Re: HCI over SPI support

[Johan Hedberg <johan.hedberg@gmail.com>]

Hi Ivan,

On Tue, Aug 08, 2017, Ivan Drobyshevskyi wrote:
> I need to get BlueZ working with KW30Z chip on a custom ARM board.
> It's strongly preferred to use SPI for HCI, since UART is needed for
> another purpose, but it looks HCI over SPI is not implemented in
> kernel. After some digging, it seems like the following options might
> work:
> 
> 1) Implement HCI over SPI in drivers/bluetooth, similarly to hci_uart.
> 2) use hci_vhci and make a (userspace) bridge app that would forward
> traffic between vhci and spi device. I found a python example for some
> unsupported chip connected over UART.
> 3) Implement some kind of adapter between UART and SPI (fake UART
> device), and use hci_uart.
> 
> What is the best/recommended way? It looks like the first option is
> the cleanest one, with some upstreaming potential, but it might
> involve much more work than the second one.

I'd go for proper kernel-side driver.

> On a related note, why is SPI is rarely, if at all, used for HCI?

Because SPI is not a standard HCI transport (something specified as part
of the Bluetooth Core Specification). So if you make a kernel-side
driver you need to be aware that it may not become the only SPI HCI
driver as the implementation will be vendor-specific rather than
standard.

Johan