How to read OTP with NVMEM kernel space API ( NVMEM providers and NVMEM consumers).

I'm now trying to read OTP 13~15 from remoteproc driver to enc/decrypt m4 firmware.

From NVMEM overview. I learn below information

1. OTP 13~15 are non-secured area​
2. The name of device is "stm32-romem0"
3. NVMEM kernel API

I can successfully get OTP 13~15 from user space.

To get OTP 13~15 in linux kernel I write code that read nvmem device with the NVMEM kernel API.

I define a match function​​

int rproc_nvmem_match(struct device *dev, const void *data){

const char *device_name = dev_name(dev);

const char *p_name = data;

int length = strlen(p_name);

​

if (memcmp(p_name, device_name, length) != 0) return 0;

return 1;

}

​

​Then, use nvmem_device_find and nvmem_device_read to read OTP 13~15. ( I use offset both 0x5C005234 and 0x234. )

​

u8 *buf_uniqueId;

buf_uniqueId = kmalloc(24, GFP_KERNEL);

struct nvmem_device *nvmem = nvmem_device_find("stm32-romem0", rproc_nvmem_match);

int err = nvmem_device_read(nvmem, 0x234, 24, (void*)buf_uniqueId);

if (!nvmem)

printk("nvmem error");

printk("err : %d", err);

​

But I can't get OTP 13~15. I get "err : -22" from minicom.

I don't know which part is wrong. Is there any configuration to use nvmem driver or my code is wrong?

Can you give me a example code to read OTP from linux kernel?

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