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

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Date:   Thu, 9 Jul 2020 14:39:48 +0530
From:   Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:     Pratik Rajesh Sampat <psampat@...ux.ibm.com>
Cc:     mpe@...erman.id.au, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, benh@...nel.crashing.org,
        paulus@...ba.org, ego@...ux.vnet.ibm.com, svaidy@...ux.ibm.com,
        pratik.r.sampat@...il.com,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [PATCH 2/2] powerpc/powernv/idle: save-restore DAWR0,DAWRX0 for
 P10

On Fri, Jul 03, 2020 at 06:16:40PM +0530, Pratik Rajesh Sampat wrote:
> Additional registers DAWR0, DAWRX0 may be lost on Power 10 for
> stop levels < 4.

Adding Ravi Bangoria <ravi.bangoria@...ux.ibm.com> to the cc.

> 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>


The saving and restoration looks good to me. 
> ---
>  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..471d4a65b1fa 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)
> @@ -677,6 +679,10 @@ static unsigned long power9_idle_stop(unsigned long psscr, bool mmu_on)
>  		sprs.tscr	= mfspr(SPRN_TSCR);
>  		if (!firmware_has_feature(FW_FEATURE_ULTRAVISOR))
>  			sprs.ldbar = mfspr(SPRN_LDBAR);
> +		if (cpu_has_feature(CPU_FTR_ARCH_31)) {
> +			sprs.dawr0 = mfspr(SPRN_DAWR0);
> +			sprs.dawrx0 = mfspr(SPRN_DAWRX0);
> +		}
>


But this is within the if condition which says

	if ((psscr & PSSCR_RL_MASK) >= pnv_first_spr_loss_level)

This if condition is meant for stop4 and stop5 since these are stop
levels that have OPAL_PM_LOSE_HYP_CONTEXT set.

Since we can lose DAWR*, on states that lose limited hypervisor
context, such as stop0-2, we need to unconditionally save them
like AMR, IAMR etc.


>  		sprs_saved = true;
> 
> @@ -792,6 +798,10 @@ static unsigned long power9_idle_stop(unsigned long psscr, bool mmu_on)
>  	mtspr(SPRN_MMCR2,	sprs.mmcr2);
>  	if (!firmware_has_feature(FW_FEATURE_ULTRAVISOR))
>  		mtspr(SPRN_LDBAR, sprs.ldbar);
> +	if (cpu_has_feature(CPU_FTR_ARCH_31)) {
> +		mtspr(SPRN_DAWR0, sprs.dawr0);
> +		mtspr(SPRN_DAWRX0, sprs.dawrx0);
> +	}


Likewise, we need to unconditionally restore these SPRs.


> 
>  	mtspr(SPRN_SPRG3,	local_paca->sprg_vdso);
> 
> -- 
> 2.25.4
>