[Mesa-dev] [PATCH] gallium/util: fix nondeterministic avx512 detection

[Rowley, Timothy O]

There weren’t any direct users of the avx512 features yet, but probably worth proposing for stable pickup.

Thanks.

-Tim

> On Jul 19, 2017, at 2:40 PM, Roland Scheidegger <sroland at vmware.com> wrote:
> 
> Makes sense to me.
> Probably should go into stable?
> 
> Reviewed-by: Roland Scheidegger <sroland at vmware.com>
> 
> Am 19.07.2017 um 21:29 schrieb Tim Rowley:
>> cpuid.7 requires cx=0 to select the extended feature leaf.
>> 
>> avx512 detection was using the non-indexed cpuid resulting
>> in random non-detection of avx512.
>> ---
>> src/gallium/auxiliary/util/u_cpu_detect.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/src/gallium/auxiliary/util/u_cpu_detect.c b/src/gallium/auxiliary/util/u_cpu_detect.c
>> index 3d6ccb5822..4e71041bc9 100644
>> --- a/src/gallium/auxiliary/util/u_cpu_detect.c
>> +++ b/src/gallium/auxiliary/util/u_cpu_detect.c
>> @@ -438,7 +438,7 @@ util_cpu_detect(void)
>>           (xgetbv() & (0x7 << 5)) && // OPMASK: upper-256 enabled by OS
>>           ((xgetbv() & 6) == 6)) { // XMM/YMM enabled by OS
>>          uint32_t regs3[4];
>> -         cpuid(0x00000007, regs3);
>> +         cpuid_count(0x00000007, 0x00000000, regs3);
>>          util_cpu_caps.has_avx512f    = (regs3[1] >> 16) & 1;
>>          util_cpu_caps.has_avx512dq   = (regs3[1] >> 17) & 1;
>>          util_cpu_caps.has_avx512ifma = (regs3[1] >> 21) & 1;
>> 
>