linux-kernel - Re: [PATCH v3 1/2] dt-bindings: arm: Add Qualcomm extended CTI

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Message-ID: <CAJ9a7VhLLgAak_4FB=iW0izXprM4W+RsKfHUeo=XUHh9LwtUsA@mail.gmail.com>
Date: Tue, 22 Jul 2025 13:00:18 +0100
From: Mike Leach <mike.leach@...aro.org>
To: Leo Yan <leo.yan@....com>
Cc: Suzuki K Poulose <suzuki.poulose@....com>, Mao Jinlong <quic_jinlmao@...cinc.com>, 
	James Clark <james.clark@...aro.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Yingchao Deng <quic_yingdeng@...cinc.com>, coresight@...ts.linaro.org, 
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v3 1/2] dt-bindings: arm: Add Qualcomm extended CTI

Hi

On Tue, 22 Jul 2025 at 10:14, Leo Yan <leo.yan@....com> wrote:
>
> On Tue, Jul 22, 2025 at 09:49:28AM +0100, Suzuki Kuruppassery Poulose wrote:
> > On 22/07/2025 09:14, Mao Jinlong wrote:
> > > From: Yingchao Deng <quic_yingdeng@...cinc.com>
> > >
> > > Add Qualcomm extended CTI support in CTI binding file. Qualcomm
> > > extended CTI supports up to 128 triggers.
> > >
> > > Signed-off-by: Yingchao Deng <quic_yingdeng@...cinc.com>
> > > Signed-off-by: Mao Jinlong <quic_jinlmao@...cinc.com>
> > > ---
> > >   Documentation/devicetree/bindings/arm/arm,coresight-cti.yaml | 4 +++-
> > >   1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/Documentation/devicetree/bindings/arm/arm,coresight-cti.yaml b/Documentation/devicetree/bindings/arm/arm,coresight-cti.yaml
> > > index 2d5545a2b49c..1aa27461f5bc 100644
> > > --- a/Documentation/devicetree/bindings/arm/arm,coresight-cti.yaml
> > > +++ b/Documentation/devicetree/bindings/arm/arm,coresight-cti.yaml
> > > @@ -84,7 +84,9 @@ properties:
> > >             - const: arm,coresight-cti
> > >             - const: arm,primecell
> > >         - items:
> > > -          - const: arm,coresight-cti-v8-arch
> > > +          - enum:
> > > +              - arm,coresight-cti-v8-arch
> > > +              - qcom,coresight-cti-extended
> >
> > Why not call it qcom,coresight-cti ?
> >
> > There are no other "qcom,coresight-cti", so "extended" is not required.
> > Is this specific to CPU (i.e., CPU bound) ?
>
> I roughly went through the second path. Combining two patches in this
> series, I am wandering if can directly check registers (e.g. PID/CID)
> to find CTI with qcom extension. If so, you do not need an extra DT
> binding, right?
>
> Thanks,
> Leo
>
> > Suzuki
> >
> > >             - const: arm,coresight-cti
> > >             - const: arm,primecell
> >
> > _______________________________________________
> > CoreSight mailing list -- coresight@...ts.linaro.org
> > To unsubscribe send an email to coresight-leave@...ts.linaro.org

For a change of this magnitude to a CS component, that the ID
registers will also have to change. This is a requirement of the
Visible Component Architecture in the CoreSight specification.
External tools cannot see the device tree.

This is effectively no longer an ARM designed component, so the
CoreSight specification requires that the DEVARCH register change to
show qualcomm as the designer, and the architecture value change to
represent this component.
DEVID should be used to allow the driver to pick up parameters such as
number of triggers as per the existing CTI component.

If this component is Coresight compliant then the driver can use the
ID registers to configure to the extended trigger architecture.

With complete remapping of most of the registers, and the dropping of
claim tag compatibility - which appears to be a breach of the
CoreSight specification - it may be better to have a completely
separate driver for this component.

Regards


Mike

--
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK