[PATCH v5 0/3] Add support for STMicroelectronics M24LR EEPROM/NFC chips

[PATCH v5 0/3] Add support for STMicroelectronics M24LR EEPROM/NFC chips

[Abd-Alrhman Masalkhi]

This patch series adds support for the STMicroelectronics M24LR series
RFID/NFC EEPROM devices. These chips expose two I2C addresses: the primary
one provides access to system control and configuration registers, while
the secondary address is used for EEPROM access.

The driver implements both functionalities:
 - A sysfs-based interface for the control and system parameter registers.
 - EEPROM access via the nvmem subsystem using a secondary I2C dummy
   client.

Tested on: M24LR04E-R using Yocto on Raspberry Pi 4

Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>

Abd-Alrhman Masalkhi (3):
  dt-bindings: eeprom: Add ST M24LR support
  eeprom: add driver for ST M24LR series RFID/NFC EEPROM chips
  ABI: sysfs: add documentation for ST M24LR EEPROM and control
    interface

 .../ABI/testing/sysfs-bus-i2c-devices-m24lr   | 100 +++
 .../devicetree/bindings/eeprom/st,m24lr.yaml  |  52 ++
 drivers/misc/eeprom/Kconfig                   |  18 +
 drivers/misc/eeprom/Makefile                  |   1 +
 drivers/misc/eeprom/m24lr.c                   | 653 ++++++++++++++++++
 5 files changed, 824 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-i2c-devices-m24lr
 create mode 100644 Documentation/devicetree/bindings/eeprom/st,m24lr.yaml
 create mode 100644 drivers/misc/eeprom/m24lr.c

-- 
2.43.0

[PATCH v5 1/3] dt-bindings: eeprom: Add ST M24LR support

[Abd-Alrhman Masalkhi]

Add support for STMicroelectronics M24LR RFID/NFC EEPROM chips.
These devices use two I2C addresses: the primary address provides
access to control and system parameter registers, while the
secondary address is used for EEPROM access.

Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
---
Changes in v5:
 - No changes and already reviewed by Krzysztof Kozlowski
 - Link to v4: https://lore.kernel.org/lkml/20250608182714.3359441-2-abd.masalkhi@gmail.com/

Changes in v4:
 - Moved the binding file to the eeprom/ directory
 - Updated reg property to use items: with per-address descriptions
   instead of minItems/maxItems
 - Link to v3: https://lore.kernel.org/lkml/20250606120631.3140054-2-abd.masalkhi@gmail.com/

Changes in v3:
 - Dropped reference to the i2c-mux binding.
 - Added reference to the nvmem binding to reflect EEPROM usage.
 - Updated 'reg' property to represent the device using two I2C addresses.
 - Fixed DT schema errors and yamllint warnings.
 - Removed the unused 'pagesize' property.
 - Link to v2: https://lore.kernel.org/lkml/20250601153022.2027919-2-abd.masalkhi@gmail.com/

Changes in v2:
 - Moved file from misc/ to eeprom/.
 - Updated $id and $ref paths.
 - Reformatted maintainers field.
 - Clarified description text.
 - Added enum and default to pagesize.
 - Replaced additionalProperties with unevaluatedProperties.
 - Revised example to use explicit i2c mux layout.
 - Fixed style and formatting issues.
 - Link to v1: https://lore.kernel.org/lkml/20250531081159.2007319-2-abd.masalkhi@gmail.com/
---
 .../devicetree/bindings/eeprom/st,m24lr.yaml  | 52 +++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/eeprom/st,m24lr.yaml

diff --git a/Documentation/devicetree/bindings/eeprom/st,m24lr.yaml b/Documentation/devicetree/bindings/eeprom/st,m24lr.yaml
new file mode 100644
index 000000000000..0a0820e9d11f
--- /dev/null
+++ b/Documentation/devicetree/bindings/eeprom/st,m24lr.yaml
@@ -0,0 +1,52 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/eeprom/st,m24lr.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: STMicroelectronics M24LR NFC/RFID EEPROM
+
+maintainers:
+  - Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
+
+description:
+  STMicroelectronics M24LR series are dual-interface (RF + I2C)
+  EEPROM chips. These devices support I2C-based access to both
+  memory and a system area that controls authentication and configuration.
+  They expose two I2C addresses, one for the system parameter sector and
+  one for the EEPROM.
+
+allOf:
+  - $ref: /schemas/nvmem/nvmem.yaml#
+
+properties:
+  compatible:
+    enum:
+      - st,m24lr04e-r
+      - st,m24lr16e-r
+      - st,m24lr64e-r
+
+  reg:
+    items:
+      - description: I2C address used for control/system registers
+      - description: I2C address used for EEPROM memory access
+
+required:
+  - compatible
+  - reg
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      eeprom@57 {
+        compatible = "st,m24lr04e-r";
+        reg = <0x57>, /* primary-device */
+              <0x53>; /* secondary-device */
+      };
+    };
+...
-- 
2.43.0

