Re: [PATCH v2 12/17] coresight: trbe: Add a helper to fetch cpudata from perf handle

[Suzuki K Poulose]

On 06/10/2021 18:15, Mathieu Poirier wrote:
> On Tue, Oct 05, 2021 at 11:35:13PM +0100, Suzuki K Poulose wrote:
> > Hi Mathieu
> >
> > On 04/10/2021 18:42, Mathieu Poirier wrote:
> > > On Tue, Sep 21, 2021 at 02:41:16PM +0100, Suzuki K Poulose wrote:
> > > > Add a helper to get the CPU specific data for TRBE instance, from
> > > > a given perf handle. This also adds extra checks to make sure that
> > > > the event associated with the handle is "bound" to the CPU and is
> > > > active on the TRBE.
> > > >
> > > > Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> > > > Cc: Mike Leach <mike.leach@xxxxxxxxxx>
> > > > Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> > > > Cc: Leo Yan <leo.yan@xxxxxxxxxx>
> > > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > > > ---
> > > >    drivers/hwtracing/coresight/coresight-trbe.c | 12 ++++++++++--
> > > >    1 file changed, 10 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> > > > index 983dd5039e52..797d978f9fa7 100644
> > > > --- a/drivers/hwtracing/coresight/coresight-trbe.c
> > > > +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> > > > @@ -268,6 +268,15 @@ static unsigned long trbe_snapshot_offset(struct perf_output_handle *handle)
> > > >    	return buf->nr_pages * PAGE_SIZE;
> > > >    }
> > > > +static inline struct trbe_cpudata *
> > > > +trbe_handle_to_cpudata(struct perf_output_handle *handle)
> > > > +{
> > > > +	struct trbe_buf *buf = etm_perf_sink_config(handle);
> > > > +
> > > > +	BUG_ON(!buf || !buf->cpudata);
> > > > +	return buf->cpudata;
> > > > +}
> > > > +
> > > >    /*
> > > >     * TRBE Limit Calculation
> > > >     *
> > > > @@ -533,8 +542,7 @@ static enum trbe_fault_action trbe_get_fault_act(struct perf_output_handle *hand
> > > >    {
> > > >    	int ec = get_trbe_ec(trbsr);
> > > >    	int bsc = get_trbe_bsc(trbsr);
> > > > -	struct trbe_buf *buf = etm_perf_sink_config(handle);
> > > > -	struct trbe_cpudata *cpudata = buf->cpudata;
> > > > +	struct trbe_cpudata *cpudata = trbe_handle_to_cpudata(handle);
> > >
> > > There is two other places where this pattern is present:  is_perf_trbe() and
> > > __trbe_normal_offset().
> >
> > I skipped them, as they have to get access to the "trbe_buf" anyways.
> > So the step by step, made sense. But I could replace them too to make it
> > transparent.
> >
> > What do you think ?
>
> Humm...  I don't think there is a right way or a wrong way here.  If we move
> forward with this patchset we have two ways of getting to buf->cpudata.  One
> using trbe_handle_to_cpudata() and another one as laid out in is_perf_trbe() and
> __trbe_normal_offset(), each with an equal number of occurences (2 for each).
>
> I am usually not fond of small functions like trbe_handle_to_cpudata() and to me
> keeping the current heuristic in trbe_get_fault_act() would have been just fine.

There is another user introduced in the work around patch. But, yes, I
agree, we could open code it, rather than having it inconsistent across
the driver.

> I agree with the argument that trbe_handle_to_cpudata() provides more checks but
> is it really worth it if they aren't done everywhere?
>
> In short I would get rid of trbe_handle_to_cpudata() entirely and live without
> the extra checks... But I'm not strongly opinionated on this either.

Ok, I will remove this then. Thanks for the feedback.

Suzuki