Re: [PATCH v3 03/15] target/arm: Do not use aarch64_sve_zcr_get_valid_len in reset

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

On 5/31/22 05:15, Peter Maydell wrote:
> On Fri, 27 May 2022 at 19:07, Richard Henderson
> <richard.henderson@linaro.org> wrote:
>>
>> We don't need to constrain the value set in zcr_el[1],
>> because it will be done by sve_zcr_len_for_el.
>>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>   target/arm/cpu.c | 3 +--
>>   1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
>> index d2bd74c2ed..0621944167 100644
>> --- a/target/arm/cpu.c
>> +++ b/target/arm/cpu.c
>> @@ -208,8 +208,7 @@ static void arm_cpu_reset(DeviceState *dev)
>>                                            CPACR_EL1, ZEN, 3);
>>           /* with reasonable vector length */
>>           if (cpu_isar_feature(aa64_sve, cpu)) {
>> -            env->vfp.zcr_el[1] =
>> -                aarch64_sve_zcr_get_valid_len(cpu, cpu->sve_default_vq - 1);
>> +            env->vfp.zcr_el[1] = cpu->sve_default_vq - 1;
>>           }
> 
> I'm still not a fan of the zcr_el[] value not actually being
> a valid one. I'd rather we constrained it when we write the
> value into the field.

It is an architecturally valid value, exactly like the kernel might write while probing 
for supported vector lengths.  It will result in this, or the next smaller supported 
vector size, being selected.


r~