[Mesa-dev] [PATCH v2 1/2] gallium: Enable ARM NEON/VFP CPU detection.

[Grazvydas Ignotas]

On Fri, Apr 14, 2017 at 12:08 AM, Eric Anholt <eric at anholt.net> wrote:

> I wrote this code with reference to pixman, though I've only decided to
> cover Linux (what I'm testing) and Android (seems obvious enough).  Linux
> has getauxval() as a cleaner interface to the /proc entry, but it's more
> glibc-specific and I didn't want to add detection for that.
>

But now you have to worry about running out of file descriptors and
forking. Mesa already does checks like
#if defined(__GLIBC__) && ((__GLIBC__ > 2) || ((__GLIBC__ == 2) &&
(__GLIBC_MINOR__ >= 19)))
but it's up to you I guess.


> This will be used to enable NEON at runtime on ARMv6 builds of vc4.
>
> v2: Actually initialize the temp vars in the Android path (noticed by
>     daniels)
> ---
>  src/gallium/auxiliary/util/u_cpu_detect.c | 46
> +++++++++++++++++++++++++++++++
>  src/gallium/auxiliary/util/u_cpu_detect.h |  2 ++
>  2 files changed, 48 insertions(+)
>
> diff --git a/src/gallium/auxiliary/util/u_cpu_detect.c
> b/src/gallium/auxiliary/util/u_cpu_detect.c
> index 845fc6b34d5c..c9083fed63af 100644
> --- a/src/gallium/auxiliary/util/u_cpu_detect.c
> +++ b/src/gallium/auxiliary/util/u_cpu_detect.c
> @@ -59,12 +59,18 @@
>
>  #if defined(PIPE_OS_LINUX)
>  #include <signal.h>
> +#include <fcntl.h>
> +#include <elf.h>
>  #endif
>
>  #ifdef PIPE_OS_UNIX
>  #include <unistd.h>
>  #endif
>
> +#if defined(PIPE_OS_ANDROID)
> +#include <cpu-features.h>
> +#endif
> +
>  #if defined(PIPE_OS_WINDOWS)
>  #include <windows.h>
>  #if defined(PIPE_CC_MSVC)
> @@ -294,6 +300,40 @@ PIPE_ALIGN_STACK static inline boolean
> sse2_has_daz(void)
>
>  #endif /* X86 or X86_64 */
>
> +#if defined(PIPE_ARCH_ARM)
> +static void
> +check_os_arm_support(void)
> +{
> +#if defined(PIPE_OS_ANDROID)
> +   AndroidCpuFamily cpu_family = android_getCpuFamily();
> +   uint64_t cpu_features = android_getCpuFeatures();
> +
> +   if (cpu_family == ANDROID_CPU_FAMILY_ARM) {
> +      if (cpu_features & ANDROID_CPU_ARM_FEATURE_VFPv3)
> +         util_cpu_caps.has_vfp = 1;
> +      if (cpu_features & ANDROID_CPU_ARM_FEATURE_NEON)
> +         util_cpu_caps.has_neon = 1;
> +   }
> +#elif defined(PIPE_OS_LINUX)
> +    Elf32_auxv_t aux;
> +    int fd;
> +
> +    fd = open("/proc/self/auxv", O_RDONLY);
>

O_CLOEXEC?


> +    if (fd >= 0) {
> +       while (read(fd, &aux, sizeof(Elf32_auxv_t)) ==
> sizeof(Elf32_auxv_t)) {
> +          if (aux.a_type == AT_HWCAP) {
> +             uint32_t hwcap = aux.a_un.a_val;
> +
> +             util_cpu_caps.has_vfp = (hwcap >> 6) & 1;
> +             util_cpu_caps.has_neon = (hwcap >> 12) & 1;
>

break;


> +          }
> +       }
> +       close (fd);
> +    }
> +#endif /* PIPE_OS_LINUX */
> +}
> +#endif /* PIPE_ARCH_ARM */
> +
>

Gražvydas
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