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

[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 <maz@xxxxxxxxxx>
>> Signed-off-by: Keqian Zhu <zhukeqian1@xxxxxxxxxx>
>> ---
>>  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 <daniel.lezcano@xxxxxxxxxx>
> M:      Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> L:      linux-kernel@xxxxxxxxxxxxxxx
> 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