linux-kernel - Re: [PATCH V3] perf vendor events riscv: add T-HEAD C9xx JSON file

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Message-ID: <20230624-supermom-disparity-37546ffed0a4@spud>
Date:   Sat, 24 Jun 2023 09:54:50 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Inochi Amaoto <inochiama@...look.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Nikita Shubin <n.shubin@...ro.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH V3] perf vendor events riscv: add T-HEAD C9xx JSON file

On Fri, Jun 23, 2023 at 09:35:01PM -0700, Namhyung Kim wrote:
> On Fri, Jun 23, 2023 at 6:33 PM Inochi Amaoto <inochiama@...look.com> wrote:

> >
> > As for c9xx wildcard, the T-HEAD provides a `MCPUID` vendor CSR to allow
> > its CKLINK to get the detail CPU info. The format of this CSR are:
> >
> > ------------------------------------------------
> > |31   28|27  26|25    22|21   18|17    8|7    0|
> > | index | WLRL | family | class | model | WLRL |
> > ------------------------------------------------
> >
> > And for C9xx series (only index 0000 is vaild for us, as `MCPUID` also
> > provides other index).
> >
> > | 0000 | xx | 0100 | class | xxxxxxxxxx | xxxxxxxx |
> >
> > The class codes are:
> >
> > C910: 0011
> > c906: 0100
> >
> > The CSR is a M-mode only CSR, so now I'm exploring a clean way to
> > integrate this CSR into the kernel. Any advice?

See for example how riscv_cpuinfo_starting() reads mvendorid & Co.

> I don't know about the details.  Is this CSR available from user space?
> If not, you could add it somewhere in the sysfs.

Machine mode is the highest privilege level, Supervisor mode is next &
User mode is the lowest. Typically the kernel runs in Supervisor mode.

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