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target/ppc: Remove the software TLB model of 7450 CPUs

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(Applies to 7441, 7445, 7450, 7451, 7455, 7457, 7447, 7447a and 7448)

The QEMU-side software TLB implementation for the 7450 family of CPUs
is being removed due to lack of known users in the real world. The
last users in the code were removed by the two previous commits.

A brief history:

The feature was added in QEMU by commit 7dbe11acd8 ("Handle all MMU
models in switches...") with the mention that Linux was not able to
handle the TLB miss interrupts and the MMU model would be kept
disabled.

At some point later, commit 8ca3f6c382 ("Allow selection of all
defined PowerPC 74xx (aka G4) CPUs.") enabled the model for the 7450
family without further justification.

We have since the year 2011 [1] been unable to run OpenBIOS in the
7450s and have not heard of any other software that is used with those
CPUs in QEMU. Attempts were made to find a guest OS that implemented
the TLB miss handlers and none were found among Linux 5.15, FreeBSD 13,
MacOS9, MacOSX and MorphOS 3.15.

All CPUs that registered this feature were moved to an MMU model that
replaces the software TLB with a QEMU hardware TLB
implementation. They can now run the same software as the 7400 CPUs,
including the OSes mentioned above.

References:

- https://bugs.launchpad.net/qemu/+bug/812398
  https://gitlab.com/qemu-project/qemu/-/issues/86

- https://lists.nongnu.org/archive/html/qemu-ppc/2021-11/msg00289.html
  message id: 20211119134431.406753-1-farosas@linux.ibm.com

Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20211130230123.781844-4-farosas@linux.ibm.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
This commit is contained in:
Fabiano Rosas 2021-12-17 17:57:16 +01:00 • committed by Cédric Le Goater
parent b137fb72d7
commit a09410ed1f
8 changed files with 6 additions and 137 deletions
Download patch file Download diff file Expand all files Collapse all files

26
target/ppc/cpu_init.c
View file

@ -945,31 +945,6 @@ static void register_l3_ctrl(CPUPPCState *env)
0x00000000);
}
static void register_74xx_soft_tlb(CPUPPCState *env, int nb_tlbs, int nb_ways)
{
#if !defined(CONFIG_USER_ONLY)
env->nb_tlb = nb_tlbs;
env->nb_ways = nb_ways;
env->id_tlbs = 1;
env->tlb_type = TLB_6XX;
/* XXX : not implemented */
spr_register(env, SPR_PTEHI, "PTEHI",
SPR_NOACCESS, SPR_NOACCESS,
&spr_read_generic, &spr_write_generic,
0x00000000);
/* XXX : not implemented */
spr_register(env, SPR_PTELO, "PTELO",
SPR_NOACCESS, SPR_NOACCESS,
&spr_read_generic, &spr_write_generic,
0x00000000);
/* XXX : not implemented */
spr_register(env, SPR_TLBMISS, "TLBMISS",
SPR_NOACCESS, SPR_NOACCESS,
&spr_read_generic, &spr_write_generic,
0x00000000);
#endif
}
static void register_usprg3_sprs(CPUPPCState *env)
{
spr_register(env, SPR_USPRG3, "USPRG3",
@ -9238,7 +9213,6 @@ void ppc_cpu_dump_state(CPUState *cs, FILE *f, int flags)
case POWERPC_MMU_32B:
case POWERPC_MMU_601:
case POWERPC_MMU_SOFT_6xx:
case POWERPC_MMU_SOFT_74xx:
#if defined(TARGET_PPC64)
case POWERPC_MMU_64B:
case POWERPC_MMU_2_03: