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Message-ID: <CANSNSoVpnK6fyfFct7cLNRJAvdLWh0ac=isnPOkOAp4LV+WoSw@mail.gmail.com> Date: Mon, 15 Apr 2019 16:47:06 -0500 From: Jesse Hathaway <jesse@...ki-mvuki.org> To: Alan Stern <stern@...land.harvard.edu> Cc: Bjorn Helgaas <helgaas@...nel.org>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, Mathias Nyman <mathias.nyman@...el.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, linux-usb@...r.kernel.org Subject: Re: Regression causes a hang on boot with a Comtrol PCI card On Sat, Apr 6, 2019 at 10:32 AM Alan Stern <stern@...land.harvard.edu> 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.
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