Re: [PATCH V3 13/18] coresight: tmc: make sysFS and Perf mode mutually exclusive

[Suzuki K Poulose]

On 25/04/16 16:05, Mathieu Poirier wrote:
> On 25 April 2016 at 08:52, Suzuki K Poulose <Suzuki.Poulose@xxxxxxx> wrote:
> > On 25/04/16 15:48, Mathieu Poirier wrote:
> > > On 25 April 2016 at 08:32, Suzuki K Poulose <Suzuki.Poulose@xxxxxxx>
> > > wrote:
> > > > On 22/04/16 18:14, Mathieu Poirier wrote:
> >
> >
> > > > > +       spin_lock_irqsave(&drvdata->spinlock, flags);
> > > > > +       if (drvdata->reading) {
> > > > > +               ret = -EINVAL;
> > > > > +               goto out;
> > > > > +       }
> > > > > +
> > > > > +       val = local_xchg(&drvdata->mode, mode);
> > > > > +       /*
> > > > > +        * In Perf mode there can be only one writer per sink.  There
> > > > > +        * is also no need to continue if the ETR is already operated
> > > > > +        * from sysFS.
> > > > > +        */
> > > > > +       if (val != CS_MODE_DISABLED) {
> > > >
> > > >
> > > >
> > > > Could val be CS_MODE_PERF ? In other words, should we be checking :
> > > >           if (val == CS_MODE_SYSFS)  instead ?
> > >
> > >
> > > If we check for CS_MODE_SYSFS we also have to check for CS_MODE_PERF,
> > > which is two checks rather than a single one with the current
> > > solution.
> >
> >
> > I am confused now. The comment says, we want to check for sysfs mode and
> > don't continue in that case. So, we shouldn't be worried about PERF mode.
>
> You are correct about the sysFS part, but the first sentence of the
> comment also mention that in perf mode there can only be one writer
> per sink.  Otherwise ring buffers for one session would end up with
> traces from other ongoing sessions, and that is not taking into
> account the buffer management nightmares it would cause.

OK, in either case, val == CS_MODE_SYSFS is much better check there, to
what we want to do

Suzuki