Re: [PATCH V2 06/15] coresight: tmc: making prepare/unprepare functions generic

[Suzuki K Poulose]

On 19/04/16 16:22, Mathieu Poirier wrote:
> On 19 April 2016 at 06:30, Suzuki K Poulose <Suzuki.Poulose@xxxxxxx> wrote:
> > On 12/04/16 18:54, Mathieu Poirier wrote:
> > > Dealing with HW related matters in tmc_read_prepare/unprepare
> > > becomes convoluted when many cases need to be handled distinctively.
> > >
> > > As such moving processing related to HW setup to individual driver
> > > files and keep the core driver generic.
> > >
> > > Signed-off-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> > > ---
> > >    drivers/hwtracing/coresight/coresight-tmc-etf.c | 62
> > > ++++++++++++++++++++++++-
> > >    drivers/hwtracing/coresight/coresight-tmc-etr.c | 42 ++++++++++++++++-
> > >    drivers/hwtracing/coresight/coresight-tmc.c     | 55
> > > +++++-----------------
> > >    drivers/hwtracing/coresight/coresight-tmc.h     |  8 ++--
> > >    4 files changed, 117 insertions(+), 50 deletions(-)
> >
> > > diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> > > b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> > > index 910d6f3b7d26..495540e9064d 100644
> > > --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> > > +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> > > @@ -70,7 +70,7 @@ static void tmc_etr_dump_hw(struct tmc_drvdata *drvdata)
> > >                  drvdata->buf = drvdata->vaddr;
> > >    }
> > >
> > > -void tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
> > > +static void tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
> > >    {
> > >          CS_UNLOCK(drvdata->base);
> > >
> > > @@ -126,3 +126,43 @@ static const struct coresight_ops_sink
> > > tmc_etr_sink_ops = {
> > >    const struct coresight_ops tmc_etr_cs_ops = {
> > >          .sink_ops       = &tmc_etr_sink_ops,
> > >    };
> > > +
> > > +int tmc_read_prepare_etr(struct tmc_drvdata *drvdata)
> > > +{
> > > +       unsigned long flags;
> > > +
> > > +       /* config types are set a boot time and never change */
> > > +       if (drvdata->config_type != TMC_CONFIG_TYPE_ETR)
> > > +               return -EINVAL;
> >
> >
> > ...
> >
> > > +
> > > +int tmc_read_unprepare_etr(struct tmc_drvdata *drvdata)
> > > +{
> > > +       unsigned long flags;
> > > +
> > > +       /* config types are set a boot time and never change */
> > > +       if (drvdata->config_type != TMC_CONFIG_TYPE_ETR)
> > > +               return -EINVAL;
> > > +
> >
> >
> > For both cases above should we WARN_ON_ONCE() if we encounter such a case ?
>
> WARN_ON_ONCE() would also be valid, albeit very blunt.  Those
> functions are user space triggered and returning -EINVAL will stop
> everything - the end result is the same.  I suppose that on such
> condition fighting back with a backtrace will force people to pay
> attention or report the problem.

We do necessary checks to route the caller here, so we shouldn't really
hit the condition with the tmc_read_prepare(). So WARN_ON_ONCE() might be a
good check to make sure we don't hit it from say, perf driver or something
really went bad under the hood (corrupted ?). I am not too particular about it.

Suzuki