linux-kernel - Re: [PATCH 2/8] perf/arm-cmn: Fix CCLA register offset

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Message-ID: <b54f8cf-d37d-6eb3-cbac-9852a6802b7e@os.amperecomputing.com>
Date: Fri, 23 Aug 2024 16:18:45 -0700 (PDT)
From: Ilkka Koskinen <ilkka@...amperecomputing.com>
To: Robin Murphy <robin.murphy@....com>
cc: Mark Rutland <mark.rutland@....com>, will@...nel.org, 
    linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
    ilkka@...amperecomputing.com
Subject: Re: [PATCH 2/8] perf/arm-cmn: Fix CCLA register offset


Hi Robin,

Sorry for replying late but I just got back from my vacation


On Fri, 16 Aug 2024, Robin Murphy wrote:
> On 16/08/2024 11:00 am, Mark Rutland wrote:
>> On Fri, Aug 09, 2024 at 08:15:41PM +0100, Robin Murphy wrote:
>>> Apparently pmu_event_sel is offset by 8 for all CCLA nodes, not just
>>> the CCLA_RNI combination type.
>> 
>> Was there some reason we used to think that was specific to CCLA_RNI
>> nodes, or was that just an oversight?
>
> I imagine it was just oversight/confusion helped by the original r0p0 TRM 
> listing both a por_ccla_pmu_event_sel and a por_ccla_rni_pmu_event_sel as 
> CCLA registers, which I could well believe I misread at a glance while 
> scrolling up and down.
>
>> Looking at the CMN-700 TRM and scanning for pmu_event_sel, we have:
>>
>> 	16'h2000	por_ccg_ha_pmu_event_sel
>> 	16'h2000	por_ccg_ra_pmu_event_sel
>> 	16'h2008	por_ccla_pmu_event_sel
>> 	16'h2000	por_dn_pmu_event_sel
>> 	16'h2000	cmn_hns_pmu_event_sel
>> 	16'h2000	por_hni_pmu_event_sel
>> 	16'h2008	por_hnp_pmu_event_sel
>> 	16'h2000	por_mxp_pmu_event_sel
>> 	16'h2000	por_rnd_pmu_event_sel
>> 	16'h2000	por_rni_pmu_event_sel
>> 	16'h2000	por_sbsx_pmu_event_sel
>> 
>>> Fixes: 23760a014417 ("perf/arm-cmn: Add CMN-700 support")
>>> Signed-off-by: Robin Murphy <robin.murphy@....com>
>>> ---
>>>   drivers/perf/arm-cmn.c | 5 ++++-
>>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>> 
>>> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
>>> index fd2122a37f22..0e2e12e2f4fb 100644
>>> --- a/drivers/perf/arm-cmn.c
>>> +++ b/drivers/perf/arm-cmn.c
>>> @@ -2393,10 +2393,13 @@ static int arm_cmn_discover(struct arm_cmn *cmn, 
>>> unsigned int rgn_offset)
>>>   			case CMN_TYPE_CXHA:
>>>   			case CMN_TYPE_CCRA:
>>>   			case CMN_TYPE_CCHA:
>>> -			case CMN_TYPE_CCLA:
>>>   			case CMN_TYPE_HNS:
>>>   				dn++;
>>>   				break;
>>> +			case CMN_TYPE_CCLA:
>>> +				dn->pmu_base += CMN_HNP_PMU_EVENT_SEL;
>>> +				dn++;
>>> +				break;
>> 
>> When reading this for the first time, it looks like a copy-paste error
>> since CMN_HNP_PMU_EVENT_SEL doesn't have any obvious relationship with
>> CCLA nodes.
>> 
>> I reckon it'd be worth adding CMN_CCLA_PMU_EVENT_SEL, and replacing the
>> existing comment above the definition of CMN_HNP_PMU_EVENT_SEL, e.g.
>> 
>> /*
>>   * Some nodes place common registers at different offsets from most
>>   * other nodes.
>>   */
>> #define CMN_HNP_PMU_EVENT_SEL		0x008
>> #define CMN_CCLA_PMU_EVENT_SEL		0x008
>> 
>> That way the switch looks less suspicious, and the comment is a bit more
>> helpful to anyone trying to figure out what's going on here.
>
> Sure, that's a reasonable argument.
>
>> With that:
>> 
>> Acked-by: Mark Rutland <mark.rutland@....com>
>
> Thanks,
> Robin.


I like Mark's idea. With the change,

Reviewed-by: Ilkka Koskinen <ilkka@...amperecomputing.com>

Cheers, Ilkka

>
>> 
>> Mark.
>>
>>>   			/* Nothing to see here */
>>>   			case CMN_TYPE_MPAM_S:
>>>   			case CMN_TYPE_MPAM_NS:
>>> -- 
>>> 2.39.2.101.g768bb238c484.dirty
>>> 
>