[PATCH 2/3] nvmem: Add the Raspberry Pi OTP driver

Gregor Herburger
2026-04-08T08:00:30Z

Raspberry Pis have OTP registers which can be accessed through the
videocore firmware. Add a nvmem driver to support these OTP registers.

Signed-off-by: Gregor Herburger <gregor.herburger@linutronix.de>
---
drivers/nvmem/Kconfig | 12 +++
drivers/nvmem/Makefile | 1 +
drivers/nvmem/raspberrypi-otp.c | 159 +++++++++++++++++++++++++++++
include/soc/bcm2835/raspberrypi-firmware.h | 2 +
4 files changed, 174 insertions(+)

diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index 74ddbd0f79b0..892d05fe67be 100644
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig
@@ -483,4 +483,16 @@ config NVMEM_QORIQ_EFUSE
This driver can also be built as a module. If so, the module
will be called nvmem_qoriq_efuse.

+config NVMEM_RASPBERRYPI_OTP
+ tristate "Raspberry Pi OTP support"
+ # Make sure not 'y' when RASPBERRYPI_FIRMWARE is 'm'. This can only
+ # happen when COMPILE_TEST=y, hence the added !RASPBERRYPI_FIRMWARE.
+ depends on RASPBERRYPI_FIRMWARE || (COMPILE_TEST && !RASPBERRYPI_FIRMWARE)
+ help
+ This driver provides access to the Raspberry Pi OTP memory via the
+ nvmem subsystem. The driver supports the customer otp as well as the
+ device specific private key OTP.
+
+ This driver can also be built as a module. If so, the module
+ will be called raspberrypi-otp.
endif
diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
index 7252b8ec88d4..8ca2095e068f 100644
--- a/drivers/nvmem/Makefile
+++ b/drivers/nvmem/Makefile
@@ -95,3 +95,4 @@ obj-$(CONFIG_NVMEM_ZYNQMP) += nvmem_zynqmp_nvmem.o
nvmem_zynqmp_nvmem-y := zynqmp_nvmem.o
obj-$(CONFIG_NVMEM_QORIQ_EFUSE) += nvmem-qoriq-efuse.o
nvmem-qoriq-efuse-y := qoriq-efuse.o
+obj-$(CONFIG_NVMEM_RASPBERRYPI_OTP) += raspberrypi-otp.o
diff --git a/drivers/nvmem/raspberrypi-otp.c b/drivers/nvmem/raspberrypi-otp.c
new file mode 100644
index 000000000000..13ee3784b137
--- /dev/null
+++ b/drivers/nvmem/raspberrypi-otp.c
@@ -0,0 +1,159 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <soc/bcm2835/raspberrypi-firmware.h>
+
+struct rpi_otp_priv {
+ struct rpi_firmware *fw;
+ struct device *dev;
+ u32 read_tag;
+ u32 write_tag;
+};
+
+struct rpi_otp_driver_data {
+ const char *name;
+ u32 read_tag;
+ u32 write_tag;
+};
+
+struct rpi_otp_header {
+ u32 start;
+ u32 count;
+ u32 data[];
+};
+
+static int rpi_otp_read(void *context, unsigned int offset, void *buf, size_t bytes)
+{
+ struct rpi_otp_priv *priv = context;
+ struct rpi_otp_header *fwbuf;
+ int ret;
+
+ fwbuf = kmalloc(sizeof(struct rpi_otp_header) + bytes, GFP_KERNEL);
+ if (!fwbuf)
+ return -ENOMEM;
+
+ fwbuf->start = offset / 4;
+ fwbuf->count = bytes / 4;
+
+ ret = rpi_firmware_property(priv->fw, priv->read_tag, fwbuf,
+ sizeof(struct rpi_otp_header) + bytes);
+ if (ret)
+ goto out;
+
+ memcpy(buf, fwbuf->data, bytes);
+
+out:
+ kfree(fwbuf);
+ return ret;
+}
+
+static int rpi_otp_write(void *context, unsigned int offset, void *val, size_t bytes)
+{
+ struct rpi_otp_priv *priv = context;
+ struct rpi_otp_header *fwbuf;
+ int ret;
+
