Re: [PATCH v3 02/12] ppc: Remove stub of PPC970 HID4 implementation

[David Gibson]

On Wed, Feb 19, 2020 at 12:18:34PM +0100, BALATON Zoltan wrote:
> On Wed, 19 Feb 2020, David Gibson wrote:
> > The PowerPC 970 CPU was a cut-down POWER4, which had hypervisor capability.
> > However, it can be (and often was) strapped into "Apple mode", where the
> > hypervisor capabilities were disabled (essentially putting it always in
> > hypervisor mode).
> > 
> > That's actually the only mode of the 970 we support in qemu, and we're
> > unlikely to change that any time soon.  However, we do have a partial
> > implementation of the 970's HID4 register which affects things only
> > relevant for hypervisor mode.
> > 
> > That stub is also really ugly, since it attempts to duplicate the effects
> > of HID4 by re-encoding it into the LPCR register used in newer CPUs, but
> > in a really confusing way.
> > 
> > Just get rid of it.
> > 
> > Signed-off-by: David Gibson <address@hidden>
> > Reviewed-by: Cédric Le Goater <address@hidden>
> > Reviewed-by: Greg Kurz <address@hidden>
> > ---
> > target/ppc/mmu-hash64.c         | 28 +---------------------------
> > target/ppc/translate_init.inc.c | 17 ++++++-----------
> > 2 files changed, 7 insertions(+), 38 deletions(-)
> > 
> > diff --git a/target/ppc/mmu-hash64.c b/target/ppc/mmu-hash64.c
> > index da8966ccf5..a881876647 100644
> > --- a/target/ppc/mmu-hash64.c
> > +++ b/target/ppc/mmu-hash64.c
> > @@ -1091,33 +1091,6 @@ void ppc_store_lpcr(PowerPCCPU *cpu, target_ulong 
> > val)
> > 
> >     /* Filter out bits */
> >     switch (env->mmu_model) {
> > -    case POWERPC_MMU_64B: /* 970 */
> > -        if (val & 0x40) {
> > -            lpcr |= LPCR_LPES0;
> > -        }
> > -        if (val & 0x8000000000000000ull) {
> > -            lpcr |= LPCR_LPES1;
> > -        }
> > -        if (val & 0x20) {
> > -            lpcr |= (0x4ull << LPCR_RMLS_SHIFT);
> > -        }
> > -        if (val & 0x4000000000000000ull) {
> > -            lpcr |= (0x2ull << LPCR_RMLS_SHIFT);
> > -        }
> > -        if (val & 0x2000000000000000ull) {
> > -            lpcr |= (0x1ull << LPCR_RMLS_SHIFT);
> > -        }
> > -        env->spr[SPR_RMOR] = ((lpcr >> 41) & 0xffffull) << 26;
> > -
> > -        /*
> > -         * XXX We could also write LPID from HID4 here
> > -         * but since we don't tag any translation on it
> > -         * it doesn't actually matter
> > -         *
> > -         * XXX For proper emulation of 970 we also need
> > -         * to dig HRMOR out of HID5
> > -         */
> > -        break;
> >     case POWERPC_MMU_2_03: /* P5p */
> >         lpcr = val & (LPCR_RMLS | LPCR_ILE |
> >                       LPCR_LPES0 | LPCR_LPES1 |
> > @@ -1154,6 +1127,7 @@ void ppc_store_lpcr(PowerPCCPU *cpu, target_ulong val)
> >         }
> >         break;
> >     default:
> > +        g_assert_not_reached();
> >         ;
> 
> Is this empty statement (lone semicolon) still needed now that you've added
> something to this case? Thought it was only there to be able to add a label
> to it so it could be removed now. (Does this count as a double ; that a
> recent patch was trying to fix?)

The ; is redundant, but given this whole chunk of code is removed
later in the series, I don't think it's worth messing with.

> 
> Regards,
> BALATON Zoltan
> 
> >     }
> >     env->spr[SPR_LPCR] = lpcr;
> > diff --git a/target/ppc/translate_init.inc.c 
> > b/target/ppc/translate_init.inc.c
> > index a0d0eaabf2..d7d4f012b8 100644
> > --- a/target/ppc/translate_init.inc.c
> > +++ b/target/ppc/translate_init.inc.c
> > @@ -7895,25 +7895,20 @@ static void spr_write_lpcr(DisasContext *ctx, int 
> > sprn, int gprn)
> > {
> >     gen_helper_store_lpcr(cpu_env, cpu_gpr[gprn]);
> > }
> > -
> > -static void spr_write_970_hid4(DisasContext *ctx, int sprn, int gprn)
> > -{
> > -#if defined(TARGET_PPC64)
> > -    spr_write_generic(ctx, sprn, gprn);
> > -    gen_helper_store_lpcr(cpu_env, cpu_gpr[gprn]);
> > -#endif
> > -}
> > -
> > #endif /* !defined(CONFIG_USER_ONLY) */
> > 
> > static void gen_spr_970_lpar(CPUPPCState *env)
> > {
> > #if !defined(CONFIG_USER_ONLY)
> >     /* Logical partitionning */
> > -    /* PPC970: HID4 is effectively the LPCR */
> > +    /* PPC970: HID4 covers things later controlled by the LPCR and
> > +     * RMOR in later CPUs, but with a different encoding.  We only
> > +     * support the 970 in "Apple mode" which has all hypervisor
> > +     * facilities disabled by strapping, so we can basically just
> > +     * ignore it */
> >     spr_register(env, SPR_970_HID4, "HID4",
> >                  SPR_NOACCESS, SPR_NOACCESS,
> > -                 &spr_read_generic, &spr_write_970_hid4,
> > +                 &spr_read_generic, &spr_write_generic,
> >                  0x00000000);
> > #endif
> > }
> > 


-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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