On Jan 7, 2012 9:31 PM, "Kevin O'Connor" <kevin@koconnor.net> wrote:

On Sat, Jan 07, 2012 at 06:27:06PM +0000, Julian Pidancet wrote:
> On Thu, Jan 5, 2012 at 12:44 AM, Kevin O'Connor <kevin@koconnor.net> wrote:
> >
> > Is the issue that writes to 0x402 are causing an issue on Xen, or just
> > that you don't see the debug output?
> >
> > What's the origin of 0xe9 - is it a "standard" for debug output? What
> > does Xen do today on writes to 0xe9?
> >
>
> Xen has some sort of ring buffer similar to the linux one, that you
> can access using the xl dmesg command. Every guest access to the 0xe9
> port is trapped by the hypervisor which appends the characters to the
> ring buffer. I doubt 0x402 does anything on Xen, aside from beeing
> trapped in qemu if configured correctly, but I havn't tried.

If you really want this, I'm okay with a patch that introduces
CONFIG_DEBUG_PORT, and has Kconfig do all the magic of selecting the
preferred debug port.

That okay?

-Kevin