Messages in this thread | | | Date | Wed, 29 Mar 2023 11:03:06 +0200 | From | Greg KH <> | Subject | Re: [PATCH v2 2/5] perf: Allow a PMU to have a parent. |
| |
On Wed, Mar 29, 2023 at 09:55:04AM +0100, Jonathan Cameron wrote: > 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.
If there is no "real" parent, then it is a virtual device and belongs under the "virtual" directory. Otherwise why are these "devices" at all with such generic names?
thanks,
greg k-h
| |