Re: [PATCH v3 0/7] perf: Add ioctl for PMU driver configuration

From: Will Deacon
Date: Wed Aug 15 2018 - 05:39:10 EST

On Tue, Aug 14, 2018 at 01:42:27PM -0600, Mathieu Poirier wrote:
> On Tue, 14 Aug 2018 at 11:09, Kim Phillips <kim.phillips@xxxxxxx> wrote:
> > The other thing that's going on here is that I'm becoming numb to the
> > loathsome "failed to mmap with 12 (Cannot allocate memory)" being
> > returned no matter what the error is/was. E.g., an error that would
> > indicate a sense of non-implementation would be much better
> > appreciated than presumably what the above is doing, i.e., returning
> > -ENOMEM. That, backed up with specific details in the form of human
> > readable text in dmesg would be *most* welcome.
> As part of the refactoring of the code to support CPU-wide scenarios I
> intend to emit better diagnostic messages from the driver. Modifying
> rb_alloc_aux() to propagate the error message generated by the
> architecture specific PMUs doesn't look hard either and I _may_ get to
> it as part of this work.

For the record, I will continue to oppose PMU drivers that dump diagnostics
about user-controlled input into dmesg, but the coresight drivers are yours
so it's up to you and I won't get in the way!