Re: [PATCH v4 2/3] nvmem: add mt6323 PMIC EFUSE driver

From: Roman Vivchar <rva333@protonmail.com>

Add support for the EFUSE controller found in the Mediatek MT6323 PMIC.
The MT6323 EFUSE stores 24 bytes of hardware-related data, such as
thermal sensor calibration values.

Tested-by: Ben Grisdale <redacted> # Amazon Echo Dot (2nd Generation)
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Roman Vivchar <rva333@protonmail.com>
---
 MAINTAINERS                  |  5 +++
 drivers/nvmem/Kconfig        | 11 ++++++
 drivers/nvmem/Makefile       |  2 ++
 drivers/nvmem/mt6323-efuse.c | 84 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 102 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 3a19da74d00c..6ec0ed61260c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -16718,6 +16718,11 @@ S:	Maintained
 F:	drivers/iio/adc/mt6323-auxadc.c
 F:	include/dt-bindings/iio/adc/mediatek,mt6323-auxadc.h
 
+MEDIATEK MT6323 PMIC NVMEM DRIVER
+M:	Roman Vivchar <rva333@protonmail.com>
+S:	Maintained
+F:	drivers/nvmem/mt6323-efuse.c

+
 MEDIATEK MT6735 CLOCK & RESET DRIVERS
 M:	Yassine Oudjana [off-list ref]
 L:	linux-clk@vger.kernel.org

diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index c36c2a4c2a0b..5115c46beb97 100644
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig

@@ -328,6 +328,17 @@ config NVMEM_MTK_EFUSE
 	  This driver can also be built as a module. If so, the module
 	  will be called efuse-mtk.
 
+config NVMEM_MT6323_EFUSE
+	tristate "MediaTek MT6323 PMIC EFUSE support"
+	depends on ARCH_MEDIATEK || COMPILE_TEST
+	depends on MFD_MT6397
+	help
+	  This is a driver to access hardware related data like sensor
+	  calibration, etc.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called efuse-mt6323.
+
 config NVMEM_MXS_OCOTP
 	tristate "Freescale MXS On-Chip OTP Memory Support"
 	depends on ARCH_MXS || COMPILE_TEST

diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
index 2bbfb9ff1885..626936e4dfdd 100644
--- a/drivers/nvmem/Makefile
+++ b/drivers/nvmem/Makefile

@@ -55,6 +55,8 @@ obj-$(CONFIG_NVMEM_MICROCHIP_OTPC)	+= nvmem-microchip-otpc.o
 nvmem-microchip-otpc-y			:= microchip-otpc.o
 obj-$(CONFIG_NVMEM_MTK_EFUSE)		+= nvmem_mtk-efuse.o
 nvmem_mtk-efuse-y			:= mtk-efuse.o
+obj-$(CONFIG_NVMEM_MT6323_EFUSE)		+= nvmem_mt6323-efuse.o
+nvmem_mt6323-efuse-y			:= mt6323-efuse.o
 obj-$(CONFIG_NVMEM_MXS_OCOTP)		+= nvmem-mxs-ocotp.o
 nvmem-mxs-ocotp-y			:= mxs-ocotp.o
 obj-$(CONFIG_NVMEM_NINTENDO_OTP)	+= nvmem-nintendo-otp.o

diff --git a/drivers/nvmem/mt6323-efuse.c b/drivers/nvmem/mt6323-efuse.c
new file mode 100644
index 000000000000..6f6f1cdc2f38
--- /dev/null
+++ b/drivers/nvmem/mt6323-efuse.c

@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2026 Roman Vivchar <rva333@protonmail.com>
+ */
+
+#include <linux/err.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/types.h>
+
+#include <linux/mfd/mt6323/registers.h>
+
+#define MT6323_EFUSE_DOUT_BASE	MT6323_EFUSE_DOUT_0_15
+#define MT6323_EFUSE_SIZE	24
+
+static int mt6323_efuse_read(void *context, unsigned int offset, void *val,
+			     size_t bytes)
+{
+	struct regmap *map = context;
+	u16 *buf = val;
+	u32 tmp;
+	int ret;
+
+	/*
+	 * A manual loop using regmap_read is required because PWRAP is not
+	 * a continuous MMIO space, but rather a FSM that doesn't implement the
+	 * necessary read callback for the regmap_read_raw and regmap_read_bulk
+	 * functions.
+	 */
+	for (size_t i = 0; i < bytes; i += sizeof(*buf)) {
+		ret = regmap_read(map, MT6323_EFUSE_DOUT_BASE + offset + i, &tmp);
+		if (ret)
+			return ret;
+
+		*buf++ = tmp;
+	}
+
+	return 0;
+}
+
+static int mt6323_efuse_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct nvmem_config config = {
+		.name = "mt6323-efuse",
+		.stride = 2,
+		.word_size = 2,
+		.size = MT6323_EFUSE_SIZE,
+		.reg_read = mt6323_efuse_read,
+	};
+	struct nvmem_device *nvmem;
+	struct regmap *regmap;
+
+	/* efuse -> mfd -> pwrap */
+	regmap = dev_get_regmap(dev->parent->parent, NULL);
+	if (!regmap)
+		return dev_err_probe(dev, -ENODEV, "failed to get regmap\n");