+ fwbuf = kmalloc(sizeof(struct rpi_otp_header) + bytes, GFP_KERNEL);
+ if (!fwbuf)
+ return -ENOMEM;
+
+ fwbuf->start = offset / 4;
+ fwbuf->count = bytes / 4;
+ memcpy(fwbuf->data, val, bytes);
+
+ ret = rpi_firmware_property(priv->fw, priv->write_tag, fwbuf,
+ sizeof(struct rpi_otp_header) + bytes);
+
+ kfree(fwbuf);
+ return ret;
+}
+
+static const struct rpi_otp_driver_data rpi_otp_customer = {
+ .name = "rpi-otp-customer",
+ .read_tag = RPI_FIRMWARE_GET_CUSTOMER_OTP,
+ .write_tag = RPI_FIRMWARE_SET_CUSTOMER_OTP,
+};
+
+static const struct rpi_otp_driver_data rpi_otp_private = {
+ .name = "rpi-otp-private",
+ .read_tag = RPI_FIRMWARE_GET_PRIVATE_OTP,
+ .write_tag = RPI_FIRMWARE_SET_PRIVATE_OTP,
+};
+
+static int rpi_otp_probe(struct platform_device *pdev)
+{
+ struct device *dev = &pdev->dev;
+ struct nvmem_device *nvmem;
+ struct rpi_otp_priv *priv;
+ struct device_node *np;
+ const struct rpi_otp_driver_data *data;
+ struct nvmem_config config = {
+ .read_only = false,
+ .word_size = 4,
+ .stride = 4,
+ .reg_read = rpi_otp_read,
+ .reg_write = rpi_otp_write,
+ .size = 32,
+ };
+
+ priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+ if (!priv)
+ return -ENOMEM;
+
+ data = device_get_match_data(dev);
+ if (!data)
+ return -ENODEV;
+
+ np = of_get_parent(dev->of_node);
+ if (!np) {
+ dev_err(dev, "Missing firmware node\n");
+ return -ENOENT;
+ }
+
+ priv->fw = devm_rpi_firmware_get(&pdev->dev, np);
+ of_node_put(np);
+ if (!priv->fw)
+ return -EPROBE_DEFER;
+
+ priv->dev = dev;
+ priv->read_tag = data->read_tag;
+ priv->write_tag = data->write_tag;
+ config.dev = dev;
+ config.priv = priv;
+ config.name = data->name;
+
+ nvmem = devm_nvmem_register(dev, &config);
+ if (IS_ERR(nvmem))
+ return dev_err_probe(dev, PTR_ERR(nvmem), "error registering nvmem config\n");
+
+ return 0;
+}
+
+static const struct of_device_id rpi_otp_of_match[] = {
+ {
+ .compatible = "raspberrypi,firmware-otp-customer",
+ .data = &rpi_otp_customer
+ },
+ {
+ .compatible = "raspberrypi,firmware-otp-private",
+ .data = &rpi_otp_private,
+ },
+ { /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, rpi_otp_of_match);
+
+static struct platform_driver raspberry_otp_driver = {
+ .probe = rpi_otp_probe,
+ .driver = {
+ .name = "rpi-otp",
+ .of_match_table = rpi_otp_of_match,
+ },
+};
+module_platform_driver(raspberry_otp_driver);
+
+MODULE_AUTHOR("Gregor Herburger <gregor.herburger@linutronix.de>");
+MODULE_DESCRIPTION("Raspberry OTP driver");
+MODULE_LICENSE("GPL");
diff --git a/include/soc/bcm2835/raspberrypi-firmware.h b/include/soc/bcm2835/raspberrypi-firmware.h
index e1f87fbfe554..6e94ccf34f47 100644
--- a/include/soc/bcm2835/raspberrypi-firmware.h
+++ b/include/soc/bcm2835/raspberrypi-firmware.h
@@ -92,6 +92,8 @@ enum rpi_firmware_property_tag {
RPI_FIRMWARE_SET_POE_HAT_VAL = 0x00030050,
RPI_FIRMWARE_NOTIFY_XHCI_RESET = 0x00030058,
RPI_FIRMWARE_NOTIFY_DISPLAY_DONE = 0x00030066,
+ RPI_FIRMWARE_GET_PRIVATE_OTP = 0x00030081,
+ RPI_FIRMWARE_SET_PRIVATE_OTP = 0x00038081,

/* Dispmanx TAGS */
RPI_FIRMWARE_FRAMEBUFFER_ALLOCATE = 0x00040001,

--
2.47.3