Re: [PATCH v2 3/3] perf/smmuv3: Synthesize IIDR from CoreSight ID registers

[Leo Yan <leo.yan@linaro.org>]

On Tue, Dec 07, 2021 at 12:48:13PM +0000, Robin Murphy wrote:
> On 2021-12-07 12:28, John Garry via iommu wrote:
> > On 07/12/2021 12:04, Robin Murphy wrote:
> > > > > 
> > > > So is there some userspace part to go with this now?
> > > 
> > > FWIW I've not looked into it - is it just a case of someone knocking
> > > out some JSON from the MMU-600/700 TRMs, or is there still mroe to
> > > do?
> > 
> > That should just be it.

Hope I didn't arrive too late :)

Yes, I think we just missed two things: the DT binding for SMMUv3 PMU
which is just addressed by this patchset; and the PMU event aliasing
for SMMUv3 PMU, before I inquired with John and John said he would
upstream the related patches after kernel can export a IIDR value via
sysfs node.

Seems to me, after this patchset for DT binding and PMU event alias
patches are landed to the mainline kernel, it would be perfect.

> > > I had the impression that *some* part of the process was stalled
> > > until implementations can start providing meaningful IIDRs, but I
> > > wasn't sure whether that was tooling or just data. I just work the
> > > low-level enablement angle :)
> > 
> > Tooling should be ok, but I would just like to see more of these JSONs
> > so any tooling issues can be ironed out.
> 
> Sounds good - Jean, Leo, is that something Linaro might like to pick up as
> part of the PMCG interest, or shall I make a note on my to-do list for the
> new year?

I took a look for current patch for using PIDR to synthesize IIDR, it
looks good to me.  But I tested it on Hisilicon D06 board and observed
the composed IIDR values are still zeros.

I added a printk sentence to dump iidr value at the end of the function
smmu_pmu_get_iidr():

  leoy@ubuntu:~$ dmesg | grep iidr
  [   28.674087] arm-smmu-v3-pmcg arm-smmu-v3-pmcg.8.auto: iidr=0x0
  [   28.705239] arm-smmu-v3-pmcg arm-smmu-v3-pmcg.9.auto: iidr=0x0
  [   28.729924] arm-smmu-v3-pmcg arm-smmu-v3-pmcg.10.auto: iidr=0x0
  [   28.754855] arm-smmu-v3-pmcg arm-smmu-v3-pmcg.11.auto: iidr=0x0
  [   28.779811] arm-smmu-v3-pmcg arm-smmu-v3-pmcg.12.auto: iidr=0x0
  [   28.804755] arm-smmu-v3-pmcg arm-smmu-v3-pmcg.13.auto: iidr=0x0
  [   28.829825] arm-smmu-v3-pmcg arm-smmu-v3-pmcg.14.auto: iidr=0x0
  [   28.854767] arm-smmu-v3-pmcg arm-smmu-v3-pmcg.15.auto: iidr=0x0

Please confirm if this is expected or not?  I think this might
introduce difficulty for John for the PMU event alias patches, which
is dependent on a non-zero IIDR.

At last, very appreciate your (Jean-Philippe, Robin and John) help!

Thanks,
Leo