From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rob Herring Subject: Re: [PATCH v2 10/27] dts: bindings: Restrict coresight tmc-etr scatter-gather mode Date: Tue, 1 May 2018 08:13:00 -0500 Message-ID: <20180501131300.GA31425@rob-hp-laptop> References: <1525165857-11096-1-git-send-email-suzuki.poulose@arm.com> <1525165857-11096-11-git-send-email-suzuki.poulose@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1525165857-11096-11-git-send-email-suzuki.poulose@arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Suzuki K Poulose Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, mathieu.poirier@linaro.org, mike.leach@linaro.org, robert.walker@arm.com, mark.rutland@arm.com, will.deacon@arm.com, robin.murphy@arm.com, sudeep.holla@arm.com, frowand.list@gmail.com, john.horley@arm.com, Mathieu Poirier , devicetree@vger.kernel.org List-Id: devicetree@vger.kernel.org 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 > Cc: Mike Leach > Cc: Mark Rutland > Cc: John Horley > Cc: Robert Walker > Cc: devicetree@vger.kernel.org > Cc: frowand.list@gmail.com > Cc: Rob Herring > Signed-off-by: Suzuki K Poulose > --- > 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