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

[Ben Guthro <ben@xxxxxxxxxx>]

On Thu, Jan 17, 2013 at 11:09 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>> 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).
>
> Jan

I'm dragging this thread back up from the archives, because I think it is still
applicable, and now that some of the other S3 scheduling things are explained,
this is a good fix.

My assertion in this thread about getting into this loop when no
serial is in use
turned out to be false.

However, if you are using serial with one of these SuperIO controllers on the
LPC bus, you will get into an infinite loop at resume time.

Ben

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