linux-kernel - Re: [PATCH v3 1/3] powerpc/powernv/idle: Replace CPU features checks with PVR checks

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Date:   Tue, 21 Jul 2020 15:54:14 +0530
From:   Pratik Sampat <psampat@...ux.ibm.com>
To:     Nicholas Piggin <npiggin@...il.com>, 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,
        svaidy@...ux.ibm.com
Subject: Re: [PATCH v3 1/3] powerpc/powernv/idle: Replace CPU features checks
 with PVR checks



On 20/07/20 5:30 am, Nicholas Piggin wrote:
> Excerpts from Pratik Rajesh Sampat's message of July 18, 2020 4:53 am:
>> As the idle framework's architecture is incomplete, hence instead of
>> checking for just the processor type advertised in the device tree CPU
>> features; check for the Processor Version Register (PVR) so that finer
>> granularity can be leveraged while making processor checks.
>>
>> Signed-off-by: Pratik Rajesh Sampat <psampat@...ux.ibm.com>
>> ---
>>   arch/powerpc/platforms/powernv/idle.c | 14 +++++++-------
>>   1 file changed, 7 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
>> index 2dd467383a88..f62904f70fc6 100644
>> --- a/arch/powerpc/platforms/powernv/idle.c
>> +++ b/arch/powerpc/platforms/powernv/idle.c
>> @@ -92,7 +92,7 @@ static int pnv_save_sprs_for_deep_states(void)
>>   		if (rc != 0)
>>   			return rc;
>>   
>> -		if (cpu_has_feature(CPU_FTR_ARCH_300)) {
>> +		if (pvr_version_is(PVR_POWER9)) {
>>   			rc = opal_slw_set_reg(pir, P9_STOP_SPR_MSR, msr_val);
>>   			if (rc)
>>   				return rc;
>> @@ -116,7 +116,7 @@ static int pnv_save_sprs_for_deep_states(void)
>>   				return rc;
>>   
>>   			/* Only p8 needs to set extra HID regiters */
>> -			if (!cpu_has_feature(CPU_FTR_ARCH_300)) {
>> +			if (!pvr_version_is(PVR_POWER9)) {
>>   
>>   				rc = opal_slw_set_reg(pir, SPRN_HID1, hid1_val);
>>   				if (rc != 0)
> What I think you should do is keep using CPU_FTR_ARCH_300 for this stuff
> which is written for power9 and we know is running on power9, because
> that's a faster test (static branch and does not have to read PVR. And
> then...
>
>> @@ -1205,7 +1205,7 @@ static void __init pnv_probe_idle_states(void)
>>   		return;
>>   	}
>>   
>> -	if (cpu_has_feature(CPU_FTR_ARCH_300))
>> +	if (pvr_version_is(PVR_POWER9))
>>   		pnv_power9_idle_init();
>>   
>>   	for (i = 0; i < nr_pnv_idle_states; i++)
> Here is where you would put the version check. Once we have code that
> can also handle P10 (either by testing CPU_FTR_ARCH_31, or by adding
> an entirely new power10 idle function), then you can add the P10 version
> check here.

Sure, it makes sense to make this check on the top level function and
retain CPU_FTR_ARCH_300 lower in the calls for speed.
I'll make that change.

Thanks
Pratik

> Thanks,
> Nick
>