Re: [PATCH v2 00/35] Introduce NS8250 UART emulator

[Denis Mukhin <dmkhn@xxxxxxxxx>]

On Monday, December 16th, 2024 at 1:04 AM, Roger Pau Monné 
<roger.pau@xxxxxxxxxx> wrote:

>
>
> On Sat, Dec 14, 2024 at 07:05:15PM +0100, Marek Marczykowski-Górecki wrote:
>
> > On Thu, Dec 05, 2024 at 08:41:30PM -0800, Denis Mukhin via B4 Relay wrote:
> >
> > > The patch series introduces initial in-hypervisor emulator for
> > > NS8250/NS16x50-compatible UARTs under CONFIG_HAS_VUART_NS8250.
> > >
> > > In parallel domain creation scenario (hyperlaunch), NS8520 emulator helps
> > > early guest OS bringup debugging, because it eliminates dependency on the
> > > external emulator being operational by the time domains are created. Also,
> > > there's no early console facility similar to vpl011 to support x86 guest 
> > > OS
> > > bring up.
> > >
> > > The NS8250 emulator is disabled by default.
> >
> > On a high level, why the mechanism used by earlyprintk=xen (IIUC i/o
> > port 0xe9) isn't enough?
> > Hyperlaunch can't start full (Xen-unaware) HVM domains anyway, so
> > a requirement to use a Xen-specific interface for the console shouldn't be
> > an issue, no?
>
>
> I assume the point is to provide a minimal set of non-Xen specific
> interfaces so that a guest could work if made to use only those
> interfaces. The 0xE9 hack is quite common for emergency printing, but
> it doesn't allow for input, which the ns8250 does.

Yes, my major objective was providing a simpler debugging facility under Xen
w/o modifying guest OS software.

>
> Thanks, Roger.