Re: Using a generic PciHostBridgeDxe driver for a multi-PCIe-domain platform

[Laszlo Ersek <lersek@redhat.com>]

On 05/30/17 20:32, Laszlo Ersek wrote:
> On 05/30/17 18:23, Vladimir Olovyannikov wrote:
>> Hi,
>>
>> I've started PCIe stack implementation design for an armv8 aarch64
>> platform.
>> The platform's PCIe represents several host bridges, and each hostbridge
>> has one rootbridge.
>> They do not share any resources between each other.
>> Looking into the PciHostBridgeDxe implementation I can see that it
>> supports only one hostbridge, and there is a comment:
>> // Most systems in the world including complex servers have only one Host
>> Bridge.
>>
>> So in my case should I create my own PciHostBridgeDxe driver supporting
>> multiple hostbridges and do not use the Industry standard driver?
>> I am very new to it, and will appreciate any help or idea.
> 
> I think you can use PciHostBridgeDxe on this platform:
> 
> - Implement a PciHostBridgeLib instance (see
> <MdeModulePkg/Include/Library/PciHostBridgeLib.h>) that returns
> PCI_ROOT_BRIDGE objects with different Segment fields, from
> PciHostBridgeGetRootBridges().
> 
> - Implement a PciSegmentLib instance (see
> <MdePkg/Include/Library/PciSegmentLib.h>) that routes the config space
> addresses, encoded by the PCI_SEGMENT_LIB_ADDRESS() macro, according to
> your platform.
> 
> PciHostBridgeDxe and PciBusDxe should "just work" atop. To my
> understanding, PciBusDxe delegates all config space accesses to
> PciHostBridgeDxe, via EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL. And
> PciHostBridgeDxe delegates all config space accesses to the platform's
> PciSegmentLib.

A small addition. Assuming the general case, i.e. when you have a
different number of root bridges on each of several host bridges, you
still have to number all those root bridges incrementally, in a curious,
flat address space. And that address space is the PcieRoot(N) device
path node that is supposed to start the "DevicePath" member of each
PCI_ROOT_BRIDGE object that you return from PciHostBridgeGetRootBridges().

You can read about the PcieRoot() devpath node in the UEFI 2.6 spec.
Basically, you have

ACPI_HID_DEVICE_PATH.Header = <fill in as usual>;
ACPI_HID_DEVICE_PATH.HID = EFI_PNP_ID (0x0a08);
ACPI_HID_DEVICE_PATH.UID = <fill in incrementally across host bridges>;

The UID values used in these devpath nodes should preferably match the
UID values of the corresponding PCI Express Root Bridge objects
(=PNP0A08) that you expose in your ACPI tables (DSDT and/or SSDT).

Thanks
Laszlo