Re: [PATCH 3/3] target/arm: Default to 1GHz cntfrq for 'max' and new CPUs

[Richard Henderson <richard.henderson@linaro.org>]

On 4/19/24 11:46, Peter Maydell wrote:
> In previous versions of the Arm architecture, the frequency of the
> generic timers as reported in CNTFRQ_EL0 could be any IMPDEF value,
> and for QEMU we picked 62.5MHz, giving a timer tick period of 16ns.
> In Armv8.6, the architecture standardized this frequency to 1GHz.
> 
> Because there is no ID register feature field that indicates whether
> a CPU is v8.6 or that it ought to have this counter frequency, we
> implement this by changing our default CNTFRQ value for all CPUs,
> with exceptions for backwards compatibility:
> 
>   * CPU types which we already implement will retain the old
>     default value. None of these are v8.6 CPUs, so this is
>     architecturally OK.
>   * CPUs used in versioned machine types with a version of 9.0
>     or earlier will retain the old default value.
> 
> The upshot is that the only CPU type that changes is 'max'; but any
> new type we add in future (whether v8.6 or not) will also get the new
> 1GHz default.
> 
> It remains the case that the machine model can override the default
> value via the 'cntfrq' QOM property (regardless of the CPU type).
> 
> Signed-off-by: Peter Maydell<peter.maydell@linaro.org>
> ---
>   target/arm/cpu.h       | 11 +++++++++++
>   target/arm/internals.h | 12 ++++++++++--
>   hw/core/machine.c      |  4 +++-
>   target/arm/cpu.c       | 28 ++++++++++++++++++++++------
>   target/arm/cpu64.c     |  2 ++
>   target/arm/tcg/cpu32.c |  4 ++++
>   target/arm/tcg/cpu64.c | 18 ++++++++++++++++++
>   7 files changed, 70 insertions(+), 9 deletions(-)

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

r~