nvmem: airoha: Add support for SMC eFUSE

Add support for SMC eFUSE on AN7581 SoC. The SoC have 2 set of 2048 bits of
eFUSE that are used to read calibration value for PCIe, Thermal, USB and
other specific info of the SoC like revision and HW device present.

eFuse value are taken by sending SMC command. ATF is responsible of
validaing the data and rejecting reading protected data (like Private
Key). In such case the SMC command will return non-zero value on a0
register.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Signed-off-by: Srinivas Kandagatla <srini@kernel.org>
Link: https://patch.msgid.link/20260530205333.117458-12-srini@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/Kconfig

@@ -28,6 +28,19 @@ source "drivers/nvmem/layouts/Kconfig"
 
 # Devices
 
+config NVMEM_AIROHA_SMC_EFUSES
+	tristate "Airoha SMC eFuse support"
+	depends on ARCH_AIROHA || COMPILE_TEST
+	depends on HAVE_ARM_SMCCC
+	default ARCH_AIROHA
+	help
+	  Say y here to enable support for reading eFuses on Airoha AN7581
+	  SoCs. These are e.g. used to store factory programmed
+	  calibration data required for the PCIe or the USB-C PHY or Thermal.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called nvmem-airoha-smc-efuses.
+
 config NVMEM_AN8855_EFUSE
 	tristate "Airoha AN8855 eFuse support"
 	depends on COMPILE_TEST

drivers/nvmem/Makefile

@@ -10,6 +10,8 @@ nvmem_layouts-y			:= layouts.o
 obj-y				+= layouts/
 
 # Devices
+obj-$(CONFIG_NVMEM_AIROHA_SMC_EFUSES)	+= nvmem-airoha-smc-efuses.o
+nvmem-airoha-smc-efuses-y 		:= airoha-smc-efuses.o
 obj-$(CONFIG_NVMEM_AN8855_EFUSE)	+= nvmem-an8855-efuse.o
 nvmem-an8855-efuse-y 			:= an8855-efuse.o
 obj-$(CONFIG_NVMEM_APPLE_EFUSES)	+= nvmem-apple-efuses.o

drivers/nvmem/airoha-smc-efuses.c

@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  Author: Christian Marangi <ansuelsmth@gmail.com>
+ */
+
+#include <linux/arm-smccc.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/platform_device.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+
+#define AIROHA_SMC_EFUSE_FID		0x82000001
+#define AIROHA_SMC_EFUSE_SUB_ID_READ	0x44414552
+
+#define AIROHA_EFUSE_CELLS		64
+
+struct airoha_efuse_bank_priv {
+	u32 bank_index;
+};
+
+static int airoha_efuse_read(void *context, unsigned int offset,
+			     void *val, size_t bytes)
+{
+	struct regmap *regmap = context;
+
+	return regmap_bulk_read(regmap, offset,
+				val, bytes / sizeof(u32));
+}
+
+static int airoha_efuse_reg_read(void *context, unsigned int offset,
+				 unsigned int *val)
+{
+	struct airoha_efuse_bank_priv *priv = context;
+	struct arm_smccc_res res;
+
+	arm_smccc_1_1_invoke(AIROHA_SMC_EFUSE_FID,
+			     AIROHA_SMC_EFUSE_SUB_ID_READ,
+			     priv->bank_index, offset, 0, 0, 0, 0, &res);
+
+	/* check if SMC reported an error */
+	if (res.a0)
+		return -EIO;
+
+	*val = res.a1;
+	return 0;
+}
+
+static int airoha_efuse_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	int ret;
+
+	for_each_child_of_node_scoped(dev->of_node, child) {
+		struct nvmem_config nvmem_config = {
+			.size = AIROHA_EFUSE_CELLS * sizeof(u32),
+			.stride = sizeof(u32),
+			.word_size = sizeof(u32),
+			.reg_read = airoha_efuse_read,
+		};
+		struct regmap_config regmap_config = {
+			.reg_read = airoha_efuse_reg_read,
+			.reg_bits = 32,
+			.val_bits = 32,
+			.reg_stride = 4,
+		};
+		struct airoha_efuse_bank_priv *priv;
+		struct nvmem_device *nvmem;
+		struct regmap *regmap;
+		const char *name;
+		u32 bank;
+
+		ret = of_property_read_u32(child, "reg", &bank);
+		if (ret)
+			return ret;
+
+		priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+		if (!priv)
+			return -ENOMEM;
+
+		name = devm_kasprintf(dev, GFP_KERNEL, "airoha-efuse-%u",
+				      bank);
+		if (!name)
+			return -ENOMEM;
+
+		priv->bank_index = bank;
+
+		regmap_config.name = name;
+		regmap = devm_regmap_init(dev, NULL, priv,
+					  &regmap_config);
+		if (IS_ERR(regmap))
+			return PTR_ERR(regmap);
+
+		nvmem_config.name = name;
+		nvmem_config.priv = regmap;
+		nvmem_config.dev = dev;
+		nvmem_config.id = bank;
+		nvmem_config.of_node = child;
+		nvmem = devm_nvmem_register(dev, &nvmem_config);
+		if (IS_ERR(nvmem))
+			return PTR_ERR(nvmem);
+	}
+
+	return 0;
+}
+
+static const struct of_device_id airoha_efuse_of_match[] = {
+	{ .compatible = "airoha,an7581-efuses", },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, airoha_efuse_of_match);
+
+static struct platform_driver airoha_efuse_driver = {
+	.probe = airoha_efuse_probe,
+	.driver = {
+		.name = "airoha-efuse",
+		.of_match_table = airoha_efuse_of_match,
+	},
+};
+module_platform_driver(airoha_efuse_driver);
+
+MODULE_AUTHOR("Christian Marangi <ansuelsmth@gmail.com>");
+MODULE_DESCRIPTION("Driver for Airoha SMC eFUSEs");
+MODULE_LICENSE("GPL");