View source for BSEC device tree configuration

<noinclude>{{ApplicableFor
|MPUs list=STM32MP13x, STM32MP15x
|MPUs checklist=STM32MP13x,STM32MP15x
}}</noinclude>
== Article purpose ==
The purpose of this article is to explain how to configure the [[BSEC internal peripheral|BSEC]] using the [[Device tree|device tree]] mechanism, relying on the bindings documentation, that is the description of the required and optional device-tree properties.

== DT bindings documentation ==

Generic information about NVMEM is available in the [[NVMEM_overview#Device_tree_configuration|NVMEM overview]].

The device tree binding documents for [[BSEC internal peripheral|BSEC]] are stored either in the given applicable components listed below, or in the Linux kernel repository:
* TF-A BL2: 
**for example: {{CodeSource | TF-A  | docs/devicetree/bindings/soc/st,stm32-romem.txt}}
* OP-TEE:
** for example: STM32 BSEC device tree bindings: {{CodeSource | OP-TEE_OS | documentation/devicetree/bindings/nvmem/st,stm32-romem.yaml}}
* U-Boot, Linux<sup>&reg;</sup> OS:
** for example: STM32 BSEC device tree bindings: {{CodeSource | Linux kernel | Documentation/devicetree/bindings/nvmem/st,stm32-romem.yaml}}
** for example: generic NVMEM devicetree bindings: {{CodeSource | Linux kernel | Documentation/devicetree/bindings/nvmem/nvmem.yaml}}, {{CodeSource | Linux kernel | Documentation/devicetree/bindings/nvmem/nvmem-consumer.yaml}}

== DT configuration ==
This hardware description is a combination of the '''STM32 microprocessor''' device tree files (''.dtsi'' extension) and '''board''' device tree files (''.dts'' extension). See the [[Device tree]] for an explanation of the device-tree file organization.

'''STM32CubeMX''' can be used to generate the board device tree. Refer to [[#How_to_configure_the_DT_using_STM32CubeMX|How to configure the DT using STM32CubeMX]] for more details.

=== DT configuration (STM32/SoC level) ===
The [[BSEC_internal_peripheral|BSEC]] node and [[NVMEM_overview#Device_tree_configuration|NVMEM]] node are located in the [[STM32 MPU device_tree#Device tree structure|device tree file]] for the software components, supporting the peripheral and listed in the above [[#DT bindings documentation|DT bindings documentation]] paragraph.

{{Warning|This device tree part is related to STM32 microprocessors. It must be kept as is, without being modified by the end-user.}}

=== DT configuration (board level) ===

The objective of this chapter is to explain how to enable and configure the  [[BSEC_internal_peripheral|BSEC]]  DT nodes for a board.

Peripheral configuration should be done in specific board device tree files (board dts file).

==== BSEC node append ====
The board definition in the device tree may include some additional board-specific OTP declarations, for example to add a NVMEM data cell:

  &bsec {
  	board_id: board_id@ec {
  		reg = <0xec 0x4>;
  		{{highlightParam|st,non-secure-otp}};
  	};
  };

With only 32 lower NVMEM 32-bit data words, the secure world software (OP-TEE or SP-MIN) needs to manage exceptions in order to allow some upper OTPs to be accessed by the non-secure world, through secure world services for very specific needs. The user can add an OTP declaration in the device tree, using the {{highlightParam|st,non-secure-otp}} property used in secure world device tree, with a 32-bit length granularity (that is, 4 bytes).<br/>

==How to configure the DT using STM32CubeMX==
The [[STM32CubeMX]] tool can be used to configure the STM32MPU device and get the corresponding [[Device_tree#STM32|platform configuration device tree]] files.<br />
STM32CubeMX may not support all the properties described in DT binding files listed in the above [[#DT bindings documentation|DT bindings documentation]] paragraph. If so, the tool inserts '''user sections''' in the generated device tree. These sections can then be edited to add some properties, and they are preserved from one generation to another. Refer to [[STM32CubeMX]] user manual for further information.

==References==
Please refer to the following links for additional information:

<references />
<noinclude>
[[Category:Device tree configuration]]
[[Category:OP-TEE Persistent storage]] 
{{ArticleBasedOnModel | Peripheral or framework device tree configuration model}}
{{PublicationRequestId | 15044 | 2020-02-21 | 13613 (PhilipS - 2019-10-09))}}
</noinclude>