Re: [Ksummit-discuss] [TECH TOPIC] mobile phones

[Pavel Machek <pavel@ucw.cz>]

[-- Attachment #1: Type: text/plain, Size: 2698 bytes --]

On Mon 2017-06-26 12:49:46, Mark Brown wrote:
> On Mon, Jun 26, 2017 at 01:14:22PM +0200, Pavel Machek wrote:
> 
> > > Do you have some more specific concern?  This already works basically
> > > fine upstream, we happily support off-SoC audio paths.  The digital
> > > configuration could do with being more flexible but it works and people
> > > ship it.  It would be awfully nice to have some control/visibility of
> > > the modem side but that's just a missing driver problem.
> 
> > Well, I was told gsm audio is different, because it is packetized, has
> > additional timing info, and does not transmit silence.
> 
> Those things are true, however this is all handled inside the modem so
> nothing else in the system sees anything there.  Even if we were to see
> things this is pretty much just VoIP over a funny carrier (some of the
> 4G standards are just SIP AIUI) which isn't too hard.

I'm still asking for one example of system that's properly designed
according to you.

It may be "VoIP over funny carrier" -- but how do you suggest we
handle it? ALSA is for soundcards, not for VoIP so maybe
/dev/cmtspeech is okay after all?

> > So we have /dev/cmtspeech instead of second sound card.
> 
> That's just whatever random thing you're working on.  It really
> shouldn't be a second sound card on a well designed system, the phone
> audio generally doesn't go anywhere near the CPU for latency reasons so
> the whole system is one sound card.

First, where can I buy example of such well-designed system?

Second, no I can't agree. I certainly don't want baseband CPU to talk
directly to my speakers/microphone, for security reasons. Then there's
an option to process the sound between sending it over GSM, record
calls, etc. I quite like the flexibility, too. Latency problems are
solveable in software -- N900 with Maemo has reasonable call quality.

Third, I already have the system, I'm asking how to support it cleanly.

> > Is there any GSM audio driver that actually uses sound framework
> > properly?
> 
> The modems tend to just be stub drivers to Linux as the audio port
> doesn't vary configuration at runtime but I'd be a bit surprised if a
> modern phone wasn't broadly aiming towards the right thing, this stuff
> started appearing in flagship devices in about 2012.  The speyside
> system in mainline isn't actually a phone but models what's going on.

Well, the flagship devices are have 1000000+ lines of diffs relative
to mainline, due to Qualcomm, right? :-(.

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 181 bytes --]