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

[Suzuki K Poulose]

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@linaro-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@localhost:/sys/bus/event_source/devices/cs_etm/sinks# ls
> > > > +	tmc_etf0  tmc_etr0  tpiu0
> > > > -	root@linaro-nano:~# perf record -e cs_etm/@20070000.etr/u --per-thread program
> > > > +On older kernels, this may need to be found from the list of coresight devices,
> > > > +available under ($SYSFS)/bus/coresight/devices/:
> > > > +
> > > > +	root@localhost:/sys/bus/coresight/devices# ls
> > > > +	etm0  etm1  etm2  etm3  etm4  etm5  funnel0  funnel1  funnel2  replicator0  stm0 tmc_etf0  tmc_etr0  tpiu0
> > > > +
> > > > +	root@linaro-nano:~# perf record -e cs_etm/@tmc_etr0/u --per-thread program
> > >
> > > On the "older" kernels you are referring to one would find the original naming
> > > convention.  Everything else looks good to me.
> >
> > True, but do we care what we see there ? All we care about is the location,
> > where to find them. I could fix it, if you think thats needed.
>
> IIUC, either the old kernel or newer kernel, both we can find the event
> from ($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.

Cheers
Suzuki