[SeaBIOS] [PATCH 3/6] paravirt: read QEMU_CFG_NOGRAPHIC, store in etc/sercon-enable romfile

[Kevin O'Connor]

On Mon, Sep 11, 2017 at 12:17:04PM +0200, Gerd Hoffmann wrote:
>   Hi,
> 
> > > +    qemu_romfile_add("etc/sercon-enable", QEMU_CFG_NOGRAPHIC, 0,
> > > 2);
> > 
> > Instead of looking at QEMU_CFG_NOGRAPHIC, I think the C code could
> > check if GET_IVT(0x10).segoff == FUNC16(entry_10).segoff .
> 
> It's not that simple.  We need some way to explicitly enable it,
> especially in case a vgabios *is* present (aka aplitmode).  And this is
> what we've agreed on a few months back, IIRC because we don't have to
> extend fw_cfg that way.

Okay.

Separately, how will sercon get the serial port that it is to use?

Looking closer at patch 4 I see:

+    u16 addr = PORT_SERIAL1;
+    SET_LOW(sercon_port, addr);

Is the plan to pull this from a romfile so that it can be set on
coreboot?  If so, perhaps that functionality could be merged with
"etc/sercon-enable" so that coreboot users need only set one cbfs
file.

> Independent from that we have the question what to do by default in
> case no vgabios is present.  IIRC by initial patch set did enable
> sercon in that case, but I changed it after some discussions.
> 
> Don't remember what the reason was though.  Cc'ing Daniel + Paolo

Okay.  It would be nice to have the correct responses to 1000, 1002,
1003, and 100f even if serial output wasn't desired.

-Kevin