Marvell: hw perfevents: unable to count PMU IRQs

[Robin Murphy]

On 2021-03-25 21:39, Paul Menzel wrote:
> Dear Linux folks,
> 
> 
> On the Marvell Prestera switch, Linux 5.10.4 prints the error (with an 
> additional info level message) below.
> 
>      [    0.000000] Linux version 5.10.4 (robimarko at onlbuilder9) 
> (aarch64-linux-gnu-gcc (Debian 6.3.0-18) 6.3.0 20170516, GNU ld (GNU 
> Binutils for Debian) 2.28) #1 SMP PREEMPT Thu Mar 11 10:22:09 UTC 2021
>      […]
>      [    1.996658] hw perfevents: unable to count PMU IRQs
>      [    2.001825] hw perfevents: /ap806/config-space at f0000000/pmu: 
> failed to register PMU devices!
> 
> ```
> # lscpu
> Architecture:          aarch64
> Byte Order:            Little Endian
> CPU(s):                4
> On-line CPU(s) list:   0-3
> Thread(s) per core:    1
> Core(s) per socket:    4
> Socket(s):             1
> NUMA node(s):          1
> Model:                 1
> BogoMIPS:              50.00
> L1d cache:             32K
> L1i cache:             48K
> L2 cache:              512K
> NUMA node0 CPU(s):     0-3
> Flags:                 fp asimd evtstrm aes pmull sha1 sha2 crc32 cpuid
> # cat /proc/cpuinfo
> processor       : 0
> BogoMIPS        : 50.00
> Features        : fp asimd evtstrm aes pmull sha1 sha2 crc32 cpuid
> CPU implementer : 0x41
> CPU architecture: 8
> CPU variant     : 0x0
> CPU part        : 0xd08
> CPU revision    : 1
> […]
> ```
> 
> Please find the output of `dmesg` attached.
> 
> How can the IRQs be counted?

Well, that message simply means we got an error back from 
platform_irq_count(), which in turn implies that 
platform_get_irq_optional() failed. Most likely we got -EPROBE_DEFER 
back from of_irq_get() because the relevant interrupt controller wasn't 
ready by that point - especially since that's the o9nly error code that 
platform_irq_cont() will actually pass. It looks like that should end up 
getting propagated all the way out appropriately, so the PMU driver 
should defer and be able to probe OK once the mvebu-pic driver has 
turned up to provide its IRQ. We could of course do a better job of not 
shouting error messages for a non-fatal condition....

As for why the PMU doesn't eventually show up, my best guess would be 
either an issue with the mvebu-pic driver itself probing, and/or perhaps 
something in fw_devlink going awry - inspecting sysfs should shed a bit 
more light on those.

Robin.