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

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Date:   Mon, 4 Jan 2021 11:15:49 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     Rob Herring <robh@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.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 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.

> 
> That said, I am happy to move this under the CPU, if Mathieu is happy with
> the diversion.
> 
> Thanks for the review.
> 
> Suzuki