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

[Samuel Ortiz <sameo@linux.intel.com>]

On Wed, Aug 05, 2015 at 10:46:19AM +0200, Linus Walleij wrote:
> On Wed, Aug 5, 2015 at 10:40 AM, Linus Walleij <linus.walleij@linaro.org> wrote:
> > On Tue, Aug 4, 2015 at 12:36 AM, Marcel Holtmann <marcel@holtmann.org> wrote:
> (...)
> >> In a perfect world I would prefer we are not using the Bluetooth HCI line discipline
> >> at all. The problem right now is that everybody wants to enable the UART as
> >> /dev/ttyFOO and then move on. However in reality they are not general purpose
> >> TTY devices. The only thing you can ever do with them is tell the Bluetooth
> >> subsystem that there is a TTY device and attach its line discipline to it.
> >
> > This is done from userspace right? I never managed to wrap my head around
> > this because it seemed so odd and plainly hackish.
> >
> > In this ST-Ericsson driver for CG2900:
> > http://marc.info/?l=linux-kernel&m=134873373526049&w=2
> > the HCI link is used to tunnel things that are not Bluetooth, also
> > GPS and FM radio is controlled over HCI. Yeah sorry, I didn't invent
> > it... the HCI is then run over a UART.
> 
> Damned I snapped off the latter part of your message. Typing and
> mailing to quickly. This was obviously in response to:
> 
> >> Or and did I mention that some manufactures actually put FM radio and GPS
> >> controls behind the Bluetooth chip. So access to these slave devices goes
> >> via the Bluetooth HCI. This means that you have this fun dependency:
> >>
> >> FM radio -> Bluetooth HCI -> UART -> UART slave
> 
> So what I wanted to ask is who else is doing this apart from
> CG2900/STLC2690? Is it a common pattern?
Unfortunately it seems to be a common pattern. TI combos used to do
that at well.

Cheers,
Samuel.