[PATCH v5 2/3] eeprom: add driver for ST M24LR series RFID/NFC EEPROM chips

[Abd-Alrhman Masalkhi]

adds support for STMicroelectronics M24LRxx devices, which expose
two separate I2C addresses: one for system control and one for EEPROM
access. The driver implements both a sysfs-based interface for control
registers (e.g. UID, password authentication) and an nvmem provider
for EEPROM access.

Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
---
Changes in v5:
 - Fixed function signatures in m24lr_ctl_sss_read and m24lr_ctl_sss_write
   to use const struct bin_attribute *attr
 - Link to v4: https://lore.kernel.org/lkml/20250608182714.3359441-3-abd.masalkhi@gmail.com/

Changes in v4:
 - Moved the source file to the eeprom/ directory
 - Removed use of unlikely() macro
 - Removed use of EIO as a fallback error
 - Stopped dynamically creating sysfs attributes
 - Replaced per-sector SSS attributes with a single bin_attribute
   for all SSS
 - Introduced total_sectors sysfs attribute to report the number
   of valid sectors
 - Avoided sharing a single show/store callback across multiple
   attribute types
 - Link to v3: https://lore.kernel.org/lkml/20250606120631.3140054-3-abd.masalkhi@gmail.com/

Changes in v3:
 - Fully support the M24LR chips, including EEPROM access, no need for
   the standard at24 driver to handle EEPROM separately.
 - Rename the driver file from m24lr_ctl.c to m24lr.c.
 - Rename all identifiers from the m24lr_ctl prefix to m24lr.
 - Retain the m24lr_ctl prefix for control-related routines to distinguish
   them from EEPROM-related logic.
 - Drop usage of the I2C mux API.
 - Use the NVMEM subsystem to handle EEPROM access.
 - Add REGMAP support for EEPROM register access.
 - Update Kconfig entry to reflect that the driver now supports both
   control and EEPROM functionality.
 - Link to v2: https://lore.kernel.org/lkml/20250601153022.2027919-3-abd.masalkhi@gmail.com/

Changes in v2:
 - Fix compiling Errors and Warnings
 - Replace scnprintf with sysfs_emit
 - Drop success log message from probe.
 - Link to v1: https://lore.kernel.org/lkml/20250531081159.2007319-3-abd.masalkhi@gmail.com/

Comment:
 - Running checkpatch emit a warning for non-const regmap_config.
   The variable must remain auto and mutable due to runtime manipulation.
---
 drivers/misc/eeprom/Kconfig  |  18 +
 drivers/misc/eeprom/Makefile |   1 +
 drivers/misc/eeprom/m24lr.c  | 653 +++++++++++++++++++++++++++++++++++
 3 files changed, 672 insertions(+)
 create mode 100644 drivers/misc/eeprom/m24lr.c

diff --git a/drivers/misc/eeprom/Kconfig b/drivers/misc/eeprom/Kconfig
index cb1c4b8e7fd3..cb0ce243babd 100644
--- a/drivers/misc/eeprom/Kconfig
+++ b/drivers/misc/eeprom/Kconfig
@@ -119,4 +119,22 @@ config EEPROM_EE1004
 	  This driver can also be built as a module.  If so, the module
 	  will be called ee1004.
 
