How acpi_walk_resources() find specific _CRS for one device

Experts

I am reading the PCI enumeration code on x86. One thing on ACPI namespace puzzles me.

In the initialize process, the call flow is like this acpi_pci_root_add()
try_get_root_bridge_busnr()
acpi_walk_resources(handle, METHOD_NAME__CRS,
get_root_bridge_busnr_callback, res)

By reading the ACPI spec, this is trying to go through the namespace and find the _CRS method/object.

1. Hmm... I want to know this function is trying to go through the whole namespace or just the device related namespace?
2. If it is searching the whole namespace, how could this function find the device specific resource just by given the "_CRS" as a parameter?
3. Also, if it just go through the device specific namespace, which parameter identify this.

Here is an example in the ACPI specification in 9.11.1:
Device (PCI0) { // PCI Root Bridge

	Name (_HID, EISAID("PNP0A03"))
	Name (_UID, 0)
	Name (_BBN, 0x00)
	Name (_SEG, 0x00) // assign segment 0 of module device to PCI0
	Name (_CRS, ResourceTemplate () {
		WordBusNumber (
			ResourceProducer,
			MinFixed, // _MIF
			MaxFixed,, // _MAF
			0x00, // _GRA
			0x00, // _MIN
			0xFF, // _MAX
			0x0, // _TRA
			0x80) // _LEN
		WordIO (
			ResourceProducer,
			MinFixed, // _MIF
			MaxFixed,,, // _MAF
			0x0000, // _GRA
			0x0000, // _MIN
			0x0CF7, // _MAX
			0x0, // _TRA
			0x0CF8) // _LEN
		DWordMemory (
			ResourceProducer,,
			MinNotFixed, // _MIF
			MaxNotFixed, // _MAF
			NonCacheable, // _MEM
			ReadWrite, // _RW
			0x0FFFFFFF, // _GRA
			0x40000000, // _MIN
			0x5FFFFFFF, // _MAX
			0x0, // _TRA
			0x00000000) // _LEN
	})
	}
}

Device (PCI1) { // PCI Root Bridge

	Name (_HID, EISAID("PNP0A03"))
	Name (_UID, 0)
	Name (_BBN, 0x00)
	Name (_SEG, 0x01) // assign segment 1 of module device to PCI1
	Name (_CRS, ResourceTemplate () {
		WordBusNumber (
			ResourceProducer,
			MinFixed, //
			MaxFixed,, //
			0x00, //
			0x00, //
			0x7F, //
			0x0, //
			0x80) //
		WordIO (
			ResourceProducer,
			MinFixed, //
			MaxFixed, //
			0x0000, //
			0x0D00, //
			0x7FFF, //
			0x0, //
			0x7300) //
		DWordMemory (
			ResourceProducer,
			MinNotFixed,
			MaxNotFixed,
			NonCacheable,
			ReadWrite,
			0x0FFFFFFF,
			0x60000000,
			0x7FFFFFFF,
			0x0,
			0x00000000)
	})
	}
}

We can see there are two PCI Root Bridge, and each has its own _CRS field. And each field has its own busnumber/iores/memios.

So, in the acpi_walk_resources() function, how to find the proper _CRS infomation for a root device?

Richard Yang
Help you, Help me

This piece of code is to invoke ACPI method "_CRS" for "handle", and call get_root_bridge_busnr_callback for each resource descriptor returned by this method.
Here "handle" is the object for the pci root bus or PCI host bridge. "_CRS" is the name of ACPI method, which exists under "handle".

Thanks for your clarification.

I read the acpi code again. And found the namespace tree is created in acpi_scan_init()

{
	...
	result = acpi_bus_scan(ACPI_ROOT_OBJECT, &ops, &acpi_root);
	...
}

And then call the acpi_walk_namespace() to go through the whole namespace. Am I right? And form those handles

I look at the SPEC and code again and find the namespace is loaded by acpi_ns_load_namespace() right?

It will read DSDT/SSDT/PSDT by calling acpi_ns_load_table_by_type.

While I grep the whole source code, but not find the definition of this function.

Richard Yang
Help you, Help me