Re: [PATCH] s390/pai: Simplify pai_init() and always return -ENODEV on failure

[Thomas Richter <tmricht@linux.ibm.com>]

On 9/14/26 14:14, Heiko Carstens wrote:
> On Thu, Sep 03, 2026 at 10:15:57AM +0200, Thomas Richter wrote:
>> Code simplification and remove variable state.
>> Return -ENODEV in all failures to indicate the PAI PMUs are not
>> available.
> 
> Why do you want to hide different error / return codes? That makes
> debugging in case of an error more difficult.

Well, hiding was not the intent.

The kernel common code does a lot of checks at event creation,
then calls the PMU event_init() call back to install the event.
When this fails the return code is checked and further action
depends on this return code. See

  perf_init_event()
  +--> perf_try_event_init()
       +--> PMU->event_init()

See include/linux/perf_event.h for return code meanings.

When we return the value from cpuhp_setup_state(), it must no be
-ENOENT and some other values. Because those are used for postprocessing.

Thats why I always return -ENODEV, meaning event is valid for PMU, but
PMU not operational. I thouhgt this might fit best.
  
-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH

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