linux-kernel - Re: [PATCH 2/3] soc: sifive: Add SiFive private L2 cache PMU driver

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Message-ID: <20230623132402.GA17369@willie-the-truck>
Date:   Fri, 23 Jun 2023 14:24:08 +0100
From:   Will Deacon <will@...nel.org>
To:     Conor Dooley <conor@...nel.org>
Cc:     Eric Lin <eric.lin@...ive.com>,
        Conor Dooley <conor.dooley@...rochip.com>, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, palmer@...belt.com,
        paul.walmsley@...ive.com, aou@...s.berkeley.edu, maz@...nel.org,
        chenhuacai@...nel.org, baolu.lu@...ux.intel.com,
        kan.liang@...ux.intel.com, nnac123@...ux.ibm.com,
        pierre.gondois@....com, jgross@...e.com, chao.gao@...el.com,
        maobibo@...ngson.cn, linux-riscv@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        dslin1010@...il.com, Greentime Hu <greentime.hu@...ive.com>,
        Zong Li <zong.li@...ive.com>, Nick Hu <nick.hu@...ive.com>,
        mark.rutland@....com, arnd@...db.de
Subject: Re: [PATCH 2/3] soc: sifive: Add SiFive private L2 cache PMU driver

Hi folks,

On Wed, Jun 21, 2023 at 04:17:24PM +0100, Conor Dooley wrote:
> On Tue, Jun 20, 2023 at 11:14:32AM +0800, Eric Lin wrote:
> > On Fri, Jun 16, 2023 at 6:13 PM Conor Dooley <conor.dooley@...rochip.com> wrote:
> > > On Fri, Jun 16, 2023 at 02:32:09PM +0800, Eric Lin wrote:
> > > >  drivers/soc/sifive/Kconfig            |   9 +
> > > >  drivers/soc/sifive/Makefile           |   1 +
> > > >  drivers/soc/sifive/sifive_pl2.h       |  20 +
> > > >  drivers/soc/sifive/sifive_pl2_cache.c |  16 +
> > > >  drivers/soc/sifive/sifive_pl2_pmu.c   | 669 ++++++++++++++++++++++++++
> > >
> > > Perf drivers should be in drivers/perf, no?
> > >
> > 
> > But I grep perf_pmu_register(), it seems not all the pmu drivers are
> > in drivers/perf as below:
> > 
> > arch/arm/mach-imx/mmdc.c:517:   ret =
> > perf_pmu_register(&(pmu_mmdc->pmu), name, -1);
> > arch/arm/mm/cache-l2x0-pmu.c:552:       ret =
> > perf_pmu_register(l2x0_pmu, l2x0_name, -1);
> > ...
> > drivers/dma/idxd/perfmon.c:627: rc = perf_pmu_register(&idxd_pmu->pmu,
> > idxd_pmu->name, -1);
> > drivers/fpga/dfl-fme-perf.c:904:static int
> > fme_perf_pmu_register(struct platform_device *pdev,
> > drivers/fpga/dfl-fme-perf.c:929:        ret = perf_pmu_register(pmu, name, -1);
> > ...
> > drivers/gpu/drm/amd/amdgpu/amdgpu_pmu.c:549:    ret =
> > perf_pmu_register(&pmu_entry->pmu, pmu_name, -1);
> > drivers/gpu/drm/i915/i915_pmu.c:1190:   ret =
> > perf_pmu_register(&pmu->base, pmu->name, -1);
> > drivers/hwtracing/coresight/coresight-etm-perf.c:907:   ret =
> > perf_pmu_register(&etm_pmu, CORESIGHT_ETM_PMU_NAME, -1);
> > drivers/hwtracing/ptt/hisi_ptt.c:895:   ret =
> > perf_pmu_register(&hisi_ptt->hisi_ptt_pmu, pmu_name, -1);
> > drivers/iommu/intel/perfmon.c:570:      return
> > perf_pmu_register(&iommu_pmu->pmu, iommu_pmu->pmu.name, -1);
> > drivers/nvdimm/nd_perf.c:309:   rc = perf_pmu_register(&nd_pmu->pmu,
> > nd_pmu->pmu.name, -1);
> > ...
> > 
> > I just wondering what kind of pmu drivers should be in drivers/perf
> > and what kind of pmu drivers should not be in drivers/perf.
> > Thanks.
> 
> To be quite honest, I have no idea.
> I'm just a wee bit wary of taking anything that appears to have another
> home via drivers/soc. I'd rather break drivers out, using the aux bus or
> similar if need be, so that people who are knowledgeable in an area are
> CCed on patches.
> Hopefully Arnd or the Perf people can offer some guidance here. If it
> does go into drivers/soc, it'll need a review from someone knowledgeable
> of perf anyway.

I'm not territorial about the perf drivers at all, but L2CC PMUs like this
one probably fit pretty well in drivers/perf. The usual reason for putting
drivers elsewhere is if the PMU is tightly coupled with some other IP which
is handled by another subsystem (e.g. GPU).

Will