linux-kernel - Re: [PATCH v4 01/10] dt-bindings: soc: google: add google,gs101-dtzpc

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Message-ID: <74eb8fb542966c46d0a8c77041aeef21dd1a7e14.camel@linaro.org>
Date: Fri, 30 Jan 2026 05:40:13 +0000
From: André Draszik <andre.draszik@...aro.org>
To: Rob Herring <robh@...nel.org>
Cc: Krzysztof Kozlowski <krzk@...nel.org>, Alim Akhtar
 <alim.akhtar@...sung.com>,  Conor Dooley <conor+dt@...nel.org>, Krzysztof
 Kozlowski <krzk+dt@...nel.org>, Ulf Hansson	 <ulf.hansson@...aro.org>, Liam
 Girdwood <lgirdwood@...il.com>, Mark Brown	 <broonie@...nel.org>, Peter
 Griffin <peter.griffin@...aro.org>, Tudor Ambarus	
 <tudor.ambarus@...aro.org>, Juan Yescas <jyescas@...gle.com>, Will McVicker
	 <willmcvicker@...gle.com>, kernel-team@...roid.com, 
	linux-arm-kernel@...ts.infradead.org, linux-samsung-soc@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org
Subject: Re: [PATCH v4 01/10] dt-bindings: soc: google: add
 google,gs101-dtzpc

Hi Rob,

On Thu, 2026-01-29 at 10:55 -0600, Rob Herring wrote:
> On Wed, Jan 28, 2026 at 04:10:50PM +0000, André Draszik wrote:
> > The Exynos Distributed TruztZone Protection Control (D_TZPC) provides
> > an interface to the protection bits that are included in the TrustZone
> > design in a secure system. It configures each area of the memory as
> > secure or non-secure.
> 
> This sounds like what access-controllers binding is for. Does that work 
> here?

Thank you for the pointer, and yes, I did consider it, but decided against
it in the end for the following reasons:

* downstream drivers don't actually do much with this, it's only used to
  issue a request to the firmware to save / restore the configuration
  when power domains are turned off / on (via SMC call). There is no
  actual configuration happening unlike e.g. the drivers/bus/stm32_*
  case. Configuration etc. seems to be handled statically in the firmware
  in my case.

* therefore I didn't write an actual driver for this compatible and my
  patches are proposing to simply issue the SMC from the power domain
  driver in the respective paths.
  What I observed without having a driver matching the compatible, Linux
  will defer binding of consumer drivers (power domain via phandle in my
  case) until the access controller driver has bound. Since no such driver
  exists in my case, Linux keeps deferring the binding of my power domain
  driver forever, meaning it doesn't probe.

Maybe this restriction could be loosened for cases like this instead. Or
maybe I do need to write a dtzpc driver with the only purpose to issue the
SMC calls at the right time. Having such a driver seemed like overkill,
though.

I realise not using access-controller in DT looks like working-around an
issue in the kernel, but due to the minimal interaction from the Linux-side
I was hoping for that to be OK.

What do you think?


Cheers,
Andre'

> 
> > Signed-off-by: André Draszik <andre.draszik@...aro.org>
> > ---
> >  .../bindings/soc/google/google,gs101-dtzpc.yaml    | 42 ++++++++++++++++++++++
> >  MAINTAINERS                                        |  1 +
> >  2 files changed, 43 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/soc/google/google,gs101-dtzpc.yaml
> > b/Documentation/devicetree/bindings/soc/google/google,gs101-dtzpc.yaml
> > new file mode 100644
> > index 0000000000000000000000000000000000000000..a8c61ce069d6910c47753bf14a792eb58e6ae182
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/soc/google/google,gs101-dtzpc.yaml
> > @@ -0,0 +1,42 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/soc/google/google,gs101-dtzpc.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Samsung Exynos Distributed TruztZone Protection Control.
> > +
> > +description:
> > +  Distributed TrustZone Protection Control (D_TZPC) provides an interface to the
> > +  protection bits that are included in the TrustZone design in a secure system.
> > +  It configures each area of the memory as secure or non-secure.
> > +
> > +maintainers:
> > +  - André Draszik <andre.draszik@...aro.org>
> > +
> > +properties:
> > +  compatible:
> > +    const: google,gs101-dtzpc
> > +
> > +  clocks:
> > +    maxItems: 1
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +required:
> > +  - compatible
> > +  - clocks
> > +  - reg
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    #include <dt-bindings/clock/google,gs101.h>
> > +
> > +    dtzpc_hsi0: dtzpc@...10000 {
> > +      compatible = "google,gs101-dtzpc";
> > +      reg = <0x11010000 0x10000>;
> > +      clocks = <&cmu_hsi0 CLK_GOUT_HSI0_D_TZPC_HSI0_PCLK>;
> > +    };
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index a56f8f00aebb938aa765a8a6d66dfeb7f062dac8..98b2ef47c809ac0232e6941c9483b19d7c798bb4 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -10833,6 +10833,7 @@ P:	Documentation/process/maintainer-soc-clean-dts.rst
> >  C:	irc://irc.oftc.net/pixel6-kernel-dev
> >  F:	Documentation/devicetree/bindings/clock/google,gs101-clock.yaml
> >  F:	Documentation/devicetree/bindings/phy/google,lga-usb-phy.yaml
> > +F:	Documentation/devicetree/bindings/soc/google/google,gs101-dtzpc.yaml
> >  F:	Documentation/devicetree/bindings/soc/google/google,gs101-pmu-intr-gen.yaml
> >  F:	Documentation/devicetree/bindings/usb/google,lga-dwc3.yaml
> >  F:	arch/arm64/boot/dts/exynos/google/
> > 
> > -- 
> > 2.52.0.457.g6b5491de43-goog
> >