Re: [OpenBIOS] Re: [RFC PATCH 0/2] QEMU/openbios: PPC Software TLB support in the G4 family

[Cédric Le Goater]

On 11/26/21 13:13, Fabiano Rosas wrote:
> Segher Boessenkool <segher@kernel.crashing.org> writes:
>
> > Hi!
> >
> > On Fri, Nov 26, 2021 at 09:34:44AM +0100, Cédric Le Goater wrote:
> > > On 11/25/21 10:38, Segher Boessenkool wrote:
> > > > On Thu, Nov 25, 2021 at 01:45:00AM +0100, BALATON Zoltan wrote:
> > > > > As for guests, those running on the said PowerMac G4 should have support
> > > > > for these CPUs so maybe you can try some Mac OS X versions (or maybe
> > > >
> > > > OSX uses hardware pagetables.
> > > >
> > > > > MorphOS but that is not the best for debugging as there's no source
> > > > > available nor any help from its owners but just to see if it boots it may
> > > > > be sufficient, it should work on real PowerMac G4).
> > > >
> > > > I have no idea what MorphOS uses, but I bet HPT as well.  That is
> > > > because HPT is fastest in general.  Software TLB reloads are good in
> > > > special cases only; the most common is real-time OSes, which can use its
> > > > lower guaranteed latency for some special address spaces (and can have a
> > > > simpler address map in general).
> > >
> > > The support was added to QEMU knowing that Linux didn't handle soft TLBs.
> > > And the commit says that it was kept disabled initially. I guess that was
> > > broken these last years.
> >
> > Ah :-)  So when was it enabled, do you know?
>
> Hm.. That commit message does not match the code. They simply added the
> software TLB implementation to an already existing SOFT_74xx MMU
> model. I don't see anything that would keep it disabled at that time.

because most of the cpu definitions in ppc_defs[] are protected by a :

#if defined (TODO)

See below. commit 8ca3f6c3824c ("Allow selection of all defined PowerPC
74xx (aka G4) CPUs.") removed the TODO without a reason :/ This is old,
when SVN was in used.


Thanks,

C.

....
#if defined (TODO)
    /* PowerPC 7450 (G4)                                                     */
    POWERPC_DEF("7450",        CPU_POWERPC_7450,        0xFFFFFFFF, 7450),
    /* Code name for PowerPC 7450                                            */
    POWERPC_DEF("Vger",        CPU_POWERPC_7450,        0xFFFFFFFF, 7450),
#endif
#if defined (TODO)
    /* PowerPC 7450 v1.0 (G4)                                                */
    POWERPC_DEF("7450v1.0",    CPU_POWERPC_7450_v10,    0xFFFFFFFF, 7450),
#endif
#if defined (TODO)
    /* PowerPC 7450 v1.1 (G4)                                                */
    POWERPC_DEF("7450v1.1",    CPU_POWERPC_7450_v11,    0xFFFFFFFF, 7450),
#endif
#if defined (TODO)
    /* PowerPC 7450 v1.2 (G4)                                                */
    POWERPC_DEF("7450v1.2",    CPU_POWERPC_7450_v12,    0xFFFFFFFF, 7450),
#endif
#if defined (TODO)
    /* PowerPC 7450 v2.0 (G4)                                                */
    POWERPC_DEF("7450v2.0",    CPU_POWERPC_7450_v20,    0xFFFFFFFF, 7450),
#endif
#if defined (TODO)
    /* PowerPC 7450 v2.1 (G4)                                                */
    POWERPC_DEF("7450v2.1",    CPU_POWERPC_7450_v21,    0xFFFFFFFF, 7450),
#endif
#if defined (TODO)
    /* PowerPC 7441 (G4)                                                     */
    POWERPC_DEF("7441",        CPU_POWERPC_74x1,        0xFFFFFFFF, 7440),
    /* PowerPC 7451 (G4)                                                     */
....