Re: [edk2-devel] [PATCH 0/4] OvmfPkg: add virtio serial driver

["Gerd Hoffmann" <kraxel@redhat.com>]

  Hi,

> > libvirt snippet (add to <devices>):
> > 
> >      <console type='pty'>
> >        <target type='virtio' port='0'/>
> >      </console>
> Was thinking about the motivation to add the virtio serial device.
> 
> AFAIU this can provide a console in bios/early boot based on "virtio".
> Currently we can only get it with emulated PTY device which is slow
> because of frequent VMEXITS because of ioport write?

Yes, it has better performance because it wouldn't vmexit for every
single character.

Dawback is that it wouldn't work for early logging, the driver loads
relatively late because it depends on pci and virtio.  So if the
firmware panics in SEC or PEI you wouldn't see that.

So for debug logging it isn't the best choice, for efi shell and grub it
works fine.

> Or is there any other reason (e.g across the ARCH support) to add this
> support in UEFI ?

Should work on all architectures, although it needs some platform setup
code to have the firmware actually bind the firmware console to it (see
patch #4).

Another nice property of a virtio console is that systemd will spawn a
getty there even if it is not explicitly configured as console device.

take care,
  Gerd