+config EEPROM_M24LR
+	tristate "STMicroelectronics M24LR RFID/NFC EEPROM support"
+	depends on I2C && SYSFS
+	select REGMAP_I2C
+	select NVMEM
+	select NVMEM_SYSFS
+	help
+	  This enables support for STMicroelectronics M24LR RFID/NFC EEPROM
+	  chips. These dual-interface devices expose two I2C addresses:
+	  one for EEPROM memory access and another for control and system
+	  configuration (e.g. UID, password handling).
+
+	  This driver provides a sysfs interface for control functions and
+	  integrates with the nvmem subsystem for EEPROM access.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called m24lr.
+
 endmenu
diff --git a/drivers/misc/eeprom/Makefile b/drivers/misc/eeprom/Makefile
index 65794e526d5d..8f311fd6a4ce 100644
--- a/drivers/misc/eeprom/Makefile
+++ b/drivers/misc/eeprom/Makefile
@@ -7,3 +7,4 @@ obj-$(CONFIG_EEPROM_93XX46)	+= eeprom_93xx46.o
 obj-$(CONFIG_EEPROM_DIGSY_MTC_CFG) += digsy_mtc_eeprom.o
 obj-$(CONFIG_EEPROM_IDT_89HPESX) += idt_89hpesx.o
 obj-$(CONFIG_EEPROM_EE1004)	+= ee1004.o
+obj-$(CONFIG_EEPROM_M24LR) += m24lr.o
diff --git a/drivers/misc/eeprom/m24lr.c b/drivers/misc/eeprom/m24lr.c
new file mode 100644
index 000000000000..497770de3a00
--- /dev/null
+++ b/drivers/misc/eeprom/m24lr.c
@@ -0,0 +1,653 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * m24lr.c - Sysfs control interface for ST M24LR series RFID/NFC chips
+ *
+ * Copyright (c) 2025 Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
+ *
+ * This driver implements both the sysfs-based control interface and EEPROM
+ * access for STMicroelectronics M24LR series chips (e.g., M24LR04E-R).
+ * It provides access to control registers for features such as password
+ * authentication, memory protection, and device configuration. In addition,
+ * it manages read and write operations to the EEPROM region of the chip.
+ */
+
+#include <linux/i2c.h>
+#include <linux/regmap.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/nvmem-provider.h>
+
+#define M24LR_WRITE_TIMEOUT	  25u
+#define M24LR_READ_TIMEOUT	  (M24LR_WRITE_TIMEOUT)
+
+/**
+ * struct m24lr_chip - describes chip-specific sysfs layout
+ * @page_size:	   chip-specific limit on the maximum number of bytes allowed
+ *		   in a single write operation.
+ * @eeprom_size:   size of the EEPROM in byte
+ * @sss_len:       the length of the sss region
+ *
+ * Supports multiple M24LR chip variants (e.g., M24LRxx) by allowing each
+ * to define its own set of sysfs attributes, depending on its available
+ * registers and features.
+ */
+struct m24lr_chip {
+	unsigned int page_size;
+	unsigned int eeprom_size;
+	unsigned int sss_len;
+};
+
+/**
+ * struct m24lr - core driver data for M24LR chip control
+ * @uid:           64 bits unique identifier stored in the device
+ * @sss_len:       the length of the sss region
+ * @page_size:	   chip-specific limit on the maximum number of bytes allowed
+ *		   in a single write operation.
+ * @eeprom_size:   size of the EEPROM in byte
+ * @ctl_regmap:	   regmap interface for accessing the system parameter sector
+ * @eeprom_regmap: regmap interface for accessing the EEPROM
+ * @lock:	   mutex to synchronize operations to the device
+ *
+ * Central data structure holding the state and resources used by the
+ * M24LR device driver.
+ */
+struct m24lr {
+	u64 uid;
+	unsigned int sss_len;
+	unsigned int page_size;
+	unsigned int eeprom_size;
+	struct regmap *ctl_regmap;
+	struct regmap *eeprom_regmap;
+	struct mutex lock;	 /* synchronize operations to the device */
+};
+
+static const struct regmap_range m24lr_ctl_vo_ranges[] = {
+	regmap_reg_range(0, 63),
+};
+
+static const struct regmap_access_table m24lr_ctl_vo_table = {
+	.yes_ranges = m24lr_ctl_vo_ranges,
+	.n_yes_ranges = ARRAY_SIZE(m24lr_ctl_vo_ranges),
