On Sat, Apr 6, 2019 at 10:32 AM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > Well, at least that's forward progress. I don't know what pstore is or > what connection it has to the USB subsystem. Does the machine hang > similarly if you boot without the Comtrol PCI card present? Yes the box boots fine when the Comtrol PCI card is *not* present. > For that matter, what happens if you remove EHCI from the kernel > configuration completely? If I remove USB support, the box still hangs after registering the pstore, but if I remove pstore support and APEI support from the kernel then the box boots without issue. > As for how the PCI card affects the USB handoff, it depends on how the > BIOS behaves. Normally the BIOS will take control of all the available > EHCI controllers during bootup (so that it can use them to communicate > with a USB keyboard or mouse), including controllers on add-on PCI > cards as well as those on the motherboard. When the kernel starts up, > it tries to take ownership of the controllers away from the BIOS > (that's the handoff) so that Linux can use them. However, if the BIOS > was never tested for handoff of USB controllers on add-on PCI cards, it > could easily have a bug that would crash the machine. The Comtrol card provides 32 serial ports, via a breakout box, but it has no USB functionality, which was why I was surprised that its presence somehow breaks the USB hand off.
