Introduction

Architecture

The OTP driver follows Linux NVMEM framework, controls the firmware OTP controller, and performs the write and read of OTP. The OTP software architecture is illustrated in figure below.

../../_images/otp_software_arch.svg

OTP software architecture

The OTP driver provides the following two ways to control the hardware OTP device:

  • For user space, Linux NVMEM framework provides sysfs device for users to read and write.

  • For kernel space, Linux driver can control OTP device through NVMEM cell functions.

Implementation

The OTP driver is implemented as following files:

Driver location

Introduction

<linux>/drivers/rtkdrivers/otp/Kconfig

OTP driver Kconfig

<linux>/drivers/rtkdrivers/otp/Makefile

OTP driver Makefile

<linux>/drivers/rtkdrivers/otp/rtk-otp.c

OTP driver source code.

Configuration

Build Configuration: Select Device Drivers > Drivers for Realtek > NVMEM OTP driver.

../../_images/otp_driver.png

OTP driver

APIs

APIs for User Space

Just as mentioned above, Linux NVMEM framework provides sysfs device for user space to control the OTP device. Currently Realtek’s OTP driver provides two sysfs interfaces (/sys/bus/nvmem/devices/otp_raw0/nvmem and /sys/bus/nvmem/devices/otp_map0/nvmem) for user space to control the OTP device.

  • otp_raw0 device controls the physical map.

  • otp_map0 device controls the logical map.

The usage of demo is listed below:

efuse rraw/rmap [addr hex] [bytes]
efuse wraw/wmap [addr hex] [bytes] [val hex]

For example:

  • Read value from physical address 0x07F4 ~ 0x07F8:

    efuse rraw 7F4 4

  • Write the new value 0x021b1c1d to logical address 0x01e0 ~ 0x01e4:

    efuse wmap 1e0 4 021b1c1d

Refer to sources/development/cmds/efuse/efuse.c for more details.

If you want to disable APIs for user space, disable sysfs interface in kernel config as below:

../../_images/sysfs_interface1.png

Sysfs interface

APIs for Kernel Space

For kernel space, NVMEM provides cell mechanism for other drivers to read or write the OTP, such as:

../../_images/nvmem_cell_example.png

Nvmem-cell example

Drivers can use NVMEM cell functions to get or set the corresponding OTP values.