+};
+
+static const struct regmap_config m24lr_ctl_regmap_conf = {
+	.name = "m24lr_ctl",
+	.reg_stride = 1,
+	.reg_bits = 16,
+	.val_bits = 8,
+	.disable_locking = false,
+	.cache_type = REGCACHE_RBTREE,/* Flat can't be used, there's huge gap */
+	.volatile_table = &m24lr_ctl_vo_table,
+};
+
+/* Chip descriptor for M24LR04E-R variant */
+static const struct m24lr_chip m24lr04e_r_chip = {
+	.page_size = 4,
+	.eeprom_size = 512,
+	.sss_len = 4,
+};
+
+/* Chip descriptor for M24LR16E-R variant */
+static const struct m24lr_chip m24lr16e_r_chip = {
+	.page_size = 4,
+	.eeprom_size = 2048,
+	.sss_len = 16,
+};
+
+/* Chip descriptor for M24LR64E-R variant */
+static const struct m24lr_chip m24lr64e_r_chip = {
+	.page_size = 4,
+	.eeprom_size = 8192,
+	.sss_len = 64,
+};
+
+static const struct i2c_device_id m24lr_ids[] = {
+	{ "m24lr04e-r", (kernel_ulong_t)&m24lr04e_r_chip},
+	{ "m24lr16e-r", (kernel_ulong_t)&m24lr16e_r_chip},
+	{ "m24lr64e-r", (kernel_ulong_t)&m24lr64e_r_chip},
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, m24lr_ids);
+
+static const struct of_device_id m24lr_of_match[] = {
+	{ .compatible = "st,m24lr04e-r", .data = &m24lr04e_r_chip},
+	{ .compatible = "st,m24lr16e-r", .data = &m24lr16e_r_chip},
+	{ .compatible = "st,m24lr64e-r", .data = &m24lr64e_r_chip},
+	{ }
+};
+MODULE_DEVICE_TABLE(of, m24lr_of_match);
+
+/**
+ * m24lr_parse_le_value - Parse hex string and convert to little-endian binary
+ * @buf:	Input string buffer (hex format)
+ * @reg_size:	Size of the register in bytes (must be 1, 2, 4, or 8)
+ * @output:	Output buffer to store the value in little-endian format
+ *
+ * Converts a hexadecimal string to a numeric value of the given register size
+ * and writes it in little-endian byte order into the provided buffer.
+ *
+ * Return: 0 on success, or negative error code on failure
+ */
+static __maybe_unused int m24lr_parse_le_value(const char *buf, u32 reg_size,
+					       u8 *output)
+{
+	int err;
+
+	switch (reg_size) {
+	case 1: {
+		u8 tmp;
+
+		err = kstrtou8(buf, 16, &tmp);
+		if (!err)
+			*output = tmp;
+		break;
+	}
+	case 2: {
+		u16 tmp;
+
+		err = kstrtou16(buf, 16, &tmp);
+		if (!err)
+			*(__le16 *)output = cpu_to_le16(tmp);
+		break;
+	}
+	case 4: {
+		u32 tmp;
+
+		err = kstrtou32(buf, 16, &tmp);
+		if (!err)
+			*(__le32 *)output = cpu_to_le32(tmp);
+		break;
+	}
+	case 8: {
+		u64 tmp;
+
+		err = kstrtou64(buf, 16, &tmp);
+		if (!err)
+			*(__le64 *)output = cpu_to_le64(tmp);
+		break;
+	}
+	default:
+		err = -EINVAL;
+	}
+
+	return err;
+}
+
+/**
+ * m24lr_regmap_read - read data using regmap with retry on failure
+ * @regmap:  regmap instance for the device
+ * @buf:     buffer to store the read data
+ * @size:    number of bytes to read
+ * @offset:  starting register address
+ *
+ * Attempts to read a block of data from the device with retries and timeout.
+ * Some M24LR chips may transiently NACK reads (e.g., during internal write
+ * cycles), so this function retries with a short sleep until the timeout
+ * expires.
+ *
+ * Returns:
+ *	 Number of bytes read on success,
+ *	 -ETIMEDOUT if the read fails within the timeout window.
+ */
+static ssize_t m24lr_regmap_read(struct regmap *regmap, u8 *buf,
+				 size_t size, unsigned int offset)
+{
+	int err;
+	unsigned long timeout, read_time;
+	ssize_t ret = -ETIMEDOUT;
+
+	timeout = jiffies + msecs_to_jiffies(M24LR_READ_TIMEOUT);
+	do {
+		read_time = jiffies;
+
+		err = regmap_bulk_read(regmap, offset, buf, size);
+		if (!err) {
+			ret = size;
+			break;
+		}
+
+		usleep_range(1000, 2000);
+	} while (time_before(read_time, timeout));
+
+	return ret;
+}
+
+/**
+ * m24lr_regmap_write - write data using regmap with retry on failure
+ * @regmap: regmap instance for the device
