uefi: Fix broken bridge recursion in PCI enumeration

[seijikun]

The bridge detection to decide whether we want to recurse to a subsequent bus was broken due to two reasons:

• Register struct PciHeader1Register6 had the wrong order, which caused the range (start - end) of subsequent bus numbers to be swapped
• Forgot to mask the header_type with 0b01111111, because the most significant bit specifies whether the device is a multi-function device.

Checklist

• Sensible git history (for example, squash "typo" or "fix" commits). See the Rewriting History guide for help.
• Update the changelog (if necessary)

[phip1611]

Thanks for the fix! Do you see the potential for a integration test?

[seijikun]

Thanks for the fix! Do you see the potential for a integration test?

Yes, but not yet.
First, I would like to add DevicePath generation for every found PCI device.
(That's what this MR works towards)
With those, writing a pci integration tests should be much more robust.

[phip1611]

What is currently the blocker when it comes to device path generation for you? @nicholasbishop created significant groundwork for constructing device paths?

[seijikun]

What is currently the blocker when it comes to device path generation for you? @nicholasbishop created significant groundwork for constructing device paths?

Mostly that it already was 03:00 AM "yesterday".

[seijikun]

Can we do the DevicePath generation and subsequentely the integration test in a separate MR?
I will probably need some support with the DevicePath API.

[seijikun]

Ah, just for the record:
The integration test would not have caught this bug. At no point did the current implementation yield incorrect results.

The broken PCI bridge recursion was compensated for by iterating through all bus numbers of a PciRoot in PciRootBridgeIo::enumerate(). I had mistakenly assumed that this was necessary - until I tried to generate device paths and discovered the broken recursion.