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Subject: Re: [PATCH 2/2] clocksource: arm_arch_timer: Correct fault
 programming of CNTKCTL_EL1.EVNTI
To:     Marc Zyngier <maz@kernel.org>
References: <20200817122415.6568-1-zhukeqian1@huawei.com>
 <20200817122415.6568-3-zhukeqian1@huawei.com>
 <b37f6cf6a660f51690f0689509650eed@kernel.org>
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        Andrew Jones <drjones@redhat.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
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        James Morse <james.morse@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
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From:   zhukeqian <zhukeqian1@huawei.com>
Message-ID: <519050e9-7a51-5621-6709-0c82d33456f6@huawei.com>
Date:   Tue, 18 Aug 2020 09:42:46 +0800
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Hi Marc,

On 2020/8/17 20:56, Marc Zyngier wrote:
> On 2020-08-17 13:24, 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.
>>
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
> 
> I have never given you this tag, you are making it up. Please read
> Documentation/process/submitting-patches.rst to understand what
> tag you can put by yourself.
Sorry about my mistake.
> 
> At best, put "Suggested-by" tag, as this is different from what
> I posted anyway.
OK, I will use this tag.

Thanks,
Keqian
> 
> Thanks,
> 
>         M.
> 
>> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
>> ---
>>  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 6e11c60..4140a37 100644
>> --- a/drivers/clocksource/arm_arch_timer.c
>> +++ b/drivers/clocksource/arm_arch_timer.c
>> @@ -794,10 +794,14 @@ 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--;
>>      /* enable event stream */
>>      arch_timer_evtstrm_enable(min(pos, 15));
>