+ * @buf:    buffer containing the data to write
+ * @size:   number of bytes to write
+ * @offset: starting register address
+ *
+ * Attempts to write a block of data to the device with retries and a timeout.
+ * Some M24LR devices may NACK I2C writes while an internal write operation
+ * is in progress. This function retries the write operation with a short delay
+ * until it succeeds or the timeout is reached.
+ *
+ * Returns:
+ *	 Number of bytes written on success,
+ *	 -ETIMEDOUT if the write fails within the timeout window.
+ */
+static ssize_t m24lr_regmap_write(struct regmap *regmap, const u8 *buf,
+				  size_t size, unsigned int offset)
+{
+	int err;
+	unsigned long timeout, write_time;
+	ssize_t ret = -ETIMEDOUT;
+
+	timeout = jiffies + msecs_to_jiffies(M24LR_WRITE_TIMEOUT);
+
+	do {
+		write_time = jiffies;
+
+		err = regmap_bulk_write(regmap, offset, buf, size);
+		if (!err) {
+			ret = size;
+			break;
+		}
+
+		usleep_range(1000, 2000);
+	} while (time_before(write_time, timeout));
+
+	return ret;
+}
+
+static ssize_t m24lr_read(struct m24lr *m24lr, u8 *buf, size_t size,
+			  unsigned int offset, bool is_eeprom)
+{
+	struct regmap *regmap;
+	long ret;
+
+	if (is_eeprom)
+		regmap = m24lr->eeprom_regmap;
+	else
+		regmap = m24lr->ctl_regmap;
+
+	mutex_lock(&m24lr->lock);
+	ret = m24lr_regmap_read(regmap, buf, size, offset);
+	mutex_unlock(&m24lr->lock);
+
+	return ret;
+}
+
+/**
+ * m24lr_write - write buffer to M24LR device with page alignment handling
+ * @m24lr:     pointer to driver context
+ * @buf:       data buffer to write
+ * @size:      number of bytes to write
+ * @offset:    target register address in the device
+ * @is_eeprom: true if the write should target the EEPROM,
+ *             false if it should target the system parameters sector.
+ *
+ * Writes data to the M24LR device using regmap, split into chunks no larger
+ * than page_size to respect device-specific write limitations (e.g., page
+ * size or I2C hold-time concerns). Each chunk is aligned to the page boundary
+ * defined by page_size.
+ *
+ * Returns:
+ *	 Total number of bytes written on success,
+ *	 A negative error code if any write fails.
+ */
+static ssize_t m24lr_write(struct m24lr *m24lr, const u8 *buf, size_t size,
+			   unsigned int offset, bool is_eeprom)
+{
+	unsigned int n, next_sector;
+	struct regmap *regmap;
+	ssize_t ret = 0;
+	long err;
+
+	if (is_eeprom)
+		regmap = m24lr->eeprom_regmap;
+	else
+		regmap = m24lr->ctl_regmap;
+
+	n = min(size, m24lr->page_size);
+	next_sector = roundup(offset + 1, m24lr->page_size);
+	if (offset + n > next_sector)
+		n = next_sector - offset;
+
+	mutex_lock(&m24lr->lock);
+	while (n) {
+		err = m24lr_regmap_write(regmap, buf, n, offset);
+		if (IS_ERR_VALUE(err)) {
+			mutex_unlock(&m24lr->lock);
+			if (ret)
+				return ret;
+			else
+				return err;
+		}
+
+		offset += n;
+		size -= n;
+		ret += n;
+		n = min(size, m24lr->page_size);
+	}
+	mutex_unlock(&m24lr->lock);
+
+	return ret;
+}
+
+/**
+ * m24lr_write_pass - Write password to M24LR043-R using secure format
+ * @m24lr: Pointer to device control structure
+ * @buf:   Input buffer containing hex-encoded password
+ * @count: Number of bytes in @buf
+ * @code:  Operation code to embed between password copies
+ *
+ * This function parses a 4-byte password, encodes it in  big-endian format,
+ * and constructs a 9-byte sequence of the form:
+ *
+ *	  [BE(password), code, BE(password)]
+ *
+ * The result is written to register 0x0900 (2304), which is the password
+ * register in M24LR04E-R chip.
+ *
+ * Return: Number of bytes written on success, or negative error code on failure
+ */
+static ssize_t m24lr_write_pass(struct m24lr *m24lr, const char *buf,
