linux-kernel - Re: [PATCH v8 14/14] arm64: dts: qcom: Add EL2 overlay for Lemans

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Message-ID: <20251208142149.o6mmb7zwwjy7ywda@hu-mojha-hyd.qualcomm.com>
Date: Mon, 8 Dec 2025 19:51:49 +0530
From: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Mathieu Poirier <mathieu.poirier@...aro.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-remoteproc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 14/14] arm64: dts: qcom: Add EL2 overlay for Lemans

On Fri, Dec 05, 2025 at 05:00:20PM -0600, Bjorn Andersson wrote:
> On Fri, Nov 21, 2025 at 04:31:16PM +0530, Mukesh Ojha wrote:
> > All the Lemans IOT variants boards are using Gunyah hypervisor which
> > means that, so far, Linux-based OS could only boot in EL1 on those
> > devices.  However, it is possible for us to boot Linux at EL2 on these
> > devices [1].
> > 
> > When running under Gunyah, remote processor firmware IOMMU streams is
> > controlled by the Gunyah however when Linux take ownership of it in EL2,
> > It need to configure it properly to use remote processor.
> > 
> > Add a EL2-specific DT overlay and apply it to Lemans IOT variant
> > devices to create -el2.dtb for each of them alongside "normal" dtb.
> > 
> > [1]
> > https://docs.qualcomm.com/bundle/publicresource/topics/80-70020-4/boot-developer-touchpoints.html#uefi
> > 
> > Signed-off-by: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
> > ---
> >  arch/arm64/boot/dts/qcom/Makefile        | 10 ++++++++
> >  arch/arm64/boot/dts/qcom/lemans-el2.dtso | 41 ++++++++++++++++++++++++++++++++
> >  2 files changed, 51 insertions(+)
> > 
> > diff --git a/arch/arm64/boot/dts/qcom/Makefile b/arch/arm64/boot/dts/qcom/Makefile
> > index 6f34d5ed331c..56efd90b7a5e 100644
> > --- a/arch/arm64/boot/dts/qcom/Makefile
> > +++ b/arch/arm64/boot/dts/qcom/Makefile
> > @@ -37,6 +37,10 @@ lemans-evk-camera-dtbs	:= lemans-evk.dtb lemans-evk-camera.dtbo
> >  
> >  dtb-$(CONFIG_ARCH_QCOM)	+= lemans-evk-camera-csi1-imx577.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)	+= lemans-evk-camera.dtb
> > +
> > +lemans-evk-el2-dtbs := lemans-evk.dtb lemans-el2.dtbo
> > +
> > +dtb-$(CONFIG_ARCH_QCOM)	+= lemans-evk-el2.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)	+= monaco-evk.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)	+= msm8216-samsung-fortuna3g.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)	+= msm8916-acer-a1-724.dtb
> > @@ -142,6 +146,12 @@ dtb-$(CONFIG_ARCH_QCOM)	+= qcs8300-ride.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)	+= qcs8550-aim300-aiot.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)	+= qcs9100-ride.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)	+= qcs9100-ride-r3.dtb
> > +
> > +qcs9100-ride-el2-dtbs := qcs9100-ride.dtb lemans-el2.dtbo
> > +qcs9100-ride-r3-el2-dtbs := qcs9100-ride-r3.dtb lemans-el2.dtbo
> > +
> > +dtb-$(CONFIG_ARCH_QCOM)	+= qcs9100-ride-el2.dtb
> > +dtb-$(CONFIG_ARCH_QCOM)	+= qcs9100-ride-r3-el2.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)	+= qdu1000-idp.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)	+= qrb2210-rb1.dtb
> >  dtb-$(CONFIG_ARCH_QCOM)	+= qrb4210-rb2.dtb
> > diff --git a/arch/arm64/boot/dts/qcom/lemans-el2.dtso b/arch/arm64/boot/dts/qcom/lemans-el2.dtso
> > new file mode 100644
> > index 000000000000..af35039946e3
> > --- /dev/null
> > +++ b/arch/arm64/boot/dts/qcom/lemans-el2.dtso
> > @@ -0,0 +1,41 @@
> > +// SPDX-License-Identifier: BSD-3-Clause
> > +/*
> > + * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
> > + */
> > +
> > +/*
> > + * Lemans specific modifications required to boot in EL2.
> > + */
> > +
> > +/dts-v1/;
> > +/plugin/;
> > +
> > +&iris {
> > +	/* More driver work is needed */
> 
> You can write this comment without referring to some particular
> implementation (as DeviceTree should).
> 
> /* The binding doesn't allow for describing the firmware IOMMU stream yet */
> 
> > +	status = "disabled";
> > +};
> > +
> > +/*
> > + * When running under Gunyah, remote processor firmware IOMMU streams is
> > + * controlled by the Gunyah however when we take ownership of it in EL2,
> > + * we need to configure it properly to use remote processor.
> 
> The comment describes how things work with Gunyah, and then from that
> angle explains why we need this. I'd find it preferable to keep the
> perspective of not having Gunyah. Something as simple as:
> 
> /*
>  * Without Gunyah, the IOMMU is managed by the consumer of this DeviceTree,
>  * so describe the firmware streams for each remoteproc.
>  */
> 
> That said, once the iris binding (and others) allow us to describe the
> firmware stream, this comment will be misplaced. So perhaps apply my
> feedback to the commit message and omit the comment here. If someone
> wonders why it looks like it does, the commit message in the git history
> will tell them.

Will move all the required comments into description of commit message.

-- 
-Mukesh Ojha