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

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Message-ID: <87fdebb1-93e1-a59d-f582-784ee1c19279@linux.ibm.com>
Date:   Thu, 9 Jul 2020 16:51:04 +0530
From:   Pratik Sampat <psampat@...ux.ibm.com>
To:     ego@...ux.vnet.ibm.com
Cc:     mpe@...erman.id.au, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, benh@...nel.crashing.org,
        paulus@...ba.org, 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 09/07/20 2:39 pm, Gautham R Shenoy wrote:
> 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.
>
Right, shallow states too loose DAWR/X. Thanks for pointing it out.
I'll fix this and resend.

>>   		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
>>
Thanks
Pratik