Linux gnss driver SPI support?

Linux gnss driver SPI support?

[Tim Harvey]

Johan,

I have noticed you maintain a gnss receiver subsystem and according to
the device-tree binding Documentation it looks like it supports SPI
but I'm not seeing any code support for SPI. Am I missing something or
would that support need to be added for use?

Best regards,

Tim

Re: Linux gnss driver SPI support?

[Johan Hovold]

On Tue, Jan 05, 2021 at 10:23:43AM -0800, Tim Harvey wrote:
> Johan,
> 
> I have noticed you maintain a gnss receiver subsystem and according to
> the device-tree binding Documentation it looks like it supports SPI
> but I'm not seeing any code support for SPI. Am I missing something or
> would that support need to be added for use?

Correct, there are currently no drivers supporting SPI and hence no
shared implementation either like there is for UART interfaces.

The driver for your device would need to handle the SPI bits itself for
now. What kind of device is it?

Johan

Re: Linux gnss driver SPI support?

[Tim Harvey]

On Wed, Jan 6, 2021 at 3:21 AM Johan Hovold <johan@kernel.org> wrote:
>
> On Tue, Jan 05, 2021 at 10:23:43AM -0800, Tim Harvey wrote:
> > Johan,
> >
> > I have noticed you maintain a gnss receiver subsystem and according to
> > the device-tree binding Documentation it looks like it supports SPI
> > but I'm not seeing any code support for SPI. Am I missing something or
> > would that support need to be added for use?
>
> Correct, there are currently no drivers supporting SPI and hence no
> shared implementation either like there is for UART interfaces.
>
> The driver for your device would need to handle the SPI bits itself for
> now. What kind of device is it?

Johan,

It is the u-blox ZOE-M8Q which has a UART as well as SPI/I2C/SQI
interface. The particular board design we are working on is
unfortunately out of UART's which is why we were looking at connecting
it via SPI.

I did come across a posting about this [1] which uses a userspace app
that creates a spy to pty bridge but it seems like they ran into some
performance/latency issues.

Tim
[1] https://portal.u-blox.com/s/question/0D52p00008jOh43CAC/using-neo-m8p-over-spi-as-a-high-accuracy-time-source-with-chrony

Re: Linux gnss driver SPI support?

[Johan Hovold]

On Wed, Jan 06, 2021 at 12:17:01PM -0800, Tim Harvey wrote:
> On Wed, Jan 6, 2021 at 3:21 AM Johan Hovold <johan@kernel.org> wrote:

> > Correct, there are currently no drivers supporting SPI and hence no
> > shared implementation either like there is for UART interfaces.
> >
> > The driver for your device would need to handle the SPI bits itself for
> > now. What kind of device is it?

> It is the u-blox ZOE-M8Q which has a UART as well as SPI/I2C/SQI
> interface. The particular board design we are working on is
> unfortunately out of UART's which is why we were looking at connecting
> it via SPI.

So we'd need to add support for the SPI interface to the ublox driver,
which is currently UART only.

> I did come across a posting about this [1] which uses a userspace app
> that creates a spy to pty bridge but it seems like they ran into some
> performance/latency issues.

Yeah, that is one of the problems that the gnss subsystem is meant to
solve; to handle the transport interface in the kernel and provide a
generic interface to user space.

Johan