linux-kernel - Re: [PATCH v2 2/3] powerpc/powernv/idle: save-restore DAWR0,DAWRX0 for P10

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Date:   Fri, 24 Jul 2020 11:25:23 +1000
From:   Michael Neuling <mikey@...ling.org>
To:     Pratik Rajesh Sampat <psampat@...ux.ibm.com>, mpe@...erman.id.au,
        benh@...nel.crashing.org, paulus@...ba.org,
        ravi.bangoria@...ux.ibm.com, ego@...ux.vnet.ibm.com,
        svaidy@...ux.ibm.com, pratik.r.sampat@...il.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] powerpc/powernv/idle: save-restore DAWR0,DAWRX0
 for P10

On Fri, 2020-07-10 at 10:52 +0530, Pratik Rajesh Sampat wrote:
> Additional registers DAWR0, DAWRX0 may be lost on Power 10 for
> stop levels < 4.
> Therefore save the values of these SPRs before entering a  "stop"
> state and restore their values on wakeup.
> 
> Signed-off-by: Pratik Rajesh Sampat <psampat@...ux.ibm.com>
> ---
>  arch/powerpc/platforms/powernv/idle.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/arch/powerpc/platforms/powernv/idle.c
> b/arch/powerpc/platforms/powernv/idle.c
> index 19d94d021357..f2e2a6a4c274 100644
> --- a/arch/powerpc/platforms/powernv/idle.c
> +++ b/arch/powerpc/platforms/powernv/idle.c
> @@ -600,6 +600,8 @@ struct p9_sprs {
>  	u64 iamr;
>  	u64 amor;
>  	u64 uamor;
> +	u64 dawr0;
> +	u64 dawrx0;
>  };
>  
>  static unsigned long power9_idle_stop(unsigned long psscr, bool mmu_on)
> @@ -687,6 +689,10 @@ static unsigned long power9_idle_stop(unsigned long
> psscr, bool mmu_on)
>  	sprs.iamr	= mfspr(SPRN_IAMR);
>  	sprs.amor	= mfspr(SPRN_AMOR);
>  	sprs.uamor	= mfspr(SPRN_UAMOR);
> +	if (cpu_has_feature(CPU_FTR_ARCH_31)) {

Can you add a comment here saying even though DAWR0 is ARCH_30, it's only
required to be saved on 31. Otherwise this looks pretty odd.

> +		sprs.dawr0 = mfspr(SPRN_DAWR0);
> +		sprs.dawrx0 = mfspr(SPRN_DAWRX0);
> +	}
>  
>  	srr1 = isa300_idle_stop_mayloss(psscr);		/* go idle */
>  
> @@ -710,6 +716,10 @@ static unsigned long power9_idle_stop(unsigned long
> psscr, bool mmu_on)
>  		mtspr(SPRN_IAMR,	sprs.iamr);
>  		mtspr(SPRN_AMOR,	sprs.amor);
>  		mtspr(SPRN_UAMOR,	sprs.uamor);
> +		if (cpu_has_feature(CPU_FTR_ARCH_31)) {
> +			mtspr(SPRN_DAWR0, sprs.dawr0);
> +			mtspr(SPRN_DAWRX0, sprs.dawrx0);
> +		}
>  
>  		/*
>  		 * Workaround for POWER9 DD2.0, if we lost resources, the ERAT