Re: [PATCH 2/9] ARC: timer: rtc: implement read loop in "C" vs. inline asm

[Vineet Gupta]

On 11/03/2016 10:02 AM, Daniel Lezcano wrote:
> On Mon, Oct 31, 2016 at 03:48:09PM -0700, Vineet Gupta wrote:
>> To allow for easy movement into drivers/clocksource
>>
>> Signed-off-by: Vineet Gupta 
>> ---
>>  arch/arc/kernel/time.c | 13 +
>>  1 file changed, 5 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/arc/kernel/time.c b/arch/arc/kernel/time.c
>> index a2db010cde18..2c51e3cafad0 100644
>> --- a/arch/arc/kernel/time.c
>> +++ b/arch/arc/kernel/time.c
>> @@ -153,14 +153,11 @@ static cycle_t arc_read_rtc(struct clocksource *cs)
>>  cycle_t  full;
>>  } stamp;
>>  
>> -
>> -__asm__ __volatile(
>> -"1: \n"
>> -"   lr  %0, [AUX_RTC_LOW]   \n"
>> -"   lr  %1, [AUX_RTC_HIGH]  \n"
>> -"   lr  %2, [AUX_RTC_CTRL]  \n"
>> -"   bbit0.nt%2, 31, 1b  \n"
>> -: "=r" (stamp.low), "=r" (stamp.high), "=r" (status));
>> +do {
>> +stamp.low = read_aux_reg(AUX_RTC_LOW);
>> +stamp.high = read_aux_reg(AUX_RTC_HIGH);
>> +status = read_aux_reg(AUX_RTC_CTRL);
>> +} while (!(status & 0x8000UL));
> 
> Replace the literal 0x8000UL by a macro.

OK !


> What is the 'status' for ?

Hardware keeps a internal state machine for atomic readout of low/high. So if an
interrupt is taken between reading low and high, or if high increments after low
is read, then the bit forces a loop to retry.

>   
>>  return stamp.full;
>>  }
>> -- 
>> 2.7.4
>>

Re: [PATCH 2/9] ARC: timer: rtc: implement read loop in "C" vs. inline asm

[Vineet Gupta]

On 11/03/2016 10:02 AM, Daniel Lezcano wrote:
> On Mon, Oct 31, 2016 at 03:48:09PM -0700, Vineet Gupta wrote:
>> To allow for easy movement into drivers/clocksource
>>
>> Signed-off-by: Vineet Gupta 
>> ---
>>  arch/arc/kernel/time.c | 13 +
>>  1 file changed, 5 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/arc/kernel/time.c b/arch/arc/kernel/time.c
>> index a2db010cde18..2c51e3cafad0 100644
>> --- a/arch/arc/kernel/time.c
>> +++ b/arch/arc/kernel/time.c
>> @@ -153,14 +153,11 @@ static cycle_t arc_read_rtc(struct clocksource *cs)
>>  cycle_t  full;
>>  } stamp;
>>  
>> -
>> -__asm__ __volatile(
>> -"1: \n"
>> -"   lr  %0, [AUX_RTC_LOW]   \n"
>> -"   lr  %1, [AUX_RTC_HIGH]  \n"
>> -"   lr  %2, [AUX_RTC_CTRL]  \n"
>> -"   bbit0.nt%2, 31, 1b  \n"
>> -: "=r" (stamp.low), "=r" (stamp.high), "=r" (status));
>> +do {
>> +stamp.low = read_aux_reg(AUX_RTC_LOW);
>> +stamp.high = read_aux_reg(AUX_RTC_HIGH);
>> +status = read_aux_reg(AUX_RTC_CTRL);
>> +} while (!(status & 0x8000UL));
> 
> Replace the literal 0x8000UL by a macro.

OK !


> What is the 'status' for ?

Hardware keeps a internal state machine for atomic readout of low/high. So if an
interrupt is taken between reading low and high, or if high increments after low
is read, then the bit forces a loop to retry.

>   
>>  return stamp.full;
>>  }
>> -- 
>> 2.7.4
>>

Re: [PATCH 2/9] ARC: timer: rtc: implement read loop in "C" vs. inline asm

[Daniel Lezcano]

On Mon, Oct 31, 2016 at 03:48:09PM -0700, Vineet Gupta wrote:
> To allow for easy movement into drivers/clocksource
> 
> Signed-off-by: Vineet Gupta 
> ---
>  arch/arc/kernel/time.c | 13 +
>  1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arc/kernel/time.c b/arch/arc/kernel/time.c
> index a2db010cde18..2c51e3cafad0 100644
> --- a/arch/arc/kernel/time.c
> +++ b/arch/arc/kernel/time.c
> @@ -153,14 +153,11 @@ static cycle_t arc_read_rtc(struct clocksource *cs)
>   cycle_t  full;
>   } stamp;
>  
> -
> - __asm__ __volatile(
> - "1: \n"
> - "   lr  %0, [AUX_RTC_LOW]   \n"
> - "   lr  %1, [AUX_RTC_HIGH]  \n"
> - "   lr  %2, [AUX_RTC_CTRL]  \n"
> - "   bbit0.nt%2, 31, 1b  \n"
> - : "=r" (stamp.low), "=r" (stamp.high), "=r" (status));
> + do {
> + stamp.low = read_aux_reg(AUX_RTC_LOW);
> + stamp.high = read_aux_reg(AUX_RTC_HIGH);
> + status = read_aux_reg(AUX_RTC_CTRL);
> + } while (!(status & 0x8000UL));

Replace the literal 0x8000UL by a macro.

What is the 'status' for ?
  
>   return stamp.full;
>  }
> -- 
> 2.7.4
> 

Re: [PATCH 2/9] ARC: timer: rtc: implement read loop in "C" vs. inline asm

[Daniel Lezcano]

On Mon, Oct 31, 2016 at 03:48:09PM -0700, Vineet Gupta wrote:
> To allow for easy movement into drivers/clocksource
> 
> Signed-off-by: Vineet Gupta 
> ---
>  arch/arc/kernel/time.c | 13 +
>  1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arc/kernel/time.c b/arch/arc/kernel/time.c
> index a2db010cde18..2c51e3cafad0 100644
> --- a/arch/arc/kernel/time.c
> +++ b/arch/arc/kernel/time.c
> @@ -153,14 +153,11 @@ static cycle_t arc_read_rtc(struct clocksource *cs)
>   cycle_t  full;
>   } stamp;
>  
> -
> - __asm__ __volatile(
> - "1: \n"
> - "   lr  %0, [AUX_RTC_LOW]   \n"
> - "   lr  %1, [AUX_RTC_HIGH]  \n"
> - "   lr  %2, [AUX_RTC_CTRL]  \n"
> - "   bbit0.nt%2, 31, 1b  \n"
> - : "=r" (stamp.low), "=r" (stamp.high), "=r" (status));
> + do {
> + stamp.low = read_aux_reg(AUX_RTC_LOW);
> + stamp.high = read_aux_reg(AUX_RTC_HIGH);
> + status = read_aux_reg(AUX_RTC_CTRL);
> + } while (!(status & 0x8000UL));

Replace the literal 0x8000UL by a macro.

What is the 'status' for ?
  
>   return stamp.full;
>  }
> -- 
> 2.7.4
>