Hi Marc,
On 2020/7/28 18:16, Marc Zyngier wrote:
> On 2020-07-17 10:21, Keqian Zhu wrote:
>> ARM virtual counter supports event stream. It can only trigger an event
>> when the trigger bit of CNTVCT_EL0 changes from 0 to 1 (or from 1 to 0),
>> so the actual period of event stream is 2 ^ (cntkctl_evnti + 1). For
>> example, when the trigger bit is 0, then it triggers an event for every
>> two cycles.
>>
>> Signed-off-by: Keqian Zhu <zhukeqian1@xxxxxxxxxx>
>> ---
>> drivers/clocksource/arm_arch_timer.c | 17 ++++++++++++++---
>> 1 file changed, 14 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/clocksource/arm_arch_timer.c
>> b/drivers/clocksource/arm_arch_timer.c
>> index ecf7b7db2d05..06d99a4b1b9b 100644
>> --- a/drivers/clocksource/arm_arch_timer.c
>> +++ b/drivers/clocksource/arm_arch_timer.c
>> @@ -799,10 +799,20 @@ static void __arch_timer_setup(unsigned type,
>> static void arch_timer_evtstrm_enable(int divider)
>> {
>> u32 cntkctl = arch_timer_get_cntkctl();
>> + int cntkctl_evnti;
>> +
>> + /*
>> + * Note that it can only trigger an event when the trigger bit
>> + * of CNTVCT_EL0 changes from 1 to 0 (or from 0 to 1), so the
>> + * actual period of event stream is 2 ^ (cntkctl_evnti + 1).
>> + */
>> + cntkctl_evnti = divider - 1;
>> + cntkctl_evnti = min(cntkctl_evnti, 15);
>> + cntkctl_evnti = max(cntkctl_evnti, 0);
>>
>> cntkctl &= ~ARCH_TIMER_EVT_TRIGGER_MASK;
>> /* Set the divider and enable virtual event stream */
>> - cntkctl |= (divider << ARCH_TIMER_EVT_TRIGGER_SHIFT)
>> + cntkctl |= (cntkctl_evnti << ARCH_TIMER_EVT_TRIGGER_SHIFT)
>> | ARCH_TIMER_VIRT_EVT_EN;
>> arch_timer_set_cntkctl(cntkctl);
>> arch_timer_set_evtstrm_feature();
>> @@ -816,10 +826,11 @@ static void arch_timer_configure_evtstream(void)
>> /* Find the closest power of two to the divisor */
>> evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ;
>> 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));
>> + arch_timer_evtstrm_enable(pos);
>> }
>>
>> static void arch_counter_set_user_access(void)
>
> This looks like a very convoluted fix. If the problem you are
> trying to fix is that the event frequency is at most half of
> that of the counter, why isn't the patch below the most
> obvious fix?
>
> Thanks,
>
> M.
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 6c3e84180146..0a65414b781f 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -824,8 +824,12 @@ 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))))
I think here does not consider the case of pos==1 (though it will not occur...)
> pos--;
>
It looks good to me.
Thanks,
Keqian
