Re: [Xen-devel] ehci dbgp reset during boot?

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.06.13 at 15:18, Ben Guthro <ben@xxxxxxxxxx> wrote:
> I'm seeing an issue with the EHCI debug port functionality, that I'm
> wondering whether it is a known limitation of the hardware, or if this
> is a bug.
> 
> On a particular system that I had limited debug capabilities in the
> past (Dell Inspiron 15 i3) I am seeing the debug messages abruptly
> stop during boot, followed by garbage that looks like an uninitialized
> serial port:
> 
> 
> ...
> [    3.816669] Freeing SMP alternatives: 20k freed
> [    3.819784] ACPI: Core revision 20121018
> x~x~P
> 
> 
> This always stops with the same ACPI message.
> I'm wondering if some bus level reset is going on, that might be
> confusing the debug port, and perhaps it is not recovering from this?

Possibly - who knows what firmware does... Does the BIOS setup
have any option to turn off as much of legacy emulation as
possible (which otherwise may get turned off as ACPI gets enabled)?
If so, I'd suggest trying this. If not, only the machine or BIOS
vendors may know what's going on there... The reset that the code
is prepared to deal with happens in any case much later than where
you show output stops, and I never saw any garbage coming
through (albeit there is a certain percentage of cases where
recovery doesn't work, yet according to my testing that's also the
case for the original Linux code).

Jan


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