[PATCH RFC 2/3] nvmem: add driver for Raspberry Pi OTP

[Stefan Wahren]

This patch brings read-only support for the Raspberry Pi Customer OTP.
The driver accesses the OTP via the mailbox property interface
provided by the VPU firmware.

Signed-off-by: Stefan Wahren <stefan.wahren at i2se.com>
---
 drivers/nvmem/Kconfig           |  10 +++
 drivers/nvmem/Makefile          |   2 +
 drivers/nvmem/raspberrypi-otp.c | 138 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 150 insertions(+)
 create mode 100644 drivers/nvmem/raspberrypi-otp.c

diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index ff505af..76b8af3 100644
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig
@@ -175,4 +175,14 @@ config NVMEM_SNVS_LPGPR
 	  This driver can also be built as a module. If so, the module
 	  will be called nvmem-snvs-lpgpr.
 
+config NVMEM_RASPBERRYPI_OTP
+	tristate "Raspberry Pi Customer OTP support"
+	depends on (ARCH_BCM2835 && RASPBERRYPI_FIRMWARE) || (COMPILE_TEST && !RASPBERRYPI_FIRMWARE)
+	depends on RASPBERRYPI_FIRMWARE
+	help
+	  This is a driver for access to the Customer OTP on the Raspberry Pi.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called nvmem-raspberrypi-otp.
+
 endif
diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
index e54dcfa..3b53b0b 100644
--- a/drivers/nvmem/Makefile
+++ b/drivers/nvmem/Makefile
@@ -37,3 +37,5 @@ obj-$(CONFIG_MESON_MX_EFUSE)	+= nvmem_meson_mx_efuse.o
 nvmem_meson_mx_efuse-y		:= meson-mx-efuse.o
 obj-$(CONFIG_NVMEM_SNVS_LPGPR)	+= nvmem_snvs_lpgpr.o
 nvmem_snvs_lpgpr-y		:= snvs_lpgpr.o
+obj-$(CONFIG_NVMEM_RASPBERRYPI_OTP)	+= nvmem-raspberrypi-otp.o
+nvmem-raspberrypi-otp-y		:= raspberrypi-otp.o
diff --git a/drivers/nvmem/raspberrypi-otp.c b/drivers/nvmem/raspberrypi-otp.c
new file mode 100644
index 0000000..e925435
--- /dev/null
+++ b/drivers/nvmem/raspberrypi-otp.c
@@ -0,0 +1,138 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Raspberry Pi Customer OTP driver
+ *
+ * Copyright (C) 2018 Stefan Wahren <stefan.wahren at i2se.com>
+ */
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <soc/bcm2835/raspberrypi-firmware.h>
+
+#define CUSTOMER_CELLS 8
+
+struct rpi_otp {
+	struct nvmem_device *nvmem;
+	struct rpi_firmware *fw;
+};
+
+/*
+ * Packet definition used by RPI_FIRMWARE_GET_CUSTOMER_OTP
+ */
+struct rpi_customer_otp_packet {
+	u32 index;
+	u32 length;
+	u32 cells[CUSTOMER_CELLS];
+};
+
+static int rpi_otp_read(void *context, unsigned int offset, void *val,
+			size_t bytes)
+{
+	struct rpi_customer_otp_packet packet;
+	struct rpi_otp *otp = context;
+	u32 *buf = val;
+	int ret;
+
+	packet.index = 0;
+	packet.length = CUSTOMER_CELLS;
+	memset(packet.cells, 0xff, sizeof(packet.cells));
+
+	ret = rpi_firmware_property(otp->fw, RPI_FIRMWARE_GET_CUSTOMER_OTP,
+				    &packet, sizeof(packet));
+
+	if (ret)
+		return ret;
+
+	/* Request rejected by firmware */
+	if (packet.index)
+		return -EIO;
+
+	while (bytes) {
+		if ((offset / 4) < sizeof(packet.cells))
+			*buf = packet.cells[offset / 4];
+		else
+			*buf = 0;
+
+		buf++;
+		bytes -= 4;
+		offset += 4;
+	}
+
+	return 0;
+}
+
+static struct nvmem_config ocotp_config = {
+	.name = "rpi-customer-otp",
+	.size = CUSTOMER_CELLS * 4,
+	.stride = 4,
+	.word_size = 4,
+	.reg_read = rpi_otp_read,
+};
+
+static int rpi_otp_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	const struct of_device_id *match;
+	struct device_node *fw_node;
+	struct rpi_otp *otp;
+
+	match = of_match_device(dev->driver->of_match_table, dev);
+	if (!match)
+		return -EINVAL;
+
+	otp = devm_kzalloc(dev, sizeof(*otp), GFP_KERNEL);
+	if (!otp)
+		return -ENOMEM;
+
+	fw_node = of_get_parent(dev->of_node);
+	if (!fw_node) {
+		dev_err(dev, "Missing firmware node\n");
+		return -ENOENT;
+	}
+
+	otp->fw = rpi_firmware_get(fw_node);
+	of_node_put(fw_node);
+	if (!otp->fw)
+		return -EPROBE_DEFER;
+
+	ocotp_config.priv = otp;
+	ocotp_config.dev = dev;
+	otp->nvmem = nvmem_register(&ocotp_config);
+	if (IS_ERR(otp->nvmem))
+		return PTR_ERR(otp->nvmem);
+
+	platform_set_drvdata(pdev, otp);
+
+	return 0;
+}
+
+static int rpi_otp_remove(struct platform_device *pdev)
+{
+	struct rpi_otp *otp = platform_get_drvdata(pdev);
+
+	return nvmem_unregister(otp->nvmem);
+}
+
+static const struct of_device_id rpi_otp_of_match[] = {
+	{ .compatible = "raspberrypi,bcm2835-customer-otp", },
+	{ /* sentinel */},
+};
+MODULE_DEVICE_TABLE(of, rpi_otp_of_match);
+
+static struct platform_driver rpi_otp_driver = {
+	.probe = rpi_otp_probe,
+	.remove = rpi_otp_remove,
+	.driver = {
+		.name = "rpi-customer-otp",
+		.of_match_table = rpi_otp_of_match,
+	},
+};
+module_platform_driver(rpi_otp_driver);
+
+MODULE_AUTHOR("Stefan Wahren <stefan.wahren at i2se.com>");
+MODULE_DESCRIPTION("Raspberry Pi Customer OTP driver");
+MODULE_LICENSE("GPL v2");
-- 
2.7.4