| Message ID | 20201204073126.6920-3-zhukeqian1@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | clocksource: arm_arch_timer: Some fixes | expand |
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@kernel.org> > Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com> > --- > 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) >
Hi Daniel, On 2020-12-05 11:15, Daniel Lezcano wrote: > Hi Marc, > > are you fine with this patch ? I am, although there still isn't any justification for the pos/lsb rework in the commit message (and calling that variable lsb is somewhat confusing). If you are going to apply it, please consider adding the additional comment below. > > > 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. "While we're at it, rework the way we compute the trigger bit position by making it more obvious that when bits [n:n-1] are both set (with n being the most significant bit), we pick bit (n + 1)." With that: Acked-by: Marc Zyngier <maz@kernel.org> Thanks, M.
Hi Marc, On 05/12/2020 19:22, Marc Zyngier wrote: > Hi Daniel, > > On 2020-12-05 11:15, Daniel Lezcano wrote: >> Hi Marc, >> >> are you fine with this patch ? > > I am, although there still isn't any justification for the pos/lsb > rework in the commit message (and calling that variable lsb is somewhat > confusing). If you are going to apply it, please consider adding > the additional comment below. Ok, I will do that. Thanks for the additional comment -- Daniel >> 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. > > "While we're at it, rework the way we compute the trigger bit position by > making it more obvious that when bits [n:n-1] are both set (with n being > the most significant bit), we pick bit (n + 1)." > > With that: > > Acked-by: Marc Zyngier <maz@kernel.org> > > Thanks, > > M.
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)
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@kernel.org> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com> --- drivers/clocksource/arm_arch_timer.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-)