[PATCH v4 2/5] nvmem: Add the Raspberry Pi OTP driver

[Thomas Weißschuh]

On Fri, May 08, 2026 at 04:42:45PM +0200, Gregor Herburger wrote:
> 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 at linutronix.de>
> ---
>  drivers/nvmem/Kconfig                      |  10 +++
>  drivers/nvmem/Makefile                     |   1 +
>  drivers/nvmem/raspberrypi-otp.c            | 130 +++++++++++++++++++++++++++++
>  include/soc/bcm2835/raspberrypi-firmware.h |   9 ++
>  4 files changed, 150 insertions(+)
> 
> diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
> index 74ddbd0f79b0..aac31f43385e 100644
> --- a/drivers/nvmem/Kconfig
> +++ b/drivers/nvmem/Kconfig
> @@ -483,4 +483,14 @@ 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"
> +	depends on RASPBERRYPI_FIRMWARE || (COMPILE_TEST && !RASPBERRYPI_FIRMWARE)

The '&& !RASPBERRYPI_FIRMWARE' clause looks weird, is it really necessary?

> +	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 (BCM2712 only).
> +
> +	  This driver can also be built as a module. If so, the module
> +	  will be called raspberrypi-otp.

While we are here: The empty line here is now missing.

>  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..393640cb9e32
> --- /dev/null
> +++ b/drivers/nvmem/raspberrypi-otp.c
> @@ -0,0 +1,130 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <linux/overflow.h>

This looks unused.

Instead maybe add linux/types.h, linux/align.h

> +#include <linux/module.h>
> +#include <linux/nvmem-provider.h>
> +#include <linux/platform_device.h>
> +#include <soc/bcm2835/raspberrypi-firmware.h>
> +
> +struct rpi_otp_priv {
> +	struct rpi_firmware *fw;
> +	struct device *dev;

This looks unused.

> +	u32 read_tag;
> +	u32 write_tag;
> +};
> +
> +struct rpi_otp_header {
> +	__le32 start;
> +	__le32 count;
> +	__le32 data[] __counted_by_le(count);
> +};
> +
> +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;
> +	u32 count;
> +	int ret;
> +
> +	if (!IS_ALIGNED(offset, 4) || !IS_ALIGNED(bytes, 4))
> +		return -EINVAL;

Isn't this already enforced by the nvmem core?

(...)

> +static int rpi_otp_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct nvmem_device *nvmem;
> +	struct rpi_otp_priv *priv;
> +	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,
> +		.id = NVMEM_DEVID_NONE,
> +	};
> +
> +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	data = dev_get_platdata(dev);
> +	if (!data)
> +		return -ENODEV;

I would do this before the devm_kzalloc().
> +
> +	priv->fw = dev_get_drvdata(dev->parent);
> +	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;
> +	config.size = data->size;
> +
> +	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 struct platform_driver raspberry_otp_driver = {
> +	.probe	= rpi_otp_probe,
> +	.driver = {
> +		.name	= "raspberrypi-otp",
> +	},
> +};
> +module_platform_driver(raspberry_otp_driver);
> +
> +MODULE_AUTHOR("Gregor Herburger <gregor.herburger at linutronix.de>");
> +MODULE_DESCRIPTION("Raspberry Pi OTP driver");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:raspberrypi-otp");

Instead of the manual module alias here and the implicit matching of the
platform driver this should use an explicit matching table:

static const struct platform_device_id foo_id[] = {
	{ "raspberrypi-otp" },
	{}
};
MODULE_DEVICE_TABLE(platform, foo_id);

static struct platform_driver raspberry_otp_driver = {
	...
	.id_table = foo_id,
};
module_platform_driver(raspberry_otp_driver);

(...)