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SubjectRe: ACPI vs Device Tree - moving forward
On Wed, Aug 21, 2013 at 05:57:07PM +0200, Linus Walleij wrote:

> - The I2C address is specified in "reg" - maybe ACPI have
> some other way to assign I2C addresses to I2C devices?
> In any case, it *must* reference the parent I2C controller,
> here that is done implicitly by placing this DT node inside
> the I2C controllers DT node.

That's fine. You put the child device inside the I2C contorller's scope,
which can be done from a separate ACPI table if you want. The address
can be provided via _ADR().

> - Then it is using a GPIO line as interrupt, and specify that
> this shall be configured as a falling edge IRQ.

ACPI 5 permits this.

> - It then tells the interrupt controller parent. So it needs
> to have a reference to whatever interrupt chip device
> will handle that IRQ.

By interrupt controller, do you mean the GPIO controller? ACPI GPIO
definitions include the parent device.

> - Further it *is* an interrupt controller, so devices connected
> to the GPIO lines may generate IRQs and then this
> device should service them. Is it possible that the devices
> connected to this expander in turn use ACPI to describe
> themselves? Then we need a reference in the other
> direction.

I think that's also doable.

> - Further it is a wakeup source, so each IRQ it provides
> on its GPIO lines can be set as a wakeup. I wonder how
> this plays with D-states and ACPI.

That's fine. GPIO lines can be described as causing ACPI events and then
that simply referenced as a wakeup event.

> I did present the above as an extreme example, but if we
> start to combine DT and ACPI we have to have that kind of
> hardware in mind. GPIO expanders with IRQs and all are
> maybe rare on desktops and laptops but very common on
> embedded systems.

Yeah, describing complicated device topology isn't really the problem I
think we'll end up facing - it's the wider range of device configuration
data that worries me.

--
Matthew Garrett | mjg59@srcf.ucam.org


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