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[PATCH v8 4/9] clocksource/drivers/arm_arch_timer: use readq to get 64-bit CNTVCT

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  [PATCH v8 4/9] clocksource/drivers/arm_arch_timer: use readq to get 64-bit CNTVCT fu.wei@linaro.org - 2016-07-19 20:20 +0200
    Re: [PATCH v8 4/9] clocksource/drivers/arm_arch_timer: use readq to  get 64-bit CNTVCT kbuild test robot <lkp@intel.com> - 2016-07-24 22:30 +0200
    Re: [PATCH v8 4/9] clocksource/drivers/arm_arch_timer: use readq to  get 64-bit CNTVCT Will Deacon <will.deacon@arm.com> - 2016-07-25 11:10 +0200
      Re: [PATCH v8 4/9] clocksource/drivers/arm_arch_timer: use readq to  get 64-bit CNTVCT Fu Wei <fu.wei@linaro.org> - 2016-07-25 18:00 +0200

#1446637 — [PATCH v8 4/9] clocksource/drivers/arm_arch_timer: use readq to get 64-bit CNTVCT

From: Fu Wei <fu.wei@linaro.org>

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@linaro.org>
---
 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);
 }
 
 /*
-- 
2.5.5

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#1449203 — Re: [PATCH v8 4/9] clocksource/drivers/arm_arch_timer: use readq to get 64-bit CNTVCT

[Multipart message — attachments visible in raw view] — view raw

Hi,

[auto build test ERROR on stable/master]
[cannot apply to tip/timers/core pm/linux-next next-20160724]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/fu-wei-linaro-org/acpi-clocksource-add-GTDT-driver-and-GTDT-support-in-arm_arch_timer/20160725-022614
base:   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git master
config: arm-sunxi_defconfig (attached as .config)
compiler: arm-linux-gnueabi-gcc (Debian 5.4.0-6) 5.4.0 20160609
reproduce:
        wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=arm 

All errors (new ones prefixed by >>):

   drivers/clocksource/arm_arch_timer.c: In function 'arch_counter_get_cntvct_mem':
>> drivers/clocksource/arm_arch_timer.c:421:9: error: implicit declaration of function 'readq' [-Werror=implicit-function-declaration]
     return readq(arch_counter_base + CNTVCT_LO);
            ^
   cc1: some warnings being treated as errors

vim +/readq +421 drivers/clocksource/arm_arch_timer.c

   415	{
   416		return arch_timer_rate;
   417	}
   418	
   419	static u64 arch_counter_get_cntvct_mem(void)
   420	{
 > 421		return readq(arch_counter_base + CNTVCT_LO);
   422	}
   423	
   424	/*

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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#1449387 — Re: [PATCH v8 4/9] clocksource/drivers/arm_arch_timer: use readq to get 64-bit CNTVCT

On Wed, Jul 20, 2016 at 02:17:59AM +0800, fu.wei@linaro.org wrote:
> From: Fu Wei <fu.wei@linaro.org>
> 
> 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@linaro.org>
> ---
>  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);

What's the benefit of doing this? If you use readq here, how can we
guarantee that (a) the endpoint won't generate a SLVERR or similar and
(b) that we get an atomic read?

"If it ain't broke, don't fix it"

Will

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#1449611 — Re: [PATCH v8 4/9] clocksource/drivers/arm_arch_timer: use readq to get 64-bit CNTVCT

Hi Will,

On 25 July 2016 at 17:02, Will Deacon <will.deacon@arm.com> wrote:
> On Wed, Jul 20, 2016 at 02:17:59AM +0800, fu.wei@linaro.org wrote:
>> From: Fu Wei <fu.wei@linaro.org>
>>
>> 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@linaro.org>
>> ---
>>  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);
>

Sorry, right after posting v9, I got your comment,

> What's the benefit of doing this? If you use readq here, how can we

benefit:
1. simplify the code
2. from arch/arm64/include/asm/io.h, I guess readq is more efficient

> guarantee that (a) the endpoint won't generate a SLVERR or similar and
> (b) that we get ?

I think so, according to arch/arm64/include/asm/io.h.
readq Implement by "LDR" and "LDAR", So I think It is an atomic read.

Please correct me, If I misunderstand something, thanks

>
> "If it ain't broke, don't fix it"
>
> Will



-- 
Best regards,

Fu Wei
Software Engineer
Red Hat

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