The STM STM32MP15 CPU provides a set of one-time programmable bits (OTPs) structured as 3072 effective bits. The OTPs are accessed through 32-bit words.
Kernel configuration
You can manage the OTP driver support through the kernel configuration option:
-
STM32 factory-programmed memory support (
CONFIG_NVMEM_STM32_ROMEM)
This option is enabled as built-in on the ConnectCore MP15 default kernel configuration file.
Kernel driver
The memory driver is located at:
| File | Description |
|---|---|
STM32 factory-programmed memory support |
Device tree bindings
The STM32MP15 OTP memory driver device tree binding are documented at
File |
Description |
STM32 BSEC device tree binding |
|
Generic NVMEM device tree bindings |
|
Generic device tree bindings |
The STM32MP15 device tree include file defines the bsec node and inside it, a number of relevant OTP words.
bsec: efuse@5c005000 {
compatible = "st,stm32mp15-bsec";
reg = <0x5c005000 0x400>;
clocks = <&scmi_clk CK_SCMI_BSEC>;
#address-cells = <1>;
#size-cells = <1>;
part_number_otp: part_number_otp@4 {
reg = <0x4 0x1>;
};
vrefint: calib@52 {
reg = <0x52 0x2>;
};
ts_cal1: calib@5c {
reg = <0x5c 0x2>;
};
ts_cal2: calib@5e {
reg = <0x5e 0x2>;
};
ethernet_mac_address: mac@e4 {
reg = <0xe4 0x6>;
};
};OTP user space usage
The OTP words are accessible through the sysfs at /sys/bus/nvmem/devices/stm32-romem0/nvmem.
| It is not possible to write to OTP data with Linux driver; BSEC is defined as a read-only NVMEM device. This is done to prevent accidentally programming the OTP bits. |
Read the OTP bits
To dump the values of all OTP words:
# hexdump -e '"%08_ax: " 4/4 "%08x " "\n"' /sys/bus/nvmem/devices/stm32-romem0/nvmem
00000000: 00000017 00008000 a0200000 00000000
00000010: 00000000 00000000 00000000 00000000
*
00000030: 7cf5f917 00360035 32315117 32393532
00000040: 139685e7 20eb0868 7c3f0140 06be143d
00000050: 5da5003b 00000000 00000000 3f992fe9
00000060: 00000000 00000000 00000000 00000000| Certain OTP words, such as security keys, cannot be read so they show as 00000000. |
To dump only a certain OTP word, do not use the -s parameter of the hexdump command.
Instead, use the dd command and pipe the result to hexdump.
To calculate the offset of the word, use the formula:
\$"Offset" = "Word" / 4\$
For example, for Word 48, the offset is 48 / 4 = 12.
Use dd with a block size (bs) of 4 bytes, a count of 1 word, and skip the calculated offset:
# dd status=none if=/sys/bus/nvmem/devices/stm32-romem0/nvmem of=/dev/stdout bs=4 count=1 skip=12 | hexdump -v -e '4/4 "%08x " "\n"'
7cf5f917