+				size_t count, u8 code)
+{
+	__be32 be_pass;
+	u8 output[9];
+	long ret;
+	u32 pass;
+	int err;
+
+	if (!count)
+		return -EINVAL;
+
+	if (count > 8)
+		return -EINVAL;
+
+	err = kstrtou32(buf, 16, &pass);
+	if (err)
+		return err;
+
+	be_pass = cpu_to_be32(pass);
+
+	memcpy(output, &be_pass, sizeof(be_pass));
+	output[4] = code;
+	memcpy(output + 5, &be_pass, sizeof(be_pass));
+
+	mutex_lock(&m24lr->lock);
+	ret = m24lr_regmap_write(m24lr->ctl_regmap, output, 9, 2304);
+	mutex_unlock(&m24lr->lock);
+
+	return ret;
+}
+
+static ssize_t m24lr_read_reg_le(struct m24lr *m24lr, u64 *val,
+				 unsigned int reg_addr,
+				 unsigned int reg_size)
+{
+	long ret;
+	__le64 input = 0;
+
+	ret = m24lr_read(m24lr, (u8 *)&input, reg_size, reg_addr, false);
+	if (IS_ERR_VALUE(ret))
+		return ret;
+
+	if (ret != reg_size)
+		return -EINVAL;
+
+	switch (reg_size) {
+	case 1:
+		*val = *(u8 *)&input;
+		break;
+	case 2:
+		*val = le16_to_cpu((__le16)input);
+		break;
+	case 4:
+		*val = le32_to_cpu((__le32)input);
+		break;
+	case 8:
+		*val = le64_to_cpu((__le64)input);
+		break;
+	default:
+		return -EINVAL;
+	};
+
+	return 0;
+}
+
+static int m24lr_nvmem_read(void *priv, unsigned int offset, void *val,
+			    size_t bytes)
+{
+	struct m24lr *m24lr = priv;
+
+	if (!bytes)
+		return bytes;
+
+	if (offset + bytes > m24lr->eeprom_size)
+		return -EINVAL;
+
+	return m24lr_read(m24lr, val, bytes, offset, true);
+}
+
+static int m24lr_nvmem_write(void *priv, unsigned int offset, void *val,
+			     size_t bytes)
+{
+	struct m24lr *m24lr = priv;
+
+	if (!bytes)
+		return -EINVAL;
+
+	if (offset + bytes > m24lr->eeprom_size)
+		return -EINVAL;
+
+	return m24lr_write(m24lr, val, bytes, offset, true);
+}
+
+static ssize_t m24lr_ctl_sss_read(struct file *filep, struct kobject *kobj,
+				  const struct bin_attribute *attr, char *buf,
+				  loff_t offset, size_t count)
+{
+	struct m24lr *m24lr = attr->private;
+
+	if (!count)
+		return count;
+
+	if (offset + count > m24lr->sss_len)
+		return -EINVAL;
+
+	return m24lr_read(m24lr, buf, count, offset, false);
+}
+
+static ssize_t m24lr_ctl_sss_write(struct file *filep, struct kobject *kobj,
+				   const struct bin_attribute *attr, char *buf,
+				   loff_t offset, size_t count)
+{
+	struct m24lr *m24lr = attr->private;
+
+	if (!count)
+		return -EINVAL;
+
+	if (offset + count > m24lr->sss_len)
+		return -EINVAL;
+
+	return m24lr_write(m24lr, buf, count, offset, false);
+}
+static BIN_ATTR(sss, 0600, m24lr_ctl_sss_read, m24lr_ctl_sss_write, 0);
+
+static ssize_t new_pass_store(struct device *dev, struct device_attribute *attr,
+			      const char *buf, size_t count)
+{
+	struct m24lr *m24lr = i2c_get_clientdata(to_i2c_client(dev));
+
+	return m24lr_write_pass(m24lr, buf, count, 7);
+}
+static DEVICE_ATTR_WO(new_pass);
+
+static ssize_t unlock_store(struct device *dev, struct device_attribute *attr,
+			    const char *buf, size_t count)
+{
+	struct m24lr *m24lr = i2c_get_clientdata(to_i2c_client(dev));
+
+	return m24lr_write_pass(m24lr, buf, count, 9);
+}
+static DEVICE_ATTR_WO(unlock);
+
+static ssize_t uid_show(struct device *dev, struct device_attribute *attr,
+			char *buf)
+{
+	struct m24lr *m24lr = i2c_get_clientdata(to_i2c_client(dev));
+
+	return sysfs_emit(buf, "%llx\n", m24lr->uid);
+}
+static DEVICE_ATTR_RO(uid);
+
+static ssize_t total_sectors_show(struct device *dev,
+				  struct device_attribute *attr, char *buf)
+{
+	struct m24lr *m24lr = i2c_get_clientdata(to_i2c_client(dev));
+
+	return sysfs_emit(buf, "%x\n", m24lr->sss_len);
+}
+static DEVICE_ATTR_RO(total_sectors);
+
+static struct attribute *m24lr_ctl_dev_attrs[] = {
+	&dev_attr_unlock.attr,
+	&dev_attr_new_pass.attr,
+	&dev_attr_uid.attr,
+	&dev_attr_total_sectors.attr,
+	NULL,
