Re: [Embedded-pv-devel] [PATCH v10] xen: add para-virtual sound interface header file

[Oleksandr Andrushchenko <andr2000@xxxxxxxxx>]

>>>>>>>>
>>>>>>>> +struct xensnd_close_req {
>>>>>>>> +};
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> I'm afraid structures without any members aren't permitted by C89.
>>>>>>>
>>>>>> There are 2 options I see:
>>>>>> 1. Remove empty structures
>>>>>> 2. Leave them in, but add a comment and add a dummy place holder
>>>>>> I would prefer option 1 as this way the interface seems to be clearer,
>>>>>> like all requests are defined etc.
>>>>
>>>>
>>>> Typo: I would prefer option 2 with placeholders and comments
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> +struct xensnd_request {
>>>>>>>> +     uint8_t raw[64];
>>>>>>>> +};
>>>>>>>> +
>>>>>>>> +struct xensnd_response {
>>>>>>>> +     uint8_t raw[64];
>>>>>>>> +};
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> What are these two needed for now? If you want to enforce a
>>>>>>> minimum size, that would better go ...
>>>>>>>
>>>>>> That is because we want to be cache line aligned.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> But this is only accurate to your platform. There is HW available with
>>>>> 128
>>>>> bytes.
>>>>>
>>>>> For instance on Xen ARM, all the structures are aligned to 128 bytes in
>>>>> order to fit in most of cache line. Although technically it would be
>>>>> possible have bigger one (see the definition of CSSIDR).
>>>>>
>>>> So, then I will align to 32
>>>
>>>
>>>
>>> To confirm, you don't plan to reduce the size of the command packet to 32
>>> octet?
>>>
>> Well, actually this is what I was going to do...
>> So, what is the correct value to be used here?
>
>
> I don't know. What is the expected maximum size of a command?
>
With the current design I don't expect it to be more than 32.
Actually we have already implemented a Linux PV snd driver
and feel comfortable with 32.
So, I would suggest we stick to 32
> Regards,
>
> --
> Julien Grall
-- 
Best regards,
Oleksandr Andrushchenko

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