Re: [PATCH v2 2/2] clocksource: arm_arch_timer: Correct fault programming of CNTKCTL_EL1.EVNTI

2020-12-03 Thread zhukeqian 
Hi Marc,

On 2020/12/3 22:57, Marc Zyngier wrote:
> On 2020-08-18 04:28, 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.
>>
>> Fixes: 037f637767a8 ("drivers: clocksource: add support for
>>ARM architected timer event stream")
> 
> Fixes: tags should on a single line.
Will do.

> 
>> Suggested-by: Marc Zyngier 
>> Signed-off-by: Keqian Zhu 
>> ---
>>  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 777d38c..e3b2ee0 100644
>> --- a/drivers/clocksource/arm_arch_timer.c
>> +++ b/drivers/clocksource/arm_arch_timer.c
>> @@ -824,10 +824,14 @@ 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--;
> 
> You don't explain why you are special-casing pos == 1.
The logic is not clear here, I will try to reform it.

> 
>>  /* enable event stream */
>>  arch_timer_evtstrm_enable(min(pos, 15));
> 
> Also, please Cc the subsystem maintainers:
> 
> CLOCKSOURCE, CLOCKEVENT DRIVERS
> M:  Daniel Lezcano 
> M:  Thomas Gleixner 
> L:  linux-kernel@vger.kernel.org
> S:  Supported
> T:  git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 
> timers/core
> F:  Documentation/devicetree/bindings/timer/
> F:  drivers/clocksource/
> 
Will do.

> Thanks,
> 
> M.

Thanks,
Keqian

Re: [PATCH v2 2/2] clocksource: arm_arch_timer: Correct fault programming of CNTKCTL_EL1.EVNTI

2020-12-03 Thread Marc Zyngier 

On 2020-08-18 04:28, 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.

Fixes: 037f637767a8 ("drivers: clocksource: add support for
   ARM architected timer event stream")


Fixes: tags should on a single line.


Suggested-by: Marc Zyngier 
Signed-off-by: Keqian Zhu 
---
 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 777d38c..e3b2ee0 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -824,10 +824,14 @@ 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--;


You don't explain why you are special-casing pos == 1.


/* enable event stream */
arch_timer_evtstrm_enable(min(pos, 15));


Also, please Cc the subsystem maintainers:

CLOCKSOURCE, CLOCKEVENT DRIVERS
M:  Daniel Lezcano 
M:  Thomas Gleixner 
L:  linux-kernel@vger.kernel.org
S:  Supported
T:  git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 
timers/core

F:  Documentation/devicetree/bindings/timer/
F:  drivers/clocksource/

Thanks,

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

[PATCH v2 2/2] clocksource: arm_arch_timer: Correct fault programming of CNTKCTL_EL1.EVNTI

2020-08-17 Thread 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.

Fixes: 037f637767a8 ("drivers: clocksource: add support for
   ARM architected timer event stream")
Suggested-by: Marc Zyngier 
Signed-off-by: Keqian Zhu 
---
 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 777d38c..e3b2ee0 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -824,10 +824,14 @@ 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