+};
+
+static const struct m24lr_chip *m24lr_get_chip(struct device *dev)
+{
+	const struct m24lr_chip *ret;
+	const struct i2c_device_id *id;
+
+	id = i2c_match_id(m24lr_ids, to_i2c_client(dev));
+
+	if (dev->of_node && of_match_device(m24lr_of_match, dev))
+		ret = of_device_get_match_data(dev);
+	else if (id)
+		ret = (void *)id->driver_data;
+	else
+		ret = acpi_device_get_match_data(dev);
+
+	return ret;
+}
+
+static int m24lr_probe(struct i2c_client *client)
+{
+	struct regmap_config eeprom_regmap_conf = {0};
+	struct nvmem_config nvmem_conf = {0};
+	struct device *dev = &client->dev;
+	struct i2c_client *eeprom_client;
+	const struct m24lr_chip *chip;
+	struct regmap *eeprom_regmap;
+	struct nvmem_device *nvmem;
+	struct regmap *ctl_regmap;
+	struct m24lr *m24lr;
+	u32 regs[2];
+	long err;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
+		return -EOPNOTSUPP;
+
+	chip = m24lr_get_chip(dev);
+	if (!chip)
+		return -ENODEV;
+
+	m24lr = devm_kzalloc(dev, sizeof(struct m24lr), GFP_KERNEL);
+	if (!m24lr)
+		return -ENOMEM;
+
+	err = device_property_read_u32_array(dev, "reg", regs, ARRAY_SIZE(regs));
+	if (err) {
+		dev_err(dev, "device_property_read_u32_array\n");
+		return err;
+	}
+	/* Create a second I2C client for the eeprom interface */
+	eeprom_client = devm_i2c_new_dummy_device(dev, client->adapter, regs[1]);
+	if (IS_ERR(eeprom_client)) {
+		dev_err(dev,
+			"Failed to create dummy I2C client for the EEPROM\n");
+		return PTR_ERR(eeprom_client);
+	}
+
+	ctl_regmap = devm_regmap_init_i2c(client, &m24lr_ctl_regmap_conf);
+	if (IS_ERR(ctl_regmap)) {
+		err = PTR_ERR(ctl_regmap);
+		dev_err(dev, "Failed to init regmap\n");
+		return err;
+	}
+
+	eeprom_regmap_conf.name = "m24lr_eeprom";
+	eeprom_regmap_conf.reg_bits = 16;
+	eeprom_regmap_conf.val_bits = 8;
+	eeprom_regmap_conf.disable_locking = true;
+	eeprom_regmap_conf.max_register = chip->eeprom_size - 1;
+
+	eeprom_regmap = devm_regmap_init_i2c(eeprom_client,
+					     &eeprom_regmap_conf);
+	if (IS_ERR(eeprom_regmap)) {
+		err = PTR_ERR(eeprom_regmap);
+		dev_err(dev, "Failed to init regmap\n");
+		return err;
+	}
+
+	mutex_init(&m24lr->lock);
+	m24lr->sss_len = chip->sss_len;
+	m24lr->page_size = chip->page_size;
+	m24lr->eeprom_size = chip->eeprom_size;
+	m24lr->eeprom_regmap = eeprom_regmap;
+	m24lr->ctl_regmap = ctl_regmap;
+
+	nvmem_conf.dev = &eeprom_client->dev;
+	nvmem_conf.owner = THIS_MODULE;
+	nvmem_conf.type = NVMEM_TYPE_EEPROM;
+	nvmem_conf.reg_read = m24lr_nvmem_read;
+	nvmem_conf.reg_write = m24lr_nvmem_write;
+	nvmem_conf.size = chip->eeprom_size;
+	nvmem_conf.word_size = 1;
+	nvmem_conf.stride = 1;
+	nvmem_conf.priv = m24lr;
+
+	nvmem = devm_nvmem_register(dev, &nvmem_conf);
+	if (IS_ERR(nvmem))
+		return PTR_ERR(nvmem);
+
+	i2c_set_clientdata(client, m24lr);
+	i2c_set_clientdata(eeprom_client, m24lr);
+
+	bin_attr_sss.size = chip->sss_len;
+	bin_attr_sss.private = m24lr;
+	err = sysfs_create_bin_file(&dev->kobj, &bin_attr_sss);
+	if (err)
+		return err;
+
+	/* test by reading the uid, if success store it */
+	err = m24lr_read_reg_le(m24lr, &m24lr->uid, 2324, sizeof(m24lr->uid));
+	if (IS_ERR_VALUE(err))
+		return -ENODEV;
+
+	return 0;
+}
+
+static void m24lr_remove(struct i2c_client *client)
+{
+	sysfs_remove_bin_file(&client->dev.kobj, &bin_attr_sss);
+}
+
+ATTRIBUTE_GROUPS(m24lr_ctl_dev);
+
+static struct i2c_driver m24lr_driver = {
+	.driver = {
+		.name = "m24lr",
+		.of_match_table = m24lr_of_match,
+		.dev_groups = m24lr_ctl_dev_groups,
+	},
+	.probe	  = m24lr_probe,
+	.remove = m24lr_remove,
+	.id_table = m24lr_ids,
+};
+module_i2c_driver(m24lr_driver);
+
+MODULE_AUTHOR("Abd-Alrhman Masalkhi");
+MODULE_DESCRIPTION("st m24lr control driver");
+MODULE_LICENSE("GPL");
-- 
2.43.0

