Add a PCI driver that follows the Arm DEN0115 spec

[andrew]

Summary

Add a n attachment to the pci_host_generic driver for the Arm DEN0115
PCI Configuration Space Access Firmware Interface [1]. This can be used
when PCI controllers need to implement quirks in the PCI root bus.
To handle this the firmware implements a SMCCC interface the driver can
use to read and write the configuration register.

This has been tested on a Raspberry Pi 4 booting with EDK2.

[1] https://developer.arm.com/documentation/den0115/latest

Sponsored by: Arm Ltd

[markmi_dsl-only.net]

sys/dev/pci/pci_host_generic_den0115.c

87

The comment's reference to >= v1.1 ("at least") vs. the code's check for v1.0 seem mismatched:

. . . ||
(SMCCC_VERSION_MAJOR(smccc_version) == 1 &&
	     SMCCC_VERSION_MINOR(smccc_version) == 0)

[markmi_dsl-only.net]

As a matter of curiosity, did something specific prompt having this form of PCI Configuration Space Access added? FreeBSD has been able to boot the RPi4B's for a long time, even via EDK2. So the test case does not seem to be a driving use case. Are there other known examples of this form of PCI Configuration Space Access needing-to-be/being-able-to-be used?