Re: [Qemu-arm] [Qemu-devel] [PATCH v4 1/5] linux-user: Implement aarch64 PR_SVE_SET/GET_VL

["Alex Bennée" <alex.bennee@linaro.org>]

Peter Maydell <peter.maydell@linaro.org> writes:

> On 6 March 2018 at 12:28, Alex Bennée <alex.bennee@linaro.org> wrote:
>>
>> Richard Henderson <richard.henderson@linaro.org> writes:
>>
>>> As an implementation choice, widening VL has zeroed the
>>> previously inaccessible portion of the sve registers.
>>>
>>> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
>>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>
>>> +                int old_vq = (env->vfp.zcr_el[1] & 0xf) + 1;
>>> +                int vq = MAX(arg2 / 16, 1);
>>> +
>>> +                if (vq < old_vq) {
>>> +                    aarch64_sve_narrow_vq(env, vq);
>>> +                }
>>> +                env->vfp.zcr_el[1] = vq - 1;
>>
>> It seems odd not to have setting this inside cpu64.c. Won't a similar
>> manipulation need to be made for system mode? I'd keep all the logic
>> together in aarch64_sve_narrow_vq (or maybe call it aarch64_sve_set_vq
>> and pass it the current exception level).
>
> I think I asked Richard to put it into linux-user because it was
> in target/arm in an earlier version of this series. The manipulation
> that's happening here is kind of linux-specific (if it were for
> system mode we'd need to think about ZCR_EL2 and ZCR_EL3 as well),
> and the analogy is with cpu_set_tls/cpu_get_tls which are in
> linux-user/arm/target_cpu.h.

Fair enough.

>
> NB: I've already put this series in target-arm.next -- do you want
> me to drop them ? (That would mean they won't go in 2.12, given
> RTH is away.)

No it's fine. We can always fix up minor nits later when system mode is
done.

Acked-by: Alex Bennée <alex.bennee@linaro.org>

>
> thanks
> -- PMM


--
Alex Bennée