Re: [Ksummit-discuss] [CORE TOPIC] Mainline kernel on a cellphone

[Mark Brown <broonie@kernel.org>]

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On Fri, Jul 31, 2015 at 02:22:27PM +0200, Pavel Machek wrote:
> On Wed 2015-07-29 14:32:44, Mark Brown wrote:
> > On Thu, Jul 23, 2015 at 10:29:02PM +0200, Pavel Machek wrote:

> > ALSA is the right interface for this, this is going to be some
> > misunderstanding on their part about how to use it or limitations in

> That's what I was arguing, but see https://lkml.org/lkml/2015/3/5/606

I can't view that link since lkml.org was down earlier today when I was
working online and now I'm working offline.

> kai> Our take was that ALSA is not the right interface for cmt_speech. The
> kai> cmt_speech interface in the modem is _not_ a PCM interface as modelled
> kai> by
> kai> ALSA. Specifically:
> kai>
> kai>- the interface is lossy in both directions

Yay.

> kai>- data is sent in packets, not a stream of samples (could be other
> kai>- things
> kai>   than PCM samples), with timing and meta-data

This is what the copy() operation in the driver is for, there are other
DSP based devices out there as well as things like USB.

> kai>   - timing of uplink is of utmost importance

Well, ALSA doesn't impose any latency of its own so there should be no
issue there - the overheads should be minimal.

> > the drivers for their particular system (and possibly some unfortunate
> > hardware design, it sounds like they may still be bouncing the voice
> > call through the AP which isn't the most wonderful idea ever).
> > There

> Actually, sending data through AP is _very_ good idea from security
> perspective. You don't want hacked baseband to eavesdrop on you, do
> you?

Given that the baseband is a key part of the data path it's not like
you're gaining anything there as far as I can see?   I suppose you could
argue that the AP is actually an additional attack surface here.

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