Re: [Qemu-devel] [PATCH 0/3] switch to seavgabios

[Anthony Liguori]

On 04/17/2012 09:29 AM, malc wrote:
> On Tue, 17 Apr 2012, Anthony Liguori wrote:
>
> > On 04/17/2012 07:33 AM, malc wrote:
> > > On Tue, 17 Apr 2012, Gerd Hoffmann wrote:
> > >
> > > > On 04/17/12 13:40, malc wrote:
> > > > > On Tue, 17 Apr 2012, Gerd Hoffmann wrote:
> > > > >
> > > > > >     Hi,
> > > > > >
> > > > > > This patch series switches the vgabios binaries shipped by qemu from
> > > > > > the
> > > > > > lgpl'ed vgabios to the seabios version.
> > > > > >
> > > > > > There should be no guest-visible changes (especially no regressions)
> > > > > > in
> > > > > > theory.  The only known (and intentional) exception is the vesa 2.0
> > > > > > protected mode interface which is not implemented by the seavgabios.
> > > > >
> > > > > What's the reason for it not being done?
> > > >
> > > > In summary: Nontrivial effort for questionable gains.
> > >
> > > It worked before, and it should continue to do so. Seabios not having a PM
> > > interface is a regression.
> > >
> > > > First, the lgpl'ed vgabios provides the vesa pmi for the bochs interface
> > > > (-vga std) only, for the cirrus it is not available.
> > >
> > > Well aware, Revision 1.48 has some comments.
> > >
> > > > =>   It can't be a critical feature if our default vga is not supported.
> > >
> > > Opinions are irrelevant, the feature was available before it should
> > > continue to be available.
> >
> > I don't think that's a reasonable position to take.  Do you have a specific
> > workload that uses the pm interface?
>
> Yes, but i need to find time and energy to find out which demos use PM
> window setting.

Okay, it would be very helpful if you could.  I think it's fine to hold off on 
SeaVGABIOS for 1.1 but it would be nice to get it in for 1.2.

Having a specific example of something that needs to not break makes it a whole 
lot easier to deal with IMHO.

> > > > Second, the display panning via vesa pmi was broken in qemu for three
> > > > years(!) and nobody noticed.  The linux kernel's vesafb can use the vesa
> > > > pmi, it is disabled by default though due to bioses tending to be buggy.
> > > >    I'm not aware of other users.
> > > >
> > > > =>   Is this actually used by anyone?  Seems not ...
> > >
> > > It's used by me, when i feel nostalgic and want to watch old DOS stuff.
> >
> > Do you have a specific workload that you know uses the pm interface that you
> > can share?
>
> Do you have a specific reason for asking the same question twice (puzzled)

I don't think it's reasonable to claim something is a regression unless there's 
a real test case that breaks that others can reasonably reproduce.  Hence my 
emphasize on talking about a specific workload over an abstract feature.

Regards,

Anthony Liguori

> > I'd like to confirm that the code actually works today before we try to make
> > it work in a new firmware.
>
> Well, i wrote the patch on which code in LGPL vga bios is based, so yeah,
> it's a pretty safe bet it works.