Re: [PATCH v20 08/17] clocksource/drivers/arm_arch_timer: Rework counter frequency detection.

Fu Wei
2017-01-19T09:44:46Z

Hi Hanjun,

On 19 January 2017 at 16:02, Hanjun Guo <hanjun.guo-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote:
> Hi Fuwei,
>
> One comments below.
>
>
> On 2017/1/18 21:25, fu.wei-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org wrote:
>>
>> From: Fu Wei <fu.wei-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
>>
>> The counter frequency detection call(arch_timer_detect_rate) combines two
>> ways to get counter frequency: system coprocessor register and MMIO timer.
>> But in a specific timer init code, we only need one way to try:
>> getting frequency from MMIO timer register will be needed only when we
>> init MMIO timer; getting frequency from system coprocessor register will
>> be needed only when we init arch timer.
>>
>> This patch separates paths to determine frequency:
>> Separate out the MMIO frequency and the sysreg frequency detection call,
>> and use the appropriate one for the counter.
>>
>> Signed-off-by: Fu Wei <fu.wei-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
>> ---
>> drivers/clocksource/arm_arch_timer.c | 40
>> ++++++++++++++++++++++--------------
>> 1 file changed, 25 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/clocksource/arm_arch_timer.c
>> b/drivers/clocksource/arm_arch_timer.c
>> index 6484f84..9482481 100644
>> --- a/drivers/clocksource/arm_arch_timer.c
>> +++ b/drivers/clocksource/arm_arch_timer.c
>> @@ -488,23 +488,33 @@ static int arch_timer_starting_cpu(unsigned int cpu)
>> return 0;
>> }
>>
>> -static void arch_timer_detect_rate(void __iomem *cntbase)
>> +static void __arch_timer_determine_rate(u32 rate)
>> {
>> - /* Who has more than one independent system counter? */
>> - if (arch_timer_rate)
>> - return;
>> + /* Check the timer frequency. */
>> + if (!arch_timer_rate) {
>> + if (rate)
>> + arch_timer_rate = rate;
>> + else
>> + pr_warn("frequency not available\n");
>> + } else if (rate && arch_timer_rate != rate) {
>
> ^
> Typo? I think it's "&" here.

Not a typo, It's definitely a “&&” :-)

Here arch_timer_rate is not zero.

If rate is not zero(that means we got a valid rate), and
arch_timer_rate != rate ,
we will print warning message.

>
> Thanks
> Hanjun

--
Best regards,

Fu Wei
Software Engineer
Red Hat
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