[PATCH 5/6] powerpc/rtas: rename RTAS_RMOBUF_MAX to RTAS_USER_REGION_SIZE

[Alexey Kardashevskiy]

On 16/01/2021 02:56, Nathan Lynch wrote:
> Alexey Kardashevskiy <aik at ozlabs.ru> writes:
>> On 15/01/2021 09:00, Nathan Lynch wrote:
>>> diff --git a/arch/powerpc/include/asm/rtas.h b/arch/powerpc/include/asm/rtas.h
>>> index 332e1000ca0f..1aa7ab1cbc84 100644
>>> --- a/arch/powerpc/include/asm/rtas.h
>>> +++ b/arch/powerpc/include/asm/rtas.h
>>> @@ -19,8 +19,11 @@
>>>    #define RTAS_UNKNOWN_SERVICE (-1)
>>>    #define RTAS_INSTANTIATE_MAX (1ULL<<30) /* Don't instantiate rtas at/above this value */
>>>    
>>> -/* Buffer size for ppc_rtas system call. */
>>> -#define RTAS_RMOBUF_MAX (64 * 1024)
>>> +/* Work areas shared with RTAS must be 4K, naturally aligned. */
>>
>> Why exactly 4K and not (for example) PAGE_SIZE?
> 
> 4K is a platform requirement and isn't related to Linux's configured
> page size. See the PAPR specification for RTAS functions such as
> ibm,configure-connector, ibm,update-nodes, ibm,update-properties.

Good, since we are documenting things here - add to the comment ("per 
PAPR")?


> There are other calls with work area parameters where alignment isn't
> specified (e.g. ibm,get-system-parameter) but 4KB alignment is a safe
> choice for those.
> 
>>> +#define RTAS_WORK_AREA_SIZE   4096
>>> +
>>> +/* Work areas allocated for user space access. */
>>> +#define RTAS_USER_REGION_SIZE (RTAS_WORK_AREA_SIZE * 16)
>>
>> This is still 64K but no clarity why. There is 16 of something, what
>> is it?
> 
> There are 16 4KB work areas in the region. I can name it
> RTAS_NR_USER_WORK_AREAS or similar.


Why 16? PAPR (then add "per PAPR") or we just like 16 ("should be enough")?


-- 
Alexey