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

Linus Walleij linus.walleij at linaro.org
Wed Aug 5 08:40:11 UTC 2015


On Tue, Aug 4, 2015 at 12:36 AM, Marcel Holtmann <marcel at holtmann.org> wrote:
> Hi Rob,

>> There's been some work by Neil Brown to create a UART slave
>> bus[1] (...)

> The work on UART slaves (or whatever it will be called eventually) is important
> for Bluetooth and most likely GPS and NFC in the future. It then allows to define
> all the nasty behind the curtain details of that UART via DT or ACPI in vendor drivers.

I agree 100%, and I think I have a simple enough in-kernel usecase so I can
get testing these series.

It seems GPS and NFC and other code is being kept out of the kernel
because of the absense of a UART slave bus and all the hazzle of handling
this.

> 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.

Yours,
Linus Walleij


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