linux-kernel - Re: [PATCH 1/1] Return EINVAL when precise

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Message-ID: <20200117140143.GD14879@hirez.programming.kicks-ass.net>
Date:   Fri, 17 Jan 2020 15:01:43 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Will Deacon <will@...nel.org>
Cc:     James Clark <james.clark@....com>,
        linux-arm-kernel@...ts.infradead.org, nd@....com,
        Mark Rutland <mark.rutland@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Tan Xiaojun <tanxiaojun@...wei.com>,
        Al Grant <al.grant@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] Return EINVAL when precise_ip perf events are
 requested on Arm

On Fri, Jan 17, 2020 at 12:39:21PM +0000, Will Deacon wrote:

> Perhaps a better way would be to expose something under sysfs, a bit like
> the caps directory for the SPE PMU, which identifies the fields of the attr
> structure that the driver does not ignore. I think doing this as an Arm-PMU
> specific thing initially would be fine, but it would be even better to have
> something where a driver can tell perf core about the parts it responds to
> and have this stuff populated automatically. The current design makes it
> inevitable that PMU drivers will have issues like the one you point out in
> the cover letter.
> 
> Thoughts?

We have PERF_PMU_CAP_ flags we could extend to that purpose.