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
