Re: [PATCH 01/13] target/arm: Use new CBAR encoding for all v8 CPUs, not all aarch64 CPUs

[Richard Henderson]

On 2/6/24 23:29, Peter Maydell wrote:
> We support two different encodings for the AArch32 IMPDEF
> CBAR register -- older cores like the Cortex A9, A7, A15
> have this at 4, c15, c0, 0; newer cores like the
> Cortex A35, A53, A57 and A72 have it at 1 c15 c0 0.
>
> When we implemented this we picked which encoding to
> use based on whether the CPU set ARM_FEATURE_AARCH64.
> However this isn't right for three cases:
>   * the qemu-system-arm 'max' CPU, which is supposed to be
>     a variant on a Cortex-A57; it ought to use the same
>     encoding the A57 does and which the AArch64 'max'
>     exposes to AArch32 guest code
>   * the Cortex-R52, which is AArch32-only but has the CBAR
>     at the newer encoding (and where we incorrectly are
>     not yet setting ARM_FEATURE_CBAR_RO anyway)
>   * any possible future support for other v8 AArch32
>     only CPUs, or for supporting "boot the CPU into
>     AArch32 mode" on our existing cores like the A57 etc
>
> Make the decision of the encoding be based on whether
> the CPU implements the ARM_FEATURE_V8 flag instead.
>
> This changes the behaviour only for the qemu-system-arm
> '-cpu max'. We don't expect anybody to be relying on the
> old behaviour because:
>   * it's not what the real hardware Cortex-A57 does
>     (and that's what our ID register claims we are)

Not even that, because max resets MIDR.

Anyway,
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~