Re: [RFC PATCH] cli: add connect-gpios option

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Oct 18, 2024 at 04:38:24PM +0100, Peter Maydell wrote:
> On Thu, 10 Oct 2024 at 18:39, Octavian Purdila <tavip@google.com> wrote:
> >
> > From: Valentin Ghita <valentinghita@google.com>
> >
> > Add option to allow for connecting device GPIOs. This is useful when
> > adding a peripheral device from the command line which uses an
> > interrupt.
> >
> > It takes the following options:
> >
> > * in-dev-path, out-dev-path - required, the device canonical object
> >   path (e.g. /machine/peripheral-anon/device[0],
> >   /machine/iotkit/cluster0/armv7m0) for the devices that should have
> >   their in <-> out GPIOs connected
> >
> > * in-gpio-name, out-gpio-name - optional, the name of the GPIO list;
> >   if not specified, the unnamed GPIO list is used
> >
> > * in-gpio-index, out-gpio-index - optional, the index in the GPIO list
> >   that identifies the GPIO to be used; if not specified 0 (the first
> >   GPIO in the list) is used
> >
> > Usage example:
> >
> >  # add the tmp105 sensor and connects its irq line to the CPU
> >  qemu-system-arm \
> >   --machine mps2-an505 \
> >   --device tmp105,bus=/versatile_i2c/i2c,address=0x50 \
> >   --connect-gpios out-dev-path=/machine/peripheral-anon/device[0],\
> >     in-dev-path=/machine/iotkit/cluster0/armv7m0,in-gpio-index=100
> 
> 
> This seems to be moving down the path towards "create and
> wire up machines on the command line". We shouldn't
> be doing that ad-hoc with one small commandline option
> at a time, we should be doing it with a coherent plan.

Yeah, as a general rule, adding new CLI args is pretty undesirable.
To avoid that we could utilize QOM for representing data:
eg a "gpio-connection" object:

  --object gpio-connection,out-dev-path=/machine/peripheral-anon/device[0],\
           in-dev-path=/machine/iotkit/cluster0/armv7m0,in-gpio-index=100

this would be OK if we're fine with some code somewhere that iterates
over the 'gpio-connection' object instances performing the wiring.

If we want this wiring done in the machine realization path though,
we would want to properties directly assocaited with the devices,
rather than via a side-loaded object.

With regards,
Daniel
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