Subject: Re: [PATCH v2 1/7] powerpc: Add new HWCAP bits

From: Michael Ellerman <[email-masked]>
Date: Wed, 20 May 2020 12:42:09 +1000

Alistair Popple <[email-masked]> writes:
> POWER10 introduces two new architectural features - ISAv3.1 and matrix
> multiply accumulate (MMA) instructions. Userspace detects the presence
> of these features via two HWCAP bits introduced in this patch. These
> bits have been agreed to by the compiler and binutils team.

Do we have an explanation of why we're exposing MMA separately.

I believe it's because ISA v3.1 says that MMA is optional, in the table
on page ix?

cheers

> diff --git a/arch/powerpc/include/uapi/asm/cputable.h b/arch/powerpc/include/uapi/asm/cputable.h
> index 540592034740..2692a56bf20b 100644
> --- a/arch/powerpc/include/uapi/asm/cputable.h
> +++ b/arch/powerpc/include/uapi/asm/cputable.h
> @@ -50,6 +50,8 @@
>  #define PPC_FEATURE2_DARN		0x00200000 /* darn random number insn */
>  #define PPC_FEATURE2_SCV		0x00100000 /* scv syscall */
>  #define PPC_FEATURE2_HTM_NO_SUSPEND	0x00080000 /* TM w/out suspended state */
> +#define PPC_FEATURE2_ARCH_3_1		0x00040000 /* ISA 3.1 */
> +#define PPC_FEATURE2_MMA		0x00020000 /* Matrix Multiply Accumulate */
>  
>  /*
>   * IMPORTANT!
> -- 
> 2.20.1