Re: [PATCH v9 4/9] clocksource/drivers/arm_arch_timer: use readq to get 64-bit CNTVCT

[Fu Wei]

Hi Will,

On 25 July 2016 at 23:31, Will Deacon <will.deacon@xxxxxxx> wrote:
> On Mon, Jul 25, 2016 at 11:27:02PM +0800, fu.wei@xxxxxxxxxx wrote:
>> From: Fu Wei <fu.wei@xxxxxxxxxx>
>>
>> This patch simplify arch_counter_get_cntvct_mem function by
>> using readq to get 64-bit CNTVCT value instead of readl_relaxed.
>>
>> Signed-off-by: Fu Wei <fu.wei@xxxxxxxxxx>
>> ---
>>  drivers/clocksource/arm_arch_timer.c | 10 +---------
>>  1 file changed, 1 insertion(+), 9 deletions(-)
>>
>> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
>> index e6fd42d..483d2f9 100644
>> --- a/drivers/clocksource/arm_arch_timer.c
>> +++ b/drivers/clocksource/arm_arch_timer.c
>> @@ -418,15 +418,7 @@ u32 arch_timer_get_rate(void)
>>
>>  static u64 arch_counter_get_cntvct_mem(void)
>>  {
>> -     u32 vct_lo, vct_hi, tmp_hi;
>> -
>> -     do {
>> -             vct_hi = readl_relaxed(arch_counter_base + CNTVCT_HI);
>> -             vct_lo = readl_relaxed(arch_counter_base + CNTVCT_LO);
>> -             tmp_hi = readl_relaxed(arch_counter_base + CNTVCT_HI);
>> -     } while (vct_hi != tmp_hi);
>> -
>> -     return ((u64) vct_hi << 32) | vct_lo;
>> +     return readq(arch_counter_base + CNTVCT_LO);
>
> Please drop this patch. It doesn't work.

I am OK to drop this, but could you let me know why it doesn't work?

I did get some problem on Foundation model about readq, but it works on Seattle.
I guess that is a problem of model, but not a code problem.
So I just got confused, why readq  doesn't work,  :-)


>
> http://lists.infradead.org/pipermail/linux-arm-kernel/2016-July/445369.html

I just replied to it, sorry.

>
> Will



-- 
Best regards,

Fu Wei
Software Engineer
Red Hat