nvmem_reg_read
rc = nvmem_reg_read(nvmem, cell->offset, buf, cell->raw_len);
rc = nvmem_reg_read(nvmem, cell->offset, &v, 1);
rc = nvmem_reg_read(nvmem,
rc = nvmem_reg_read(nvmem, offset, buf, bytes);
rc = nvmem_reg_read(nvmem, pos, buf, count);