Re: trying to get qom-{get,set} working with gpio on qemu-x86_64

[Peter Maydell]

On Thu, 24 Feb 2022 at 10:53, Ben Dooks <ben.dooks@codethink.co.uk> wrote:
> I have been trying to get qom-get/qom-set scripts working to make an
> virtual GPIO device on qemu-system-x86_64. I have a working TMP105
> and I can see the MAX7310 being instantiated with the relevant Linux
> devices showing up (i2c, gpio).
>
> I can read the sensor from QEmu console:
>
> (qemu)  qom-get /machine/peripheral/sensor temperature
> 20000
> (qemu) qom-set  /machine/peripheral/sensor temperature 19000
> (qemu)  qom-get /machine/peripheral/sensor temperature
> 19000
>
> When trying to get or set anything from the GPIO chip it doesn't
> seem to be working. How do I get this working, I haven't found
> any useful reference online and need some help:
>
> (qemu) qom-set /machine/peripheral/gpio unnamed-gpio-out[0] 0
> Error: Device '0' not found
> (qemu) qom-set /machine/peripheral/gpio unnamed-gpio-in[0] 0
> Error: Insufficient permission to perform this operation

The 'unnamed-gpio-out/in' properties are part of the mechanism by
which a QEMU machine model can connect up GPIO lines of devices it
creates (for instance, it might connect a device's outbound GPIO
line to a GPIO controller). They appear in the monitor
qom-set/qom-get APIs because they use the same underlying
infrastructure as user-settable properties, but you can't do
anything useful with them on the command line.

If you need to wire up a device's GPIO lines, you need to do
it in C code as part of the QEMU machine model implementation.
Put another way,
  -device max7310,id=gpio,address=0x20
will work fine for "put a gpio controller at this i2c address,
so that guests that expect to be able to talk to one there
don't crash". You can't however actually wire up any of that
controller's GPIO lines to anything (emulated LEDs, other
devices, etc, etc).

> I am also having issues with both sensor and the gpio via the
> qom-set, as so:
>
> > $ sudo ./scripts/qmp/qom-set --socket ~/qmp.sock 
> > /machine/peripheral/sensor.temperature 20200
> > ExecuteError: Invalid parameter type for 'temperature', expected: integer
> > Task was destroyed but it is pending!
>
> Is this also a known issue?

I'm not sure what's going on there: it sounds like something
is confused about types. I've cc'd the python qmp scripts maintainer.

thanks
-- PMM