @@ u32 arch_timer_reg_read(int access, enum arch_timer_reg reg,
 	return val;
 }
 
-static notrace u64 arch_counter_get_cntpct_stable(void)
-{
-	return __arch_counter_get_cntpct_stable();
-}
-
-static notrace u64 arch_counter_get_cntpct(void)
-{
-	return __arch_counter_get_cntpct();
-}
-
-static notrace u64 arch_counter_get_cntvct_stable(void)
-{
-	return __arch_counter_get_cntvct_stable();
-}
-
-static notrace u64 arch_counter_get_cntvct(void)
-{
-	return __arch_counter_get_cntvct();
-}
-
 /*
  * Default to cp15 based access because arm64 uses this function for
  * sched_clock() before DT is probed and the cp15 method is guaranteed
@@ -383,8 +363,6 @@ static u32 notrace sun50i_a64_read_cntv_tval_el0(void)
 DEFINE_PER_CPU(const struct arch_timer_erratum_workaround *, timer_unstable_counter_workaround);
 EXPORT_SYMBOL_GPL(timer_unstable_counter_workaround);
 
-static atomic_t timer_unstable_counter_workaround_in_use = ATOMIC_INIT(0);
-
 static void erratum_set_next_event_tval_generic(const int access, unsigned long evt,
 						struct clock_event_device *clk)
 {
@@ -562,9 +540,6 @@ void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa
 			per_cpu(timer_unstable_counter_workaround, i) = wa;
 	}
 
-	if (wa->read_cntvct_el0 || wa->read_cntpct_el0)
-		atomic_set(&timer_unstable_counter_workaround_in_use, 1);
-
 	/*
 	 * Don't use the vdso fastpath if errata require using the
 	 * out-of-line counter accessor. We may change our mind pretty
@@ -625,14 +600,9 @@ static bool arch_timer_this_cpu_has_cntvct_wa(void)
 	return has_erratum_handler(read_cntvct_el0);
 }
 
-static bool arch_timer_counter_has_wa(void)
-{
-	return atomic_read(&timer_unstable_counter_workaround_in_use);
-}
 #else
 #define arch_timer_check_ool_workaround(t,a)		do { } while(0)
 #define arch_timer_this_cpu_has_cntvct_wa()		({false;})
-#define arch_timer_counter_has_wa()			({false;})
 #endif /* CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND */
 
 static __always_inline irqreturn_t timer_handler(const int access,
@@ -989,22 +959,13 @@ static void __init arch_counter_register(unsigned type)
 
 	/* Register the CP15 based counter if we have one */
 	if (type & ARCH_TIMER_TYPE_CP15) {
-		u64 (*rd)(void);
-
 		if ((IS_ENABLED(CONFIG_ARM64) && !is_hyp_mode_available()) ||
 		    arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI) {
-			if (arch_timer_counter_has_wa())
-				rd = arch_counter_get_cntvct_stable;
-			else
-				rd = arch_counter_get_cntvct;
+			arch_timer_read_counter = arch_counter_get_cntvct;
 		} else {
-			if (arch_timer_counter_has_wa())
-				rd = arch_counter_get_cntpct_stable;
-			else
-				rd = arch_counter_get_cntpct;
+			arch_timer_read_counter = arch_counter_get_cntpct;
 		}
 
-		arch_timer_read_counter = rd;
 		clocksource_counter.vdso_clock_mode = vdso_default;
 	} else {
 		arch_timer_read_counter = arch_counter_get_cntvct_mem;
-- 
1.8.3.1

[PATCH 2/2] clocksource: arm_arch_timer: Correct fault programming of CNTKCTL_EL1.EVNTI

[Keqian Zhu]

ARM virtual counter supports event stream, it can only trigger an event
when the trigger bit (the value of CNTKCTL_EL1.EVNTI) of CNTVCT_EL0 changes,
so the actual period of event stream is 2^(cntkctl_evnti + 1). For example,
when the trigger bit is 0, then virtual counter trigger an event for every
two cycles.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
---
 drivers/clocksource/arm_arch_timer.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 6e11c60..4140a37 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -794,10 +794,14 @@ static void arch_timer_configure_evtstream(void)
 {
 	int evt_stream_div, pos;
 
-	/* Find the closest power of two to the divisor */
-	evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ;
+	/*
+	 * Find the closest power of two to the divisor. As the event
+	 * stream can at most be generated at half the frequency of the
+	 * counter, use half the frequency when computing the divider.
+	 */
+	evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ / 2;
 	pos = fls(evt_stream_div);
-	if (pos > 1 && !(evt_stream_div & (1 << (pos - 2))))
+	if ((pos == 1) || (pos > 1 && !(evt_stream_div & (1 << (pos - 2)))))
 		pos--;
 	/* enable event stream */
 	arch_timer_evtstrm_enable(min(pos, 15));
-- 
1.8.3.1

Re: [PATCH 1/2] clocksource: arm_arch_timer: Simplify and fix count reader code logic

[Marc Zyngier]

On 2020-08-17 13:24, Keqian Zhu wrote:
> In commit 0ea415390cd3 (clocksource/arm_arch_timer: Use 
> arch_timer_read_counter
> to access stable counters), we separate stable and normal count reader. 
> Actually
> the stable reader can correctly lead us to normal reader if we has no
> workaround.

