Messages in this thread Patch in this message | | | Date | Tue, 28 Mar 2023 11:54:44 +0100 | From | Jonathan Cameron <> | Subject | Re: [PATCH v2 2/5] perf: Allow a PMU to have a parent. |
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On Mon, 27 Mar 2023 13:04:08 -0400 "Liang, Kan" <kan.liang@linux.intel.com> wrote:
> On 2023-03-24 1:13 p.m., Jonathan Cameron wrote: > > Some PMUs have well defined parents such as PCI devices. > > As the device_initialize() and device_add() are all within > > pmu_dev_alloc() which is called from perf_pmu_register() > > there is no opportunity to set the parent from within a driver. > > > > Add a struct device *parent field to struct pmu and use that > > to set the parent. > > Why we want a PMU parent? Maybe I missed it. I don't see that the parent > is used anywhere.
This allows you to identify the association between PMU and the hardware related device that is providing it by looking at the directory structure in sysfs rather than putting them directly under /sys/devices.
ls -l /sys/bus/event_sources/devices/
... armv8_pmuv3_0 -> ../../../devices/arm8_pmuv3_0 ... breakpoint -> ../../../devices/breakpoint ... cpmu0 -> ../../../devices/pci0000:0c/0000:0c:00.0/0000:0d:00.0/cpmu0/cpmu0 etc
(the first cpmu0 is the parent registered as a child of the PCI EP and used for driver binding). So it's of use to userspace rather than in the kernel driver itself.
Note that almost nothing is normally in the top level /sys/devices other than event_sources - because nearly all other struct device instances created by subsystems have parents assigned.
On my system
ls /sys/devices
armv8_pmuv3_0 LNXSYSTEM:00 pci0000:0c pnp0 system uprobe breakpoint pci0000:00 platform software tracepoint virtual
+CC Greg KH for input on whether / why this make sense.
Thanks,
Jonathan
> > Thanks, > Kan > > > > > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> > > --- > > include/linux/perf_event.h | 1 + > > kernel/events/core.c | 1 + > > 2 files changed, 2 insertions(+) > > > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > > index d5628a7b5eaa..b99db1eda72c 100644 > > --- a/include/linux/perf_event.h > > +++ b/include/linux/perf_event.h > > @@ -303,6 +303,7 @@ struct pmu { > > > > struct module *module; > > struct device *dev; > > + struct device *parent; > > const struct attribute_group **attr_groups; > > const struct attribute_group **attr_update; > > const char *name; > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index fb3e436bcd4a..a84c282221f2 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -11367,6 +11367,7 @@ static int pmu_dev_alloc(struct pmu *pmu) > > > > dev_set_drvdata(pmu->dev, pmu); > > pmu->dev->bus = &pmu_bus; > > + pmu->dev->parent = pmu->parent; > > pmu->dev->release = pmu_dev_release; > > > > ret = dev_set_name(pmu->dev, "%s", pmu->name); >
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