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    SubjectRe: [PATCH v3 0/7] perf: Add ioctl for PMU driver configuration
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    On 08/16/2018 08:28 PM, Mathieu Poirier wrote:
    > On Wed, 15 Aug 2018 at 09:28, Kim Phillips <kim.phillips@arm.com> wrote:
    >>
    >> On Wed, 15 Aug 2018 10:39:13 +0100
    >> Will Deacon <will.deacon@arm.com> wrote:
    >>
    >>> 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@arm.com> 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!
    >>
    >> That sounds technically self-contradicting to me. Why shouldn't
    >> coresight share the same policies as those used for PMU drivers? Or
    >> why not allow the individual vendor PMU driver authors control the
    >> level of user-friendliness of their own drivers?
    >>
    >> That being said, Matheiu, would you accept patches that make coresight
    >> more verbose in dmesg?
    >
    > It depends on the issue you're hoping to address. I'd rather see the
    > root cause of the problem fixed than adding temporary code. Suzuki
    > added the ETR perf API and I'm currently working on CPU-wide
    > scenarios. From there and with regards to what can happen in
    > setup_aux(), we should have things covered.

    I think the main issue is the lack of error code propagation from
    setup_aux() back to the perf_aux_output_handle_begin(), which always
    return -ENOMEM. If we fix that, we could get better idea of whats
    wrong.


    If someone is planning to add verbose messages, they may do so by adding
    dev_dbg() / pr_debug(), which can be turned on as and when needed.

    Suzuki

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