Re: [alsa-devel] [PATCH v5 09/17] soundwire: intel: remove platform devices and use 'Master Devices' instead

[Pierre-Louis Bossart]

> > > > +		/* let the SoundWire master driver to its probe */
> > > > +		md->driver->probe(md, link);
> > >
> > > So you are invoking driver probe here.. That is typically role of driver
> > > core to do that.. If we need that, make driver core do that for you!
> > >
> > > That reminds me I am missing match code for master driver...
> >
> > There is no match for the master because it doesn't have an existence in
> > ACPI. There are no _ADR or HID that can be used, the only thing that exists
> > is the Controller which has 4 sublinks. Each master must be added  by hand.
> >
> > Also the SoundWire master cannot be enumerated or matched against a
> > SoundWire bus, since it controls the bus itself (that would be a chicken and
> > egg problem). The SoundWire master would need to be matched on a parent bus
> > (which does not exist for Intel) since the hardware is embedded in a larger
> > audio cluster that's visible on PCI only.
> >
> > Currently for Intel platforms, the SoundWire master device is created by the
> > SOF driver (via the abstraction in intel_init.c).
>
> That is okay for me, the thing that is bit confusing is having a probe
> etc and no match.. (more below)..
>
> > > So we seem to be somewhere is middle wrt driver probing here! IIUC this
> > > is not a full master driver, thats okay, but then it is not
> > > completely transparent either...
> > >
> > > I was somehow thinking that the driver will continue to be
> > > 'platform/acpi/of' driver and master device abstraction will be
> > > handled in the core (for example see how the busses like i2c handle
> > > this). The master device is created and used to represent but driver
> > > probing etc is not done
> >
> > I2C controllers are typically PCI devices or have some sort of ACPI
> > description. This is not the case for SoundWire masters on Intel platforms,
>
> Well the world is not PCI/ACPI... We have controllers which are DT
> described and work in same manner as a PCI device.
Both DT and PCI would use a DIFFERENT matching on the parent bus, not a 
matching provided by the SoundWire subsystem itself.

> > so even if I wanted to I would have no ability to implement any matching or
> > parent bus registration.
> >
> > Also the notion of 'probe' does not necessarily mean that the device is
> > attached to a bus, we use DAI 'drivers' in ASoC and still have probe/remove
> > callbacks.
>
> The "big" difference is that probe is called by core (asoc) and not by
> driver onto themselves.. IMO that needs to go away.

What I did is not different from what existed already with platform 
devices. They were manually created, weren't they?

> > And if you look at the definitions, we added additional callbacks since
> > probe/remove are not enough to deal with hardware restrictions:
> >
> > For Intel platforms, we have a startup() callback which is only invoked once
> > the DSP is powered and the rails stable. Likewise we added an
> > 'autonomous_clock_stop()' callback which will be needed when the Linux
> > driver hands-over control of the hardware to the DSP firmware, e.g. to deal
> > with in-band wakes in D0i3.
> >
> > FWIW, the implementation here follows what was suggested for Greybus 'Host
> > Devices' [1] [2], so it's not like I am creating any sort of dangerous
> > precedent.
> >
> > [1]
> > https://elixir.bootlin.com/linux/latest/source/drivers/greybus/es2.c#L1275
> > [2] https://elixir.bootlin.com/linux/latest/source/drivers/greybus/hd.c#L124
>
> And if you look closely all this work is done by core not by drivers!
> Drivers _should_ never do all this, it is the job of core to do that for
> you.

Please look at the code again, you have a USB probe that will manually 
call the GreyBus device creation.

static int ap_probe(struct usb_interface *interface,
		    const struct usb_device_id *id)
{
	hd = gb_hd_create(&es2_driver, &udev->dev, 	


static struct usb_driver es2_ap_driver = {
	.name =		"es2_ap_driver",
	.probe =	ap_probe, <<< code above
	.disconnect =	ap_disconnect,
	.id_table =	id_table,
	.soft_unbind =	1,
};

The master device probe suggested here is also called as part of the 
parent SOF PCI device probe, same as this USB example. I really don't 
see what your objection is, given that there is no way to deal with the 
SoundWire controller as a independent entity for Intel platforms.