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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.04.13 at 15:51, Ben Guthro <ben@xxxxxxxxxx> wrote:
> 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).
> 
> 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.

Good.

> 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.

Yes, I can see how that can happen.

However, there's another loose end on that thread - see your
response
http://lists.xen.org/archives/html/xen-devel/2013-01/msg01223.html

And I'd expect you to resubmit anyway, in order to
- fix the description (as you had promised to Pasi)
- fix various coding style issues
- Cc Keir (who will have to ack the patch in order for it to go in)
- make sure we're not applying something stale after this long a
  time

Jan


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