[Suggestion] ARM64: kernel: compiling issue, need implement cmpxchg64 with assembler language.

Commit Message

Chen Gang April 20, 2013, 2:28 a.m. UTC

On 2013?04?19? 20:12, Arnd Bergmann wrote:
> On Friday 19 April 2013, Chen Gang wrote:
>> in arch/arm64/include/asm, not define the function cmpxchg64
>>
>>   when compiling with allmodconfig,
>>     drivers/block/blockconsole.c will need this function.
>>
>>   I am not quite familiar with ARM64 (neither ARM64 assembler)
>>
>>   can any member helps to send related patch ?
>>     if no one have time to send related patch, I should try.
>>     and I am glad to try, but need additional time resources,
>>     if I try, I should finish it within this month (2013-4-30).
>>
>>   welcome any suggestions or completions.
> 
> cmpxchg64 is the same as cmpxchg on 64-bit platforms, can't the
> driver be changed to use the latter?
> 
> 	Arnd
> 
> 

  can we be sure that cmpxchg64 is equal to cmpchg on all 64-bit platforms ?
    (I guess, the driver may need cross multiple platforms)
    (it seems, under x86, s390, better use cmpxchg64, at least they define it).

  whether we can be sure or not,
    I still prefer to define the macro cmpxchg64 just the alias of cmpxchg.
      (and I also guess ARM64 is always on 64-bit platform)

  the related patch may be like below.

-------------------------------patch begin--------------------------------------


-------------------------------patch end----------------------------------------



  I think, we can also reference the implementation of s390:
    it is in arch/s390/include/asm/cmpxchg.h.
    since we are ARM64, excluding ARM(32,16...), we can only consider 64-bit.
    if in the future, ARM64 and ARM are merged together:
      we can use CONFIG_64BIT to switch the cmpxchg64 definition.
      if define CONFIG_64BIT, use cmpxchg instead of cmpxchg64.
      else, use the definition of ARM (arch/arm/include/asm/cmpxchg.h already defines cmpxchg64)

-------------------------------reference begin----------------------------------

#ifdef CONFIG_64BIT
#define cmpxchg64(ptr, o, n)						\
({									\
	cmpxchg((ptr), (o), (n));					\
})
#else /* CONFIG_64BIT */
...
-------------------------------reference end------------------------------------

  :-)

Comments

Arnd Bergmann April 20, 2013, 7:32 a.m. UTC | #1

On Saturday 20 April 2013 10:28:55 Chen Gang wrote:
> 
> -------------------------------patch begin--------------------------------------
> 
> diff --git a/arch/arm64/include/asm/cmpxchg.h b/arch/arm64/include/asm/cmpxchg.h
> index 968b5cb..b572d2b 100644
> --- a/arch/arm64/include/asm/cmpxchg.h
> +++ b/arch/arm64/include/asm/cmpxchg.h
> @@ -170,4 +170,6 @@ static inline unsigned long __cmpxchg_mb(volatile void *ptr, unsigned long old,
>                                        (unsigned long)(n),              \
>                                        sizeof(*(ptr))))
>  
> +#define cmpxchg64(ptr,o,n)     cmpxchg((ptr),(o),(n))
> +
>  #endif /* __ASM_CMPXCHG_H */

Yes, this looks good. Please provide the same for cmpxchg64_local.

> -------------------------------patch end----------------------------------------
> 
> 
> 
>   I think, we can also reference the implementation of s390:
>     it is in arch/s390/include/asm/cmpxchg.h.
>     since we are ARM64, excluding ARM(32,16...), we can only consider 64-bit.
>     if in the future, ARM64 and ARM are merged together:
>       we can use CONFIG_64BIT to switch the cmpxchg64 definition.
>       if define CONFIG_64BIT, use cmpxchg instead of cmpxchg64.
>       else, use the definition of ARM (arch/arm/include/asm/cmpxchg.h already defines cmpxchg64)

I would not worry aobut merging the two at the moment.

> -------------------------------reference begin----------------------------------
> 
> #ifdef CONFIG_64BIT
> #define cmpxchg64(ptr, o, n)                                            \
> ({                                                                      \
>         cmpxchg((ptr), (o), (n));                                       \
> })
> #else /* CONFIG_64BIT */
> ...
> -------------------------------reference end------------------------------------

This implementation in unnecessarily verbose, I think the one you have
above is nicer.

	Arnd

Chen Gang April 22, 2013, 5:08 a.m. UTC | #2

On 2013?04?20? 15:32, Arnd Bergmann wrote:
> On Saturday 20 April 2013 10:28:55 Chen Gang wrote:
>>
>> -------------------------------patch begin--------------------------------------
>>
>> diff --git a/arch/arm64/include/asm/cmpxchg.h b/arch/arm64/include/asm/cmpxchg.h
>> index 968b5cb..b572d2b 100644
>> --- a/arch/arm64/include/asm/cmpxchg.h
>> +++ b/arch/arm64/include/asm/cmpxchg.h
>> @@ -170,4 +170,6 @@ static inline unsigned long __cmpxchg_mb(volatile void *ptr, unsigned long old,
>>                                        (unsigned long)(n),              \
>>                                        sizeof(*(ptr))))
>>  
>> +#define cmpxchg64(ptr,o,n)     cmpxchg((ptr),(o),(n))
>> +
>>  #endif /* __ASM_CMPXCHG_H */
> 
> Yes, this looks good. Please provide the same for cmpxchg64_local.
> 

  ok, thanks, I will send related patch.


gchen.

Patch

diff --git a/arch/arm64/include/asm/cmpxchg.h b/arch/arm64/include/asm/cmpxchg.h
index 968b5cb..b572d2b 100644
--- a/arch/arm64/include/asm/cmpxchg.h
+++ b/arch/arm64/include/asm/cmpxchg.h
@@ -170,4 +170,6 @@  static inline unsigned long __cmpxchg_mb(volatile void *ptr, unsigned long old,
 				       (unsigned long)(n),		\
 				       sizeof(*(ptr))))
 
+#define cmpxchg64(ptr,o,n)	cmpxchg((ptr),(o),(n))
+
 #endif	/* __ASM_CMPXCHG_H */