[Qemu-devel] Re: [PATCH 1/4] prep: Remove bogus BIOS size check

[Andreas Färber]

Am 19.12.2010 um 10:52 schrieb Alexander Graf:

> On 14.12.2010, at 01:49, Andreas Färber wrote:
>
> > r3480 added this check to account for the entry vector 0xfff00100  
> > to be
> > available for CPUs that need it. Today however, the NIP is not yet
> > initialized at this point (zero), so the check always triggers.
> >
> > Cc: Hervé Poussineau <address@hidden>
> > Cc: Alexander Graf <address@hidden>
> > Signed-off-by: Andreas Färber <address@hidden>
> > ---
> > hw/ppc_prep.c |    3 ---
> > 1 files changed, 0 insertions(+), 3 deletions(-)
> >
> > diff --git a/hw/ppc_prep.c b/hw/ppc_prep.c
> > index 1492266..6b22122 100644
> > --- a/hw/ppc_prep.c
> > +++ b/hw/ppc_prep.c
> > @@ -600,9 +600,6 @@ static void ppc_prep_init (ram_addr_t ram_size,
> >    if (filename) {
> >        qemu_free(filename);
> >    }
> > -    if (env->nip < 0xFFF80000 && bios_size < 0x00100000) {
> > -        hw_error("PowerPC 601 / 620 / 970 need a 1MB BIOS\n");
> > -    }
>
> The bios gets mapped to 0xfff00000, so it can at most be 0x100000  
> bytes long which is 1MB. The bogus part of the check is the first,  
> the nip part.

If you look at 2/4, it is checked using BIOS_SIZE define (1024 * 1024)  
further down in the more correct place. :)

At this time - 1/4 - the BIOS gets mapped to 0xffffffff minus BIOS  
size. If the entry is at 0xfffffffc, the BIOS is allowed to be smaller  
than 1 MB. So marking BIOS sizes smaller as 1 MB as error would break  
both the OHW ppc_rom.bin and the IBM 40p BIOS. Therefore it must  
simply go away.

Unless you happen to know a better place for this NIP-dependent check,  
that is. I believe the reset handling was changed at some point?

Andreas