Re: [RFC PATCH v2 10/11] irqchip: mbigen: Add ACPI support

From: Hanjun Guo
Date: Mon Sep 19 2016 - 05:29:05 EST

Hi Marc,

On 2016/9/15 16:49, Marc Zyngier wrote:
On 14/09/16 15:21, Hanjun Guo wrote:
From: Hanjun Guo <hanjun.guo@xxxxxxxxxx>

With the preparation of platform msi support and interrupt producer
in DSDT, we can add mbigen ACPI support now.

We are using _PRS methd to indicate number of irq pins instead
of num_pins in DT.

For mbi-gen,
Device(MBI0) {
Name(_HID, "HISI0152")
Name(_UID, Zero)
Name(_CRS, ResourceTemplate() {
Memory32Fixed(ReadWrite, 0xa0080000, 0x10000)

Name (_PRS, ResourceTemplate() {
Interrupt(ResourceProducer,...) {12,14,....}

Since I know next to nothing about all of this, I'm going to play the
village idiot. What makes it legal to use _PRS as a way to describe the
interrupts that are exposed by MBI0? Looking at the 6.0 spec, I do not
see why the interrupts would be put there instead of _CRS, and why you'd
have a _PRS at all.

_PRS describes possible resource settings for the device, which returns
a list of a device's possible resource settings such as memory range,
interrupt descriptors, and the format of the data in a _PRS object
follows the same format as _CRS object (ACPI 6.1, section 6.2.12),
so Interrupts can be put in the _PRS.

And in ACPI 6.1, section 6.2, it describes the _PRS usage:

"Some resources, however, may be shared amongst several devices. To
describe this, devices that share a resource (resource consumers) must
use the extended resource descriptors (0x7-0xA) described in Section
6.4.3, “Large Resource Data Type.” These descriptors point to a single
device object (resource producer) that claims the shared resource in
its _PRS."

As mbigen is a interrupt producer which provide interrupt resoures
for devices, which matches the usage of _PRS in the spec.

Also, are you going to exhaustively describe all the possible interrupts
via this method? Knowing that the mbigen can expose thousands of
interrupts, I find it slightly mad. Can't you express a range?

Yes, a little bit mad. I can't express a interrupt range in ACPI at
least in current version of spec. But that just adding more lines
of ACPI DSDT code, it's fine to me. or we need to use _DSD to present
similar property "num_pins" in ACPI which I avoid using.