Messages in this thread | | | Date | Wed, 29 Mar 2023 09:55:04 +0100 | From | Jonathan Cameron <> | Subject | Re: [PATCH v2 2/5] perf: Allow a PMU to have a parent. |
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On Tue, 28 Mar 2023 13:01:08 +0200 Greg KH <gregkh@linuxfoundation.org> wrote:
> On Tue, Mar 28, 2023 at 11:54:44AM +0100, Jonathan Cameron wrote: > > 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. > > That doesn't make sense, nothing should be in /sys/devices/ EXCEPT the > root device of busses. Everything else is wrong and should have their > code fixed up (i.e. "breakpoint", "software", etc.)
Thanks Greg.
I was thinking to cycle back round to that once I'd got agreement on 'some' devices, but great to have clarity from the start that these should all have parents.
For a few cases the parent is not immediately obvious but we'll figure it out.
Jonathan
> > thanks, > > greg k-h
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