[Ksummit-discuss] [CORE TOPIC] Mainline kernel on a cellphone
Linus Walleij
linus.walleij at linaro.org
Wed Aug 5 08:46:19 UTC 2015
On Wed, Aug 5, 2015 at 10:40 AM, Linus Walleij <linus.walleij at linaro.org> wrote:
> On Tue, Aug 4, 2015 at 12:36 AM, Marcel Holtmann <marcel at 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?
>> Some nasty solution here are to double stack the line disciplines and have
>> some sort of shared transport driver in between. I am trying to actually fix
>> that so that Bluetooth drivers can expose proper platform buses with
>> correctly assigned resources that the FM radio driver would just
>> enumerate on. So that part is in the works as well.
IIRC that was also suggested to us by Vitaly Wool when my
colleagues tried to mainline CG2900/STLC2690, so very very nice
to see this happening! Put me on CC when you post something,
not that it's my expert area but would be happy to help if I can.
Yours,
Linus Walleij
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