Re: [RFC 1/4] ASoC: topology: Add topology UAPI header.

[Mark Brown <broonie@kernel.org>]

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On Tue, Apr 21, 2015 at 01:43:47PM +0100, Liam Girdwood wrote:
> On Tue, 2015-04-21 at 12:02 +0200, Takashi Iwai wrote:
> > At Tue, 21 Apr 2015 10:47:53 +0100,

> > > > Not got a massively strong opinion here but given that we have ABI
> > > > versioning can we just skip the 128 bytes of reserved space in most of
> > > > the structs?  Doesn't seem to be doing much except making the files
> > > > bigger.

> > > We had a similar discussion in Nuremburg last week, the intention is to
> > > keep the size of the structures constant so wont dont break older
> > > kernels with newer userspace ABIs etc.

> > Maybe a question is whether the size is sensible.  But the argument
> > here was "memory is cheap nowadays".

> Ok, we can reduce the size here. I think Vinod wanted at least 4 * 4
> byte words (i.e. 16 bytes) minimum IIRC, what about 16 bytes ? That
> would give us at least 4 new members for the future ?

That's sounding like an awfully small number if we're trying to be
infititely future proof (obviously the default value for that is 640k!).
We'd also need to go through and give *all* the structures padding.  How
about just adding length fields instead with a rule that if the
structure is bigger than you know about just ignore anything at the end?

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