The PCI IDE Programming Interface byte (PCI spec §3.1.1) encodes
per-channel mode: bit 0 = primary native, bit 2 = secondary native.
The previous code panicked on native-mode channels and also had a
bug checking bit 0 for both channels (secondary should check bit 2).
Native mode now reads I/O and control bases from PCI BARs (BAR0/1 for
primary, BAR2/3 for secondary) instead of hardcoded legacy ports.
Interrupt line comes from legacy_interrupt_line when available.
Red Bear OS
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