Re: [PATCH-for-10.1 1/4] target/sparc: Expose more CPU features

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 25/3/25 15:11, Richard Henderson wrote:
> On 3/25/25 05:39, Philippe Mathieu-Daudé wrote:
>> Various features were not displayed or settable from command line.
>>
>> Diff of 'qemu-system-sparc -cpu help':
>>
>>   ...
>>     TI-SuperSparc-60     (IU 40000000 FPU 00000000 MMU 01000800 NWINS 8)
>>     TI-SuperSparc-61     (IU 44000000 FPU 00000000 MMU 01000000 NWINS 8)
>>     TI-SuperSparc-II     (IU 40000000 FPU 00000000 MMU 08000000 NWINS 8)
>>   - LEON2                (IU f2000000 FPU 00080000 MMU f2000000 NWINS 8)
>>   - LEON3                (IU f3000000 FPU 00080000 MMU f3000000 NWINS 8)
>>   + LEON2                (IU f2000000 FPU 00080000 MMU f2000000 NWINS 
>> 8) +shutdown
>>   + LEON3                (IU f3000000 FPU 00080000 MMU f3000000 NWINS 
>> 8) +shutdown +asr17 +cachectrl +powerdown +casa
>>    Default CPU feature flags (use '-' to remove): mul div fsmuld
>>   -Available CPU feature flags (use '+' to add): float128
>>   +Available CPU feature flags (use '+' to add): shutdown asr17 
>> cachectrl powerdown casa float128
>>    Numerical features (use '=' to set): iu_version fpu_version 
>> mmu_version nwindows
>>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>> ---
>>   target/sparc/cpu.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/target/sparc/cpu.c b/target/sparc/cpu.c
>> index 57161201173..37406227cb7 100644
>> --- a/target/sparc/cpu.c
>> +++ b/target/sparc/cpu.c
>> @@ -548,6 +548,11 @@ static const sparc_def_t sparc_defs[] = {
>>   /* This must match sparc_cpu_properties[]. */
>>   static const char * const feature_name[] = {
>>       [CPU_FEATURE_BIT_FLOAT128] = "float128",
>> +    [CPU_FEATURE_BIT_TA0_SHUTDOWN] = "shutdown",
>> +    [CPU_FEATURE_BIT_POWERDOWN] = "powerdown",
>> +    [CPU_FEATURE_BIT_CACHE_CTRL] = "cachectrl",
>> +    [CPU_FEATURE_BIT_ASR17] = "asr17",
>> +    [CPU_FEATURE_BIT_CASA] = "casa",
>>   #ifdef TARGET_SPARC64
>>       [CPU_FEATURE_BIT_CMT] = "cmt",
>>       [CPU_FEATURE_BIT_GL] = "gl",
> 
> I'm not convinced this is a good idea.
> 
> The only effect of disabling these is to break LEON kernels. These 
> features are not exposed for kernel discovery, so you can't just turn 
> them on and have them used on supersparc either.  They will certainly 
> break anything sparc64.

OK. It seems there is a lot of hidden knowledge behind this features
array :)