[Sound-open-firmware] can stream-box size be 0?

[Guennadi Liakhovetski]

On Wed, Apr 03, 2019 at 03:56:22PM +0100, Liam Girdwood wrote:
> On Wed, 2019-04-03 at 16:49 +0200, Guennadi Liakhovetski wrote:
> > On Wed, Apr 03, 2019 at 03:39:02PM +0100, Liam Girdwood wrote:
> > > On Wed, 2019-04-03 at 15:33 +0200, Guennadi Liakhovetski wrote:
> > > > Hi,
> > > > 
> > > > In kernel ipc.c I see "if (sdev->stream_box.size == 0)" checks at
> > > > exactly 4 locations, but all currently supported by SOF platforms set
> > > > the size to 0x200. Do we need those checks or can we safely assume, that
> > > > the size is never 0?
> > > 
> > > The size can depend on FW platform and how much space they allocate for
> > > mmap()
> > > stream position information. i.e. ALSA can read pipeline stream position
> > > stats
> > > directly from mailbox rather than via IPC.
> > 
> > Does that mean, that I misunderstood something? Could you point me out
> > to the code, that can set that size to anything other than 0x200, as
> > supplied by the firmware?
> > 
> 
> This size can be anything, even 0 is valid. Look at the extended boot data sent
> by the FW at boot in platform.c (e.g. src/platform/baytrail/platform.c)

Ok, right, I understand that. BTW, a correction: it's actually 0x1000
(4096) on cAVS platforms. But anyway: I understand that it's
configurable by the firmware and at least in theory it's allowed to be
0. But do we have any platforms where it is 0? I don't see any. Have we
ever tested such a case? The kernel has code that checks it for 0 (see
above), but if we don't have any such platforms it means, those paths
are never entered and never tested. Looking at them their handling also
doesn't seem entirely clear to me. So my question is: do we really want
and need to be able at least in theory to use 0 there and keep that code
and hope, that it works and never breaks, or can we remove that code and
put a check and an failure if it's 0?

Thanks
Guennadi