Re: [PATCH v4 0/8] x86: introduce NS16550-compatible UART emulator

["Roger Pau Monné" <roger.pau@citrix.com>]

On Thu, Jul 31, 2025 at 07:21:37PM +0000, dmkhn@proton.me wrote:
> x86 port of Xen lacks vUART facility similar to Arm's vpl011 to support x86
> guest OS bring up in the embedded setups.
> 
> This patch series introduces initial in-hypervisor emulator for
> NS8250/NS16x50-compatible UARTs under CONFIG_VUART_NS16550.
> 
> In parallel domain creation scenario (hyperlaunch), NS16550 emulator helps
> early guest firmware and OS bringup debugging, because it eliminates
> dependency on the external emulator (qemu) being operational by the time
> domains are created.
> 
> The emulator also allows to forward the physical console input to the x86
> domain which is useful when a system has only one physical UART for early
> debugging and this UART is owned by Xen.
> 
> By default, CONFIG_VUART_NS16550 enables emulation of NS16550 at I/O port
> 0x3f8, IRQ#4 in guest OS (legacy COM1). But all legacy COM resources can be
> selected at built-time (no per-domain configuration yet).
> 
> The NS16550 emulator is disabled in default x86 configuration and goes under
> CONFIG_EXPERT in menuconfig.
> 
> Limitations
> ===========
> - Only x86;
> - Only HVM domains support (build-time), PVH domains are not supported yet;

I'm confused by the above statement, HVM domains always have an
emulated serial provided by QEMU if needed, so I think you got this
backwards, and it should instead be:

- Only PVH domains supported, PV and HVM domains are not supported yet.

?

Thanks, Roger.