Re: [PATCH RFC 02/11] ACPI: Introduce irq_get() for static fwnodes

[Lorenzo Pieralisi <lpieralisi@kernel.org>]

On Wed, Oct 21, 2026 at 09:58:33AM +0300, Andy Shevchenko wrote:
> On Tue, Oct 20, 2026 at 05:30:00PM +0200, Lorenzo Pieralisi wrote:
> > On Mon, Oct 19, 2026 at 08:05:50PM +0200, Rafael J. Wysocki (Intel) wrote:
> > > On Mon, Oct 19, 2026 at 12:34 PM Lorenzo Pieralisi
> > > <lpieralisi@kernel.org> wrote:
> 
> [...]
> 
> > > Basically, yes, the idea is to defer the creation of the platform
> > > device until the dependency is met.
> > > 
> > > > till the dependencies are cleared but then, without a _CRS, where will
> > > > the consumer driver find the platform device resources ?
> > > 
> > > Well, good question.
> > > 
> > > > There are multiple facets in this issue and possibly some of them have
> > > > been already solved but I need to pull them together.
> > > >
> > > > > Note that the dependencies can be added to acpi_dep_list after
> > > > > creating a struct acpi_device with acpi_add_single_object() and
> > > > > acpi_scan_add_dep() is not really suitable for that, but it should be
> > > > > doable if the dependencies can be found.
> > > > >
> > > > > > I need to have a deeper look into this next week but I wanted to ask first
> > > > > > whether there was something I missed - most likely.
> > > > >
> > > > > Well, it is not really straightforward.
> > > >
> > > > Yes it is getting messy. This RFC, with all its flaws, does not transparently
> > > > prevents enumeration but rather relies on -EPROBE_DEFER to sort out
> > > > dependencies - though it does so by adding more stuff into ACPI static fwnode
> > > > that to be honest I'd rather see gone.
> > > 
> > > I think what you need is a notification mechanism that will trigger
> > > when a specific device (enumerated via the ACPI Namespace) becomes
> > > operational.  It doesn't look like any of the existing ones (platform
> > > device probe deferral or ACPI device dependencies tracking) is really
> > > suitable for your use case.
> > 
> > Yes. It might just be a notification from ACPI core to say "the driver for
> > this ACPI device probed, go create platform devices that depends on it".
> > 
> > We can check and track the dependency in code that does create those
> > devices today.
> > 
> > I will think about this to see how bad this might look like.
> 
> Don't we do something similar in drivers/acpi/x86/lpss.c?

I suppose I can add a notifier that checks whether the device whose
companion represents the ACPI device a given platform device IRQ depends
on was bound to its driver and then map the IRQ and add the platform device
_then_ - after all that's what acpi_dev_clear_dependencies() does (similar
at least).

There is still the question - where the GSI number, flags should be
stashed so that the notifier can grab them in a uniform way. We
could simply attach platform data storing those values to a pdev, either on
a per static table basis or generalize the data so that a single notifier
would be able to deal with it.

That or I can just piggyback on acpi_dev_clear_dependencies() and add
a separate dep mechanism to acpi_dep_data that instead of being acpi_handle
based the consumer is fwnode based (something Rafael mentioned before).

I will have a stab at this and see what's the least bad solution I can
come up with.

I suppose we are scrapping the -EPROBE_DEFER solution (ie this set),
what we are talking about above won't need to defer anything other
than the time when platform devices are added.

Thanks,
Lorenzo