[SeaBIOS] CHS translation (BIOS incompatibility)

[Kevin O'Connor]

On Tue, Jun 05, 2018 at 06:09:54PM +0300, Nikolay Ivanets wrote:
> > As far as I know, QEMU should be able to tell SeaBIOS the exact
> > geometry to use (eg, via qemu -hdachs c,h,s[,t] option).  If you're
> > not getting the expected behavior, be sure to include the seabios log
> > file - see: https://www.seabios.org/Debugging
> >
> 
> Here is geometry when I have with patched bios (Windows boot):
>     drive 0x000f57f0: PCHS=16383/16/63 translation=lba
> LCHS=1024/255/32 s=143305920
> 
> Here is geometry I have with original Seabios (boot fails):
>     drive 0x000f0bd0: PCHS=16383/16/63 translation=lba
> LCHS=1024/255/63 s=143305920
> 
> Qemu limits what we can specify in CHS to 16383, 16 and 63
> respectively and I don't see any combinations which will perform
> necessary translation from PCHS=16383/16/63 to LCHS=1024/255/32.

If I understand it correctly, you're looking for LCHS=1024/255/32.  I
don't know why QEMU wont let you specify heads=255, but short of doing
that, I don't see a way for SeaBIOS to obtain that logical mapping.

The disk geometry translation stuff is arcane - the SeaBIOS code is
translated from the original Bochs bios code.  If it needs to be
enhanced, it would require both a qemu patch (to specify the desired
translation/geometry) and a seabios patch (to implement it).

-Kevin