Re: [PATCH v19 4/6] dt-bindings: remoteproc: Add compatibility for TEE support

Sumit Garg
2025-09-16T09:14:57Z

Hi Arnaud,

First of all apologies for such a late review comment as previously I
wasn't CCed or involved in the review of this patch-set. In case any of
my following comments have been discussed in the past then feel free to
point me at relevant discussions.

On Wed, Jun 25, 2025 at 11:40:26AM +0200, Arnaud Pouliquen wrote:
> The "st,stm32mp1-m4-tee" compatible is utilized in a system configuration
> where the Cortex-M4 firmware is loaded by the Trusted Execution Environment
> (TEE).

Having a DT based compatible for a TEE service to me just feels like it
is redundant here. I can see you have also used a TEE bus based device
too but that is not being properly used. I know subsystems like
remoteproc, SCMI and others heavily rely on DT to hardcode properties of
system firmware which are rather better to be discovered dynamically.

So I have an open question for you and the remoteproc subsystem
maintainers being:

Is it feasible to rather leverage the benefits of a fully discoverable
TEE bus rather than relying on platform bus/ DT to hardcode firmware
properties?

>
> For instance, this compatible is used in both the Linux and OP-TEE device
> trees:
> - In OP-TEE, a node is defined in the device tree with the
> "st,stm32mp1-m4-tee" compatible to support signed remoteproc firmware.
> Based on DT properties, the OP-TEE remoteproc framework is initiated to
> expose a trusted application service to authenticate and load the remote
> processor firmware provided by the Linux remoteproc framework, as well
> as to start and stop the remote processor.
> - In Linux, when the compatibility is set, the Cortex-M resets should not
> be declared in the device tree. In such a configuration, the reset is
> managed by the OP-TEE remoteproc driver and is no longer accessible from
> the Linux kernel.
>
> Associated with this new compatible, add the "st,proc-id" property to
> identify the remote processor. This ID is used to define a unique ID,
> common between Linux, U-Boot, and OP-TEE, to identify a coprocessor.

This "st,proc-id" is just one such property which can rather be directly
probed from the TEE/OP-TEE service rather than hardcoding it in DT here.
I think the same will apply to other properties as well.

-Sumit

> This ID will be used in requests to the OP-TEE remoteproc Trusted
> Application to specify the remote processor.
>
> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
> Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
> ---
> .../bindings/remoteproc/st,stm32-rproc.yaml | 58 ++++++++++++++++---
> 1 file changed, 50 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/remoteproc/st,stm32-rproc.yaml b/Documentation/devicetree/bindings/remoteproc/st,stm32-rproc.yaml
> index 843679c557e7..58da07e536fc 100644
> --- a/Documentation/devicetree/bindings/remoteproc/st,stm32-rproc.yaml
> +++ b/Documentation/devicetree/bindings/remoteproc/st,stm32-rproc.yaml
> @@ -16,7 +16,12 @@ maintainers:
>
> properties:
> compatible:
> - const: st,stm32mp1-m4
> + enum:
> + - st,stm32mp1-m4
> + - st,stm32mp1-m4-tee
> + description:
> + Use "st,stm32mp1-m4" for the Cortex-M4 coprocessor management by non-secure context
> + Use "st,stm32mp1-m4-tee" for the Cortex-M4 coprocessor management by secure context
>
> reg:
> description:
> @@ -43,6 +48,10 @@ properties:
> - description: The offset of the hold boot setting register
> - description: The field mask of the hold boot
>
> + st,proc-id:
> + description: remote processor identifier
> + $ref: /schemas/types.yaml#/definitions/uint32
> +
> st,syscfg-tz:
> deprecated: true
> description:
> @@ -146,21 +155,43 @@ properties:
> required:
> - compatible
> - reg
> - - resets
>
> allOf:
> - if:
> properties:
> - reset-names:
> - not:
> - contains:
> - const: hold_boot
> + compatible:
> + contains:
> + const: st,stm32mp1-m4
> then:
> + if:
> + properties:
> + reset-names:
> + not:
> + contains:
> + const: hold_boot
> + then:
> + required:
> + - st,syscfg-holdboot
> + else:
> + properties:
> + st,syscfg-holdboot: false
> + required:
> + - reset-names
> required:
> - - st,syscfg-holdboot
> - else:
> + - resets
> +
> + - if:
> + properties:
> + compatible:
> + contains:
> + const: st,stm32mp1-m4-tee
> + then:
> properties:
> st,syscfg-holdboot: false
> + reset-names: false
> + resets: false
> + required:
> + - st,proc-id
>
> additionalProperties: false
>
> @@ -192,5 +223,16 @@ examples:
> st,syscfg-rsc-tbl = <&tamp 0x144 0xFFFFFFFF>;
> st,syscfg-m4-state = <&tamp 0x148 0xFFFFFFFF>;
> };
> + - |
> + #include <dt-bindings/reset/stm32mp1-resets.h>
> + m4@10000000 {
> + compatible = "st,stm32mp1-m4-tee";
> + reg = <0x10000000 0x40000>,
> + <0x30000000 0x40000>,
> + <0x38000000 0x10000>;
> + st,proc-id = <0>;
> + st,syscfg-rsc-tbl = <&tamp 0x144 0xFFFFFFFF>;
> + st,syscfg-m4-state = <&tamp 0x148 0xFFFFFFFF>;
> + };
>
> ...
> --
> 2.25.1
>
>