Resulting in an unnecessary overhead on non-broken systems that can run
without CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND. Not happening.

> Besides, in erratum_set_next_event_tval_generic(), we use normal 
> reader, it is
> obviously wrong, so just revert this commit to solve this problem by 
> the way.

If you want to fix something, post a patch that does exactly that.

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

Re: [PATCH 2/2] clocksource: arm_arch_timer: Correct fault programming of CNTKCTL_EL1.EVNTI

[Marc Zyngier]

On 2020-08-17 13:24, Keqian Zhu wrote:
> ARM virtual counter supports event stream, it can only trigger an event
> when the trigger bit (the value of CNTKCTL_EL1.EVNTI) of CNTVCT_EL0 
> changes,
> so the actual period of event stream is 2^(cntkctl_evnti + 1). For 
> example,
> when the trigger bit is 0, then virtual counter trigger an event for 
> every
> two cycles.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>

I have never given you this tag, you are making it up. Please read
Documentation/process/submitting-patches.rst to understand what
tag you can put by yourself.

At best, put "Suggested-by" tag, as this is different from what
I posted anyway.

Thanks,

         M.

> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
> ---
>  drivers/clocksource/arm_arch_timer.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/clocksource/arm_arch_timer.c
> b/drivers/clocksource/arm_arch_timer.c
> index 6e11c60..4140a37 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -794,10 +794,14 @@ static void arch_timer_configure_evtstream(void)
>  {
>  	int evt_stream_div, pos;
> 
> -	/* Find the closest power of two to the divisor */
> -	evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ;
> +	/*
> +	 * Find the closest power of two to the divisor. As the event
> +	 * stream can at most be generated at half the frequency of the
> +	 * counter, use half the frequency when computing the divider.
> +	 */
> +	evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ / 2;
>  	pos = fls(evt_stream_div);
> -	if (pos > 1 && !(evt_stream_div & (1 << (pos - 2))))
> +	if ((pos == 1) || (pos > 1 && !(evt_stream_div & (1 << (pos - 2)))))
>  		pos--;
>  	/* enable event stream */
>  	arch_timer_evtstrm_enable(min(pos, 15));

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

Re: [PATCH 1/2] clocksource: arm_arch_timer: Simplify and fix count reader code logic

[zhukeqian]

Hi Marc,

On 2020/8/17 20:52, Marc Zyngier wrote:
> On 2020-08-17 13:24, Keqian Zhu wrote:
>> In commit 0ea415390cd3 (clocksource/arm_arch_timer: Use arch_timer_read_counter
>> to access stable counters), we separate stable and normal count reader. Actually
>> the stable reader can correctly lead us to normal reader if we has no
>> workaround.
> 
> Resulting in an unnecessary overhead on non-broken systems that can run
> without CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND. Not happening.
OK, so I got the purpose of that patch wrong.
> 
>> Besides, in erratum_set_next_event_tval_generic(), we use normal reader, it is
>> obviously wrong, so just revert this commit to solve this problem by the way.
> 
> If you want to fix something, post a patch that does exactly that.
> 
I will.

Thanks,
Keqian
>         M.

Re: [PATCH 2/2] clocksource: arm_arch_timer: Correct fault programming of CNTKCTL_EL1.EVNTI

[zhukeqian]

Hi Marc,

On 2020/8/17 20:56, Marc Zyngier wrote:
> On 2020-08-17 13:24, Keqian Zhu wrote:
>> ARM virtual counter supports event stream, it can only trigger an event
>> when the trigger bit (the value of CNTKCTL_EL1.EVNTI) of CNTVCT_EL0 changes,
>> so the actual period of event stream is 2^(cntkctl_evnti + 1). For example,
>> when the trigger bit is 0, then virtual counter trigger an event for every
>> two cycles.
>>
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
> 
> I have never given you this tag, you are making it up. Please read
> Documentation/process/submitting-patches.rst to understand what
> tag you can put by yourself.
Sorry about my mistake.
> 
> At best, put "Suggested-by" tag, as this is different from what
> I posted anyway.
OK, I will use this tag.

Thanks,
Keqian
> 
> Thanks,
> 
>         M.
> 
>> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
>> ---
>>  drivers/clocksource/arm_arch_timer.c | 10 +++++++---
>>  1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/clocksource/arm_arch_timer.c
>> b/drivers/clocksource/arm_arch_timer.c
>> index 6e11c60..4140a37 100644
>> --- a/drivers/clocksource/arm_arch_timer.c
>> +++ b/drivers/clocksource/arm_arch_timer.c
>> @@ -794,10 +794,14 @@ static void arch_timer_configure_evtstream(void)
>>  {
>>      int evt_stream_div, pos;
>>
>> -    /* Find the closest power of two to the divisor */
>> -    evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ;
>> +    /*
>> +     * Find the closest power of two to the divisor. As the event
>> +     * stream can at most be generated at half the frequency of the
>> +     * counter, use half the frequency when computing the divider.
>> +     */
>> +    evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ / 2;
>>      pos = fls(evt_stream_div);
>> -    if (pos > 1 && !(evt_stream_div & (1 << (pos - 2))))
>> +    if ((pos == 1) || (pos > 1 && !(evt_stream_div & (1 << (pos - 2)))))
>>          pos--;
>>      /* enable event stream */
>>      arch_timer_evtstrm_enable(min(pos, 15));
>