Re: [PATCH 1/5] acpi: Add basic device probing infrastructure

[Hanjun Guo]

On 09/08/2015 05:57 PM, Marc Zyngier wrote:
> On 07/09/15 22:29, Rafael J. Wysocki wrote:
> > On Friday, September 04, 2015 06:06:48 PM Marc Zyngier wrote:
> > > IRQ controllers and timers are the two types of device the kernel
> > > requires before being able to use the device driver model.
> > >
> > > ACPI so far lacks a proper probing infrastructure similar to the one
> > > we have with DT, where we're able to declare IRQ chips and
> > > clocksources inside the driver code, and let the core code pick it up
> > > and call us back on a match. This leads to all kind of really ugly
> > > hacks all over the arm64 code and even in the ACPI layer.
> > >
> > > In order to allow some basic probing based on the ACPI tables,
> > > introduce "struct acpi_probe_entry" which contains just enough
> > > data and callbacks to match a table, an optional subtable, and
> > > call a probe function. A driver can, at build time, register itself
> > > and expect being called if the right entry exists in the ACPI
> > > table.
> > >
> > > A acpi_probe_device_init() is provided, taking an ACPI table
> > > identifier, and iterating over the registered entries.
> >
> > What about things that are provided by the ACPI namespace (eg. via _MAT) rather
> > than in static tables?
>
> By the time we get to process non-static tables, the whole probing
> infrastructure (including the ACPI interpreter) should be up and
> running. I'm not seeing this stuff as a replacement for more dynamic
> things - quite the opposite. It is only to be used for early bring-up.

Yes, this framework is for static tables and used at boot time,
sometimes quite early, which is before acpi_early_init().

But for _MAT (which is used for dynamic device configuration), it's
really a good question, I think _MAT is mainly for CPU hotplug, and
it's not related to this framework (for GIC init and clock source).
To hot add/remove a whole ARM SoC with _MAT, I think we need more
time to make the spec ready first, that's long term work, and agian
it's nothing to do with this infrastructure if I understand correctly :)

Thanks
Hanjun
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