Re: [RFC PATCH 00/16] Refine PCI host bridge scan interfaces

From: Tomasz Nowicki
Date: Thu Nov 20 2014 - 07:01:19 EST

On 18.11.2014 13:27, Arnd Bergmann wrote:
On Tuesday 18 November 2014 20:17:57 Yijing Wang wrote:

I hope platforms with ACPI or DT could both use pci_create_host_bridge().
Why we need to use two different ways to process it ?

These are completely different use cases:

a) For DT, we want loadable device drivers that start by probing a host
bridge device which was added through the DT platform code. The
driver is self-contained, and eventually we want to be able to unload
it. We have lots of different per-soc drivers that require different

b) For ACPI, the interface is defined in the ACPI spec across architectures
and SoCs, we don't have host bridge drivers and the code that initializes
the PCI is required early during boot and called from architecture
code. There is no parent device, as ACPI sees PCI as a fundamental building
block by itself, and there are no drivers because the firmware does
the initial hardware setup, so we only have to access the config space.

Hmmm, I'm a little confused, so why you think ACPI host driver should not use
pci_create_host_bridge(), because ACPI PCI driver has no parent device ?

It's one of the difference. Having a parent device can certainly make your
life simpler, since you have devm_kzalloc(), dev_info(), etc. Coming from
the other end, I think ACPI needs PCI to be available during early boot,
at a time where we might not want pci_create_host_bridge() to do the
right thing.

Device pointer is not required for ACPI, struct acpi_device is all we need to get all that info. If pci_create_host_bridge() would be DT specific, it would be nice to have sth similar for ACPI but that is out of this patch set scope.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at