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BSEC device tree configuration: Difference between revisions

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<noinclude>{{ApplicableFor
{{ApplicableFor
|MPUs list=STM32MP13x, STM32MP15x
|MPUs list=STM32MP13x, STM32MP15x, STM32MP25x
|MPUs checklist=STM32MP13x,STM32MP15x
|MPUs checklist=STM32MP13x, STM32MP15x, STM32MP25x
}}</noinclude>
}}
<noinclude></noinclude>
== Article purpose ==
== 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.
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.
Line 39: Line 40:


   &bsec {
   &bsec {
  calib@20 {
  reg = <0x20 0x2>;
  };
   board_id: board_id@ec {
   board_id: board_id@ec {
   reg = <0xec 0x4>;
   reg = <0xec 0x4>;
   {{highlightParam|st,non-secure-otp}};
   {{highlightParam|st,non-secure-otp}};
  };
  oem_enc_key@170 {
  reg = <0x170 0x10>;
  {{highlightParam|st,non-secure-otp-provisioning}};
   };
   };
   };
   };


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/>
Only the 32 lower NVMEM 32-bit data words are accessible by the non-secure world by default; [[STM32 MPU OP-TEE_overview|OP-TEE]] needs to manage exceptions in [[OP-TEE_OTP_overview|BSEC PTA]] to allow some upper OTPs to be accessed by the non-secure world, through secure world services for very specific needs as described in {{CodeSource | OP-TEE_OS | documentation/devicetree/bindings/nvmem/st,stm32-romem.yaml}}.
 
{{Warning| These upper OTP 32-bit length words are ECC-protected. To avoid an invalid ECC, computed after a second write operation, these 64 upper OTPs should be be permanent write locked when they are programmed.}}
 
This exceptions are defined by the OTP declaration in the secure world device tree with a 32-bit length granularity (that is, 4 bytes):
* using the {{highlightParam|st,non-secure-otp}} property to allow a read/write
* using the {{highlightParam|st,non-secure-otp-provisioning}} property to allow a write until the first programmed value or permanent lock; used for secrets used by secure world but provisioned by the non-secured world.
 
See example {{CodeSource | OP-TEE_OS | core/arch/arm/dts/stm32mp135f-dk.dts}}.


==How to configure the DT using STM32CubeMX==
==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 />
The [[STM32CubeMX]] tool can be used to configure the STM32MPU device and get the corresponding [[Device_tree#STM32_MPU|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.
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.


Latest revision as of 16:02, 25 July 2024↑

Applicable for STM32MP13x lines, STM32MP15x lines, Unknown MPU

1. Article purpose↑

The purpose of this article is to explain how to configure the BSEC using the device tree mechanism, relying on the bindings documentation, that is the description of the required and optional device-tree properties.

2. DT bindings documentation↑

Generic information about NVMEM is available in the NVMEM overview.

The device tree binding documents for BSEC are stored either in the given applicable components listed below, or in the Linux kernel repository:

3. 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 for more details.

3.1. DT configuration (STM32/SoC level)↑

The BSEC node and NVMEM node are located in the device tree file for the software components, supporting the peripheral and listed in the above DT bindings documentation paragraph.

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

3.2. DT configuration (board level)↑

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

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

3.2.1. 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 {
 	calib@20 {
 		reg = <0x20 0x2>;
 	};
 	board_id: board_id@ec {
 		reg = <0xec 0x4>;
 		st,non-secure-otp;
 	};
 	oem_enc_key@170 {
 		reg = <0x170 0x10>;
 		st,non-secure-otp-provisioning;
 	};
 };

Only the 32 lower NVMEM 32-bit data words are accessible by the non-secure world by default; OP-TEE needs to manage exceptions in BSEC PTA to allow some upper OTPs to be accessed by the non-secure world, through secure world services for very specific needs as described in documentation/devicetree/bindings/nvmem/st,stm32-romem.yaml .

Warning white.png Warning
These upper OTP 32-bit length words are ECC-protected. To avoid an invalid ECC, computed after a second write operation, these 64 upper OTPs should be be permanent write locked when they are programmed.

This exceptions are defined by the OTP declaration in the secure world device tree with a 32-bit length granularity (that is, 4 bytes):

  • using the st,non-secure-otp property to allow a read/write
  • using the st,non-secure-otp-provisioning property to allow a write until the first programmed value or permanent lock; used for secrets used by secure world but provisioned by the non-secured world.

See example core/arch/arm/dts/stm32mp135f-dk.dts .

4. How to configure the DT using STM32CubeMX↑

The STM32CubeMX tool can be used to configure the STM32MPU device and get the corresponding platform configuration device tree files.
STM32CubeMX may not support all the properties described in DT binding files listed in the above 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.

5. References↑

Please refer to the following links for additional information:



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