On Tue, May 01, 2018 at 10:10:40AM +0100, Suzuki K Poulose wrote: > We are about to add the support for ETR builtin scatter-gather mode > for dealing with large amount of trace buffers. However, on some of > the platforms, using the ETR SG mode can lock up the system due to > the way the ETR is connected to the memory subsystem. > > In SG mode, the ETR performs READ from the scatter-gather table to > fetch the next page and regular WRITE of trace data. If the READ > operation doesn't complete(due to the memory subsystem issues, > which we have seen on a couple of platforms) the trace WRITE > cannot proceed leading to issues. So, we by default do not > use the SG mode, unless it is known to be safe on the platform. > We define a DT property for the TMC node to specify whether we > have a proper SG mode. > > Cc: Mathieu Poirier <matheiu.poir...@linaro.org> > Cc: Mike Leach <mike.le...@linaro.org> > Cc: Mark Rutland <mark.rutl...@arm.com> > Cc: John Horley <john.hor...@arm.com> > Cc: Robert Walker <robert.wal...@arm.com> > Cc: devicet...@vger.kernel.org > Cc: frowand.l...@gmail.com > Cc: Rob Herring <r...@kernel.org> > Signed-off-by: Suzuki K Poulose <suzuki.poul...@arm.com> > --- > Documentation/devicetree/bindings/arm/coresight.txt | 3 +++ > drivers/hwtracing/coresight/coresight-tmc.c | 8 +++++++- > 2 files changed, 10 insertions(+), 1 deletion(-) > > diff --git a/Documentation/devicetree/bindings/arm/coresight.txt > b/Documentation/devicetree/bindings/arm/coresight.txt > index cdd84d0..7c0c8f0 100644 > --- a/Documentation/devicetree/bindings/arm/coresight.txt > +++ b/Documentation/devicetree/bindings/arm/coresight.txt > @@ -88,6 +88,9 @@ its hardware characteristcs. > * arm,buffer-size: size of contiguous buffer space for TMC ETR > (embedded trace router) > > + * scatter-gather: boolean. Indicates that the TMC-ETR can safely > + use the SG mode on this system. > +
Needs a vendor prefix. > * Optional property for CATU : > * interrupts : Exactly one SPI may be listed for reporting the address > error
