[edk2-devel] [PATCH v2 0/4] Add extra pci roots support for Arm

[Laszlo Ersek]

On 12/15/20 13:52, Jiahui Cen wrote:
> For x86, Linux does not handle the pci resource assignment. But for arm, it
> would assign all the pci resources, unless we explicitly let Linux preserve
> PCI resource alignment made by firmware, using "PCI Boot Configuration"
> _DSM function.

This difference between x86 and arm seems inexplicable to me.

> What do you think of adding "PCI Boot Configuration" _DSM function into
> dsdt table to make kernel use firmware's resource configuration?

The relevant kernel commits seem to be:

- 18e94a338436 ("PCI: Make a shareable UUID for PCI firmware ACPI _DSM",
2015-04-08)

- a78cf9657ba5 ("PCI/ACPI: Evaluate PCI Boot Configuration _DSM",
2019-06-21)

I've also read now section "4.6.5. _DSM for Ignoring PCI Boot
Configurations" in the "PCI(TM) Firmware Specification,
Revision 3.1, December 13, 2010".

Basically if this _DSM#5 function exists, it tells the OS whether it is
required to honor the firmware-assigned resources (value 0), or if it is
free to reassign (value 1). If the function does not exist at all, then,
"the operating system may continue to use the legacy handling regarding
the boot configuration".

Without knowing more, I consider it a bug that aarch64 Linux uses a
default strategy (in the absence of the _DSM#5 function) that is the
opposite of the x86 default. But, you seem to be right that there is a
specified way to convince arm64 Linux otherwise. Can you indeed add this
_DSM#5 function to the "virt" machine's ACPI generator, returning value
0, and see if it makes a difference?

Thanks!
Laszlo



-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#69122): https://edk2.groups.io/g/devel/message/69122
Mute This Topic: https://groups.io/mt/78135572/1813853
Group Owner: devel+owner at edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [edk2-devel-archive at redhat.com]
-=-=-=-=-=-=-=-=-=-=-=-