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



Hi Oleksandr,

On 24/11/16 18:04, Oleksandr Andrushchenko wrote:
+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?

Regards,

--
Julien Grall

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