Hi Marc,
are you fine with this patch ?
On 04/12/2020 08:31, 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")
> Suggested-by: Marc Zyngier <maz@xxxxxxxxxx>
> Signed-off-by: Keqian Zhu <zhukeqian1@xxxxxxxxxx>
> ---
> drivers/clocksource/arm_arch_timer.c | 23 ++++++++++++++++-------
> 1 file changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 777d38cb39b0..d0177824c518 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -822,15 +822,24 @@ static void arch_timer_evtstrm_enable(int divider)
>
> static void arch_timer_configure_evtstream(void)
> {
> - int evt_stream_div, pos;
> + int evt_stream_div, lsb;
> +
> + /*
> + * 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;
> +
> + /*
> + * Find the closest power of two to the divisor. If the adjacent bit
> + * of lsb (last set bit, starts from 0) is set, then we use (lsb + 1).
> + */
> + lsb = fls(evt_stream_div) - 1;
> + if (lsb > 0 && (evt_stream_div & BIT(lsb - 1)))
> + lsb++;
>
> - /* 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))))
> - pos--;
> /* enable event stream */
> - arch_timer_evtstrm_enable(min(pos, 15));
> + arch_timer_evtstrm_enable(max(0, min(lsb, 15)));
> }
>
> static void arch_counter_set_user_access(void)
>
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