Re: [PATCH v2 09/11] coresight: etm4x: docs: Update ABI doc for sysfs features added.

Mathieu Poirier
2019-09-03T22:52:01Z

On Tue, 3 Sep 2019 at 13:59, Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Thu, Aug 29, 2019 at 10:33:19PM +0100, Mike Leach wrote:
> > Update document to include the new sysfs features added during this
> > patchset.
> >
> > Updated to reflect the new sysfs component nameing schema.
> >
> > Signed-off-by: Mike Leach <mike.leach@linaro.org>
> > ---
> > .../testing/sysfs-bus-coresight-devices-etm4x | 183 +++++++++++-------
> > 1 file changed, 115 insertions(+), 68 deletions(-)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x b/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x
> > index 36258bc1b473..112c50ae9986 100644
> > --- a/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x
> > +++ b/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x
> > @@ -1,4 +1,4 @@
> > -What: /sys/bus/coresight/devices/<memory_map>.etm/enable_source
> > +What: /sys/bus/coresight/devices/etm<N>/enable_source
>
> You are renaming sysfs directories that have been around since:
>
> > Date: April 2015
>
> ???
>
> Really?
>
> That's brave.

When I worked on the coresight sysfs ABI a while back I specifically
added it at the "testing" level as I was well aware that things could
change in the future. According to the guidelines in the
documentation userspace can rely on it which was accurate since the
interface didn't change for 4 years. But the guidelines also mention
that changes can occur before the interfaces are move to stables, and
that programs are encouraged to manifest their interest by adding
their name to the "users" field.

The interface was changed in 5.2 to support coresight from ACPI and
make things easier to understand for users. It is a lot more
intuitive to associate an ETM tracer with the CPU it belongs to by
referring to the CPU number than the memory mapped address. Given the
"testing" status of the interface and the absence of registered users
I decided to move forward with the change. If "testing" is too strict
for that I suggest to add an "experimental" category where it would be
more acceptable to change things as subsystems mature.

Thanks,
Mathieu

>
>
> What tool did you just break?
>
> greg k-h