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Re: [Xen-devel] [PATCH] ns16550: delay resume until dom0 ACPI has a chance to run

>>> On 16.01.13 at 22:48, Ben Guthro <ben@xxxxxxxxxx> wrote:
> On Wed, Jan 16, 2013 at 4:40 PM, Malcolm Crossley
> <malcolm.crossley@xxxxxxxxxx> wrote:
>> Do these laptops (T430/T530) have built in serial?
> They seem to have the hardware for it, but no actual serial connector
> out of the machine.
> This hardware provides the legacy port that Xen initializes in
> xen/arch/x86/setup.c __start_xen()
> When the resume happened, it was getting stuck in __ns16550_poll()
> because it thought that the
> LSR register was 0xFF - and had lots of data to read. It got stuck in
> that while loop, and never
> exited.

So before acking the patch I'd like to understand how we end up
in that loop even when no serial console is in use. Assuming that's
because the post-IRQ initialization (mostly) unconditionally inserts
the timer, that shouldn't be an issue on -unstable (as post-IRQ
init of the individual drivers doesn't get called anymore when no
respective command line option was present, and likewise their
suspend/resume handlers don't get called anymore in that case).
In which case backporting from -unstable would be preferable
over putting custom stuff on the 4.x branches (albeit we likely
still want the change here to have a way to resume with serial
console, but the impact would be quite different).


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