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From: Alexey Kardashevskiy <aik@ozlabs.ru>
To: Nathan Lynch <nathanl@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org
Cc: tyreld@linux.ibm.com, brking@linux.ibm.com, ajd@linux.ibm.com,
	aneesh.kumar@linux.ibm.com
Subject: Re: [PATCH 5/6] powerpc/rtas: rename RTAS_RMOBUF_MAX to RTAS_USER_REGION_SIZE
Date: Mon, 18 Jan 2021 15:15:55 +1100	[thread overview]
Message-ID: <6905c3d2-e524-b6d8-036f-7812ea3f8b85@ozlabs.ru> (raw)
In-Reply-To: <87a6taxkgf.fsf@linux.ibm.com>



On 16/01/2021 02:56, Nathan Lynch wrote:
> Alexey Kardashevskiy <aik@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

  reply	other threads:[~2021-01-18  4:18 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-14 21:59 [PATCH 0/6] powerpc/rtas: miscellaneous cleanups, user region allocation Nathan Lynch
2021-01-14 21:59 ` [PATCH 1/6] powerpc/rtas: improve ppc_rtas_rmo_buf_show documentation Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15  5:50   ` Andrew Donnellan
2021-01-14 22:00 ` [PATCH 2/6] powerpc/rtas-proc: remove unused RMO_READ_BUF_MAX Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15  5:52   ` Andrew Donnellan
2021-01-14 22:00 ` [PATCH 3/6] powerpc/rtas: remove ibm_suspend_me_token Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15  5:52   ` Andrew Donnellan
2021-01-14 22:00 ` [PATCH 4/6] powerpc/rtas: move syscall filter setup into separate function Nathan Lynch
2021-01-15  4:39   ` Alexey Kardashevskiy
2021-01-15 16:04     ` Nathan Lynch
2021-01-15  5:49   ` Andrew Donnellan
2021-01-14 22:00 ` [PATCH 5/6] powerpc/rtas: rename RTAS_RMOBUF_MAX to RTAS_USER_REGION_SIZE Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15 15:56     ` Nathan Lynch
2021-01-18  4:15       ` Alexey Kardashevskiy [this message]
2021-01-20  1:17         ` Nathan Lynch
2021-01-20  5:05           ` Alexey Kardashevskiy
2021-01-21 15:17             ` Nathan Lynch
2021-01-15  6:10   ` Andrew Donnellan
2021-01-15 12:04   ` kernel test robot
2021-01-14 22:00 ` [PATCH 6/6] powerpc/rtas: constrain user region allocation to RMA Nathan Lynch
2021-01-15  4:38   ` Alexey Kardashevskiy
2021-01-15 15:38     ` Nathan Lynch
2021-01-18  4:12       ` Alexey Kardashevskiy
2021-01-20  0:39         ` Nathan Lynch
2021-01-20  4:49           ` Alexey Kardashevskiy
2021-01-20 12:06           ` Michael Ellerman
2021-01-21 15:27             ` Nathan Lynch
2021-01-23  1:54               ` Alexey Kardashevskiy
2021-01-19  9:00   ` Michael Ellerman
2021-01-19 21:00     ` Nathan Lynch
2021-01-20 12:13       ` Michael Ellerman
2021-01-21  0:26         ` Nathan Lynch

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