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

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Message-Id: <1594619458.45vrahx59w.astroid@bobo.none>
Date:   Mon, 13 Jul 2020 15:52:32 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     benh@...nel.crashing.org, ego@...ux.vnet.ibm.com,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        mikey@...ling.org, mpe@...erman.id.au, paulus@...ba.org,
        pratik.r.sampat@...il.com,
        Pratik Rajesh Sampat <psampat@...ux.ibm.com>,
        ravi.bangoria@...ux.ibm.com, svaidy@...ux.ibm.com
Subject: Re: [PATCH v2 2/3] powerpc/powernv/idle: save-restore DAWR0, DAWRX0
 for P10

Excerpts from Pratik Rajesh Sampat's message of July 10, 2020 3:22 pm:
> 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.

Hmm, where do you get this from? Documentation I see says DAWR is lost
on POWER9 but not P10.

Does idle thread even need to save DAWR, or does it get switched when
going to a thread that has a watchpoint set?

Thanks,
Nick

> 
> 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)) {
> +		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
> -- 
> 2.25.4
> 
>