linux-kernel - Re: [PATCH] Documentation: coresight: Update the generic device names

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Date:   Fri, 7 Jun 2019 09:58:54 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     Leo Yan <leo.yan@...aro.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Coresight ML <coresight@...ts.linaro.org>,
        Jon Corbet <corbet@....net>
Subject: Re: [PATCH] Documentation: coresight: Update the generic device names

On Fri, 7 Jun 2019 at 02:40, Suzuki K Poulose <suzuki.poulose@....com> wrote:
>
> Hi Leo,
>
> >>>>    A Coresight PMU works the same way as any other PMU, i.e the name of the PMU is
> >>>>    listed along with configuration options within forward slashes '/'.  Since a
> >>>>    Coresight system will typically have more than one sink, the name of the sink to
> >>>> -work with needs to be specified as an event option.  Names for sink to choose
> >>>> -from are listed in sysFS under ($SYSFS)/bus/coresight/devices:
> >>>> +work with needs to be specified as an event option.
> >>>> +On newer kernels the available sinks are listed in sysFS under:
> >>>> +($SYSFS)/bus/event_source/devices/cs_etm/sinks/
> >>>> -  root@...aro-nano:~# ls /sys/bus/coresight/devices/
> >>>> -          20010000.etf   20040000.funnel  20100000.stm  22040000.etm
> >>>> -          22140000.etm  230c0000.funnel  23240000.etm 20030000.tpiu
> >>>> -          20070000.etr     20120000.replicator  220c0000.funnel
> >>>> -          23040000.etm  23140000.etm     23340000.etm
> >>>> +  root@...alhost:/sys/bus/event_source/devices/cs_etm/sinks# ls
> >>>> +  tmc_etf0  tmc_etr0  tpiu0
> >>>> -  root@...aro-nano:~# perf record -e cs_etm/@...70000.etr/u --per-thread program
> >>>> +On older kernels, this may need to be found from the list of coresight devices,
> >>>> +available under ($SYSFS)/bus/coresight/devices/:
> >>>> +
> >>>> +  root@...alhost:/sys/bus/coresight/devices# ls
> >>>> +  etm0  etm1  etm2  etm3  etm4  etm5  funnel0  funnel1  funnel2  replicator0  stm0 tmc_etf0  tmc_etr0  tpiu0
> >>>> +
> >>>> +  root@...aro-nano:~# perf record -e cs_etm/@..._etr0/u --per-thread program
> >>>
> >>> On the "older" kernels you are referring to one would find the original naming
> >>> convention.  Everything else looks good to me.
> >>
> >> True, but do we care what we see there ? All we care about is the location,
> >> where to find them. I could fix it, if you think thats needed.
> >
> > IIUC, either the old kernel or newer kernel, both we can find the event
> > from ($SYSFS)/bus/event_source/devices/cs_etm/sinks/; the only
> > difference between them is the naming convention.
>
> The cs_etm/sinks was only added with the CPU-wide trace support. So, if someone
> refers to this document alone and then tries to do something on on older kernel,
> which is quite possible for a production device running a stable kernel, {s,}he
> might be surprised.
>
> >
> > So the doc can use the same location to find event for both new and
> > old kernel, and explain the naming convention difference?
>
> My question is really, does the naming convention matter ? What you see
> under the directory is the name. But yes, I am open to add a section to
> explain the fact that we changed the naming scheme, if everyone agrees
> to it.

I think it would be preferable to mention the change - just a small
section that describes what happened and the reason for doing so will
be fine.

>
> Cheers
> Suzuki