Re: [PATCH v2 03/17] coresight: trbe: Add a helper to calculate the trace generated

[Suzuki K Poulose]

On 01/10/2021 16:15, Mathieu Poirier wrote:
> On Fri, Oct 01, 2021 at 09:36:24AM +0100, Suzuki K Poulose wrote:
> > On 30/09/2021 18:54, Mathieu Poirier wrote:
> > > Hi Suzuki,
> > >
> > > On Tue, Sep 21, 2021 at 02:41:07PM +0100, Suzuki K Poulose wrote:
> > > > We collect the trace from the TRBE on FILL event from IRQ context
> > > > and when via update_buffer(), when the event is stopped. Let us
> > >
> > > s/"and when via"/"and via"
> > >
> > > > consolidate how we calculate the trace generated into a helper.
> > > >
> > > > Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> > > > Cc: Mike Leach <mike.leach@xxxxxxxxxx>
> > > > Cc: Leo Yan <leo.yan@xxxxxxxxxx>
> > > > Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> > > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > > > ---
> > > >    drivers/hwtracing/coresight/coresight-trbe.c | 48 ++++++++++++--------
> > > >    1 file changed, 30 insertions(+), 18 deletions(-)
> > > >
> > > > diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> > > > index 63f7edd5fd1f..063c4505a203 100644
> > > > --- a/drivers/hwtracing/coresight/coresight-trbe.c
> > > > +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> > > > @@ -527,6 +527,30 @@ static enum trbe_fault_action trbe_get_fault_act(u64 trbsr)
> > > >    	return TRBE_FAULT_ACT_SPURIOUS;
> > > >    }
> > > > +static unsigned long trbe_get_trace_size(struct perf_output_handle *handle,
> > > > +					 struct trbe_buf *buf,
> > > > +					 bool wrap)
> > >
> > > Stacking
> >
> > Ack
> >
> > > > +{
> > > > +	u64 write;
> > > > +	u64 start_off, end_off;
> > > > +
> > > > +	/*
> > > > +	 * If the TRBE has wrapped around the write pointer has
> > > > +	 * wrapped and should be treated as limit.
> > > > +	 */
> > > > +	if (wrap)
> > > > +		write = get_trbe_limit_pointer();
> > > > +	else
> > > > +		write = get_trbe_write_pointer();
> > > > +
> > > > +	end_off = write - buf->trbe_base;
> > >
> > > In both arm_trbe_alloc_buffer() and trbe_handle_overflow() the base address is
> > > acquired using get_trbe_base_pointer() but here it is referenced directly - any
> > > reason for that?  It certainly makes reviewing this simple patch quite
> > > difficult because I keep wondering if I am missing something subtle...
> >
> > Very good observation. So far, we always prgrammed the TRBBASER with the
> > the VA(ring_buffer[0]). And thus reading the BASER and using the
> > buf->trbe_base is all fine.
> >
> > But going forward, we are going to use different values for the TRBBASER
> > to work around erratum. Thus to make the computation of the "offsets"
> > within the ring buffer, it is always correct to use this field. I could
> > move this to the patch where the work around is introduced, and put in
> > a comment there.
>
> That will be greatly appreciated.

I have moved this to the patch, which introduces the concept of "TRBE 
using" a different BASE address than the beginning of the ring buffer.

Thanks
Suzuki