linux-kernel - Re: [PATCH 06/11] dts: bindings: Document device tree bindings for ETE

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Message-ID: <CAL_Jsq+oBrfZrJAcg40gScAi2X4XTaskKD=qk+QvacYY=NTr7w@mail.gmail.com>
Date:   Mon, 4 Jan 2021 13:31:24 -0700
From:   Rob Herring <robh@...nel.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Coresight ML <coresight@...ts.linaro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mike Leach <mike.leach@...aro.org>,
        Linu Cherian <lcherian@...vell.com>, devicetree@...r.kernel.org
Subject: Re: [PATCH 06/11] dts: bindings: Document device tree bindings for ETE

On Mon, Jan 4, 2021 at 11:15 AM Mathieu Poirier
<mathieu.poirier@...aro.org> wrote:
>
> On Mon, Jan 04, 2021 at 02:42:08PM +0000, Suzuki K Poulose wrote:
> > Hi Rob,
> >
> > On 1/3/21 5:02 PM, Rob Herring wrote:
> > > On Wed, Dec 23, 2020 at 03:33:38PM +0530, Anshuman Khandual wrote:
> > > > From: Suzuki K Poulose <suzuki.poulose@....com>
> > > >
> > > > Document the device tree bindings for Embedded Trace Extensions.
> > > > ETE can be connected to legacy coresight components and thus
> > > > could optionally contain a connection graph as described by
> > > > the CoreSight bindings.
> > > >
> > > > Cc: devicetree@...r.kernel.org
> > > > Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> > > > Cc: Mike Leach <mike.leach@...aro.org>
> > > > Cc: Rob Herring <robh@...nel.org>
> > > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> > > > Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> > > > ---
> > > >   Documentation/devicetree/bindings/arm/ete.txt | 41 +++++++++++++++++++++++++++
> > > >   1 file changed, 41 insertions(+)
> > > >   create mode 100644 Documentation/devicetree/bindings/arm/ete.txt
> > >
> > > Bindings are in schema format now, please convert this.
> > >
> >
> > Sure, will do that.
> >
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/arm/ete.txt b/Documentation/devicetree/bindings/arm/ete.txt
> > > > new file mode 100644
> > > > index 0000000..b52b507
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/arm/ete.txt
> > > > @@ -0,0 +1,41 @@
> > > > +Arm Embedded Trace Extensions
> > > > +
> > > > +Arm Embedded Trace Extensions (ETE) is a per CPU trace component that
> > > > +allows tracing the CPU execution. It overlaps with the CoreSight ETMv4
> > > > +architecture and has extended support for future architecture changes.
> > > > +The trace generated by the ETE could be stored via legacy CoreSight
> > > > +components (e.g, TMC-ETR) or other means (e.g, using a per CPU buffer
> > > > +Arm Trace Buffer Extension (TRBE)). Since the ETE can be connected to
> > > > +legacy CoreSight components, a node must be listed per instance, along
> > > > +with any optional connection graph as per the coresight bindings.
> > > > +See bindings/arm/coresight.txt.
> > > > +
> > > > +** ETE Required properties:
> > > > +
> > > > +- compatible : should be one of:
> > > > + "arm,embedded-trace-extensions"
> > > > +
> > > > +- cpu : the CPU phandle this ETE belongs to.
> > >
> > > If this is 1:1 with CPUs, then perhaps it should be a child node of the
> > > CPU nodes.
> >
> > Yes, it is 1:1 with the CPUs. I have tried to keep this aligned with that of
> > "coresight-etm4x". The same driver handles both. The only reason why this
> > was separated from the "coresight.txt" is to describe the new configurations
> > possible (read, TRBE).
>
> Would it be possible to keep the CPU handle rather than moving things under the
> CPU nodes?  ETMv3.x and ETMv4.x are using a handle and as Suzuki points out ETE
> and ETMv4.x are sharing the same driver.  Proceeding differently for the ETE
> would be terribly confusing.

Yeah, no problem.

Rob