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

Stefan Wahren
2026-04-08T16:53:09Z

Hi Gregor,

[drop Emma's old address]

Am 08.04.26 um 10:00 schrieb Gregor Herburger:
> 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.
I don't think these comments are necessary, because this applies to
other firmware drivers, too.
> + 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;
> +}
Is there any reason, why we cannot register this driver in
rpi_firmware_probe() like hwmon and clk driver?

I like to avoid the complete dt-binding from patch 1.
> +
> +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");
Raspberry Pi OTP driver ?

Regards
> +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,
>