Re: [RFC PATCH] target/arm: update the cortex-a15 MIDR to latest rev

[Anders Roxell <anders.roxell@linaro.org>]

On Tue, 6 Sept 2022 at 19:23, Alex Bennée <alex.bennee@linaro.org> wrote:
>
> QEMU doesn't model micro-architectural details which includes most
> chip errata. The ARM_ERRATA_798181 work around in the Linux
> kernel (see erratum_a15_798181_init) currently detects QEMU's
> cortex-a15 as broken and triggers additional expensive TLB flushes as
> a result.
>
> Change the MIDR to report what the latest silicon would (r4p0) as well
> as setting the IMPDEF revidr bit to indicate these flushes are not
> needed. This cuts about 5s from my Debian kernel boot with the latest
> 6.0rc1 kernel (29s->24s).
>
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> Cc: Arnd Bergmann <arnd@linaro.org>
> Cc: Anders Roxell <anders.roxell@linaro.org>

Tested-by: Anders Roxell <anders.roxell@linaro.org>

> ---
>  target/arm/cpu_tcg.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/target/arm/cpu_tcg.c b/target/arm/cpu_tcg.c
> index 3099b38e32..59d5278868 100644
> --- a/target/arm/cpu_tcg.c
> +++ b/target/arm/cpu_tcg.c
> @@ -588,7 +588,9 @@ static void cortex_a15_initfn(Object *obj)
>      set_feature(&cpu->env, ARM_FEATURE_EL3);
>      set_feature(&cpu->env, ARM_FEATURE_PMU);
>      cpu->kvm_target = QEMU_KVM_ARM_TARGET_CORTEX_A15;
> -    cpu->midr = 0x412fc0f1;
> +    /* r4p0 cpu, not requiring expensive tlb flush errata */
> +    cpu->midr = 0x414fc0f0;
> +    cpu->revidr = 0x200;
>      cpu->reset_fpsid = 0x410430f0;
>      cpu->isar.mvfr0 = 0x10110222;
>      cpu->isar.mvfr1 = 0x11111111;
> --
> 2.34.1
>