Re: [PATCH v2 6/7] powerpc/dt_cpu_ftrs: Add MMA feature

From: "Paul A. Clarke" <pc@us.ibm.com>
To: Alistair Popple <alistair@popple.id.au>
Cc: aneesh.kumar@linux.ibm.com, mikey@neuling.org,
	linuxppc-dev@lists.ozlabs.org, npiggin@gmail.com
Subject: Re: [PATCH v2 6/7] powerpc/dt_cpu_ftrs: Add MMA feature
Date: Tue, 19 May 2020 12:51:53 -0500	[thread overview]
Message-ID: <20200519175153.GE24922@oc3272150783.ibm.com> (raw)
In-Reply-To: <20200519003157.31946-7-alistair@popple.id.au>

On Tue, May 19, 2020 at 10:31:56AM +1000, Alistair Popple wrote:
> Matrix multiple accumulate (MMA) is a new feature added to ISAv3.1 and

Conclusion is that this should be "Matrix-Multiply Assist", but then there
are a couple more below...

> POWER10. Support on powernv can be selected via a firmware CPU device
> tree feature which enables it via a PCR bit.
> 
> Signed-off-by: Alistair Popple <alistair@popple.id.au>
> ---
>  arch/powerpc/include/asm/reg.h    |  3 ++-
>  arch/powerpc/kernel/dt_cpu_ftrs.c | 17 ++++++++++++++++-
>  2 files changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
> index 1931b1142599..c446863a40cf 100644
> --- a/arch/powerpc/include/asm/reg.h
> +++ b/arch/powerpc/include/asm/reg.h
> @@ -479,7 +479,8 @@
>  #define   PCR_VEC_DIS	(__MASK(63-0))	/* Vec. disable (bit NA since POWER8) */
>  #define   PCR_VSX_DIS	(__MASK(63-1))	/* VSX disable (bit NA since POWER8) */
>  #define   PCR_TM_DIS	(__MASK(63-2))	/* Trans. memory disable (POWER8) */
> -#define   PCR_HIGH_BITS	(PCR_VEC_DIS | PCR_VSX_DIS | PCR_TM_DIS)
> +#define   PCR_MMA_DIS	(__MASK(63-3)) /* Matrix-Multiply Accelerator */

also here.

> +#define   PCR_HIGH_BITS	(PCR_MMA_DIS | PCR_VEC_DIS | PCR_VSX_DIS | PCR_TM_DIS)
>  /*
>   * These bits are used in the function kvmppc_set_arch_compat() to specify and
>   * determine both the compatibility level which we want to emulate and the
> diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
> index 93c340906aad..e7540ee5cad8 100644
> --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
> +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
> @@ -75,6 +75,7 @@ static struct {
>  	u64	lpcr_clear;
>  	u64	hfscr;
>  	u64	fscr;
> +	u64	pcr;
>  } system_registers;
> 
>  static void (*init_pmu_registers)(void);
> @@ -102,7 +103,7 @@ static void __restore_cpu_cpufeatures(void)
>  	if (hv_mode) {
>  		mtspr(SPRN_LPID, 0);
>  		mtspr(SPRN_HFSCR, system_registers.hfscr);
> -		mtspr(SPRN_PCR, PCR_MASK);
> +		mtspr(SPRN_PCR, system_registers.pcr);
>  	}
>  	mtspr(SPRN_FSCR, system_registers.fscr);
> 
> @@ -555,6 +556,18 @@ static int __init feat_enable_large_ci(struct dt_cpu_feature *f)
>  	return 1;
>  }
> 
> +static int __init feat_enable_mma(struct dt_cpu_feature *f)
> +{
> +	u64 pcr;
> +
> +	feat_enable(f);
> +	pcr = mfspr(SPRN_PCR);
> +	pcr &= ~PCR_MMA_DIS;
> +	mtspr(SPRN_PCR, pcr);
> +
> +	return 1;
> +}
> +
>  struct dt_cpu_feature_match {
>  	const char *name;
>  	int (*enable)(struct dt_cpu_feature *f);
> @@ -629,6 +642,7 @@ static struct dt_cpu_feature_match __initdata
>  	{"vector-binary16", feat_enable, 0},
>  	{"wait-v3", feat_enable, 0},
>  	{"prefix-instructions", feat_enable, 0},
> +	{"matrix-multiply-accumulate", feat_enable_mma, 0},

and presumably here as well.

>  };

PC