Re: [2/2] coresight: Fix reference count for software sources

[Suzuki K Poulose]

On 14/03/17 17:40, Mathieu Poirier wrote:
> On 14 March 2017 at 11:32, Mathieu Poirier <mathieu.poirier@xxxxxxxxxx> wrote:
> > From: "Suzuki K. Poulose" <Suzuki.Poulose@xxxxxxx>
> >
> > For software sources (i.e STM), there could be multiple agents
> > generating the trace data, unlike the ETMs. So we need to
> > properly do the accounting for the active number of users
> > to disable the device when the last user goes away. Right
> > now, the reference counting is broken for sources as we skip
> > the actions when we detect that the source is enabled.
> >
> > This patch fixes the problem by adding the refcounting for
> > software sources, even when they are enabled.
> >
> > Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> > Reported-by: Robert Walker <robert.walker@xxxxxxx>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > ---
> >  drivers/hwtracing/coresight/coresight.c | 13 +++++++++++--
> >  1 file changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c
> > index 34cd1ed..2da9e39 100644
> > --- a/drivers/hwtracing/coresight/coresight.c
> > +++ b/drivers/hwtracing/coresight/coresight.c
> > @@ -552,6 +552,7 @@ int coresight_enable(struct coresight_device *csdev)
> >         int cpu, ret = 0;
> >         struct coresight_device *sink;
> >         struct list_head *path;
> > +       enum coresight_dev_subtype_source subtype = csdev->subtype.source_subtype;
>
> Checkpatch.pl complains about a line over 80 characters.
>
> >         mutex_lock(&coresight_mutex);
> >
> > @@ -559,8 +560,16 @@ int coresight_enable(struct coresight_device *csdev)
> >         if (ret)
> >                 goto out;
> >
> > -       if (csdev->enable)
> > +       if (csdev->enable) {
> > +               /*
> > +                * There could be multiple applications driving the software
> > +                * source. So keep the refcount for each such user when the
> > +                * source is already enabled.
> > +                */
> > +               if (subtype == CORESIGHT_DEV_SUBTYPE_SOURCE_SOFTWARE)
> > +                       atomic_inc(csdev->refcnt);
> >                 goto out;
> > +       }

Btw, should we allow the user to turn on the STM from sysfs (echo 1 > $STM/enable_source) ?
All STM users should set their policy via ioctls and that in turn turns the device on. So
it doesn't make sense for enable_source to really enable the hardware unless someone really
opens it.

Chunyan, Mathieu,

thoughts ?

Suzuki