[PATCH v5 3/3] ABI: sysfs: add documentation for ST M24LR EEPROM and control interface

[Abd-Alrhman Masalkhi]

Add sysfs ABI documentation for the STMicroelectronics M24LR device,
covering both the control interface (e.g., unlock, password update, UID,
total sectors, and SSS entries) and EEPROM access via the nvmem subsystem.

Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
---
Changes in v5:
 - Fix dates and update targeted kernel version.
 - Link to v4: https://lore.kernel.org/lkml/20250608182714.3359441-4-abd.masalkhi@gmail.com/

Changes in v4:
 - Replaced 'sss<N>' entries with a single binary 'sss' attribute
 - Added 'total_sectors' attribute to report the number of valid SSS bytes
 - removed 'mem_size' attribute
 - Fix dates and update targeted kernel version.
 - Link to v3: https://lore.kernel.org/lkml/20250606120631.3140054-4-abd.masalkhi@gmail.com/

Changes in v3:
 - Updated sysfs entry paths to use <busnum>-<primary-addr> to reflect the
   control address.
 - Link to v2: https://lore.kernel.org/lkml/20250601153022.2027919-4-abd.masalkhi@gmail.com/

Changes in v2:
 - Added initial sysfs ABI documentation.
---
 .../ABI/testing/sysfs-bus-i2c-devices-m24lr   | 100 ++++++++++++++++++
 1 file changed, 100 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-i2c-devices-m24lr

diff --git a/Documentation/ABI/testing/sysfs-bus-i2c-devices-m24lr b/Documentation/ABI/testing/sysfs-bus-i2c-devices-m24lr
new file mode 100644
index 000000000000..7c51ce8d38ba
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-i2c-devices-m24lr
@@ -0,0 +1,100 @@
+What:           /sys/bus/i2c/devices/<busnum>-<primary-addr>/unlock
+Date:           2025-07-04
+KernelVersion:  6.17
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
+Description:
+                Write-only attribute used to present a password and unlock
+                access to protected areas of the M24LR chip, including
+                configuration registers such as the Sector Security Status
+                (SSS) bytes. A valid password must be written to enable write
+                access to these regions via the I2C interface.
+
+                Format:
+                  - Hexadecimal string representing a 32-bit (4-byte) password
+                  - Accepts 1 to 8 hex digits (e.g., "c", "1F", "a1b2c3d4")
+                  - No "0x" prefix, whitespace, or trailing newline
+                  - Case-insensitive
+
+                Behavior:
+                  - If the password matches the internal stored value,
+                    access to protected memory/configuration is granted
+                  - If the password does not match the internally stored value,
+                    it will fail silently
+
+What:           /sys/bus/i2c/devices/<busnum>-<primary-addr>/new_pass
+Date:           2025-07-04
+KernelVersion:  6.17
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
+Description:
+                Write-only attribute used to update the password required to
+                unlock the M24LR chip.
+
+                Format:
+                  - Hexadecimal string representing a new 32-bit password
+                  - Accepts 1 to 8 hex digits (e.g., "1A", "ffff", "c0ffee00")
+                  - No "0x" prefix, whitespace, or trailing newline
+                  - Case-insensitive
+
+                Behavior:
+                  - Overwrites the current password stored in the I2C password
+                    register
+                  - Requires the device to be unlocked before changing the
+                    password
+                  - If the device is locked, the write silently fails
+
+What:           /sys/bus/i2c/devices/<busnum>-<primary-addr>/uid
+Date:           2025-07-04
+KernelVersion:  6.17
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
+Description:
+                Read-only attribute that exposes the 8-byte unique identifier
+                programmed into the M24LR chip at the factory.
+
+                Format:
+                  - Lowercase hexadecimal string representing a 64-bit value
+                  - 1 to 16 hex digits (e.g., "e00204f12345678")
+                  - No "0x" prefix
+                  - Includes a trailing newline
+
+What:           /sys/bus/i2c/devices/<busnum>-<primary-addr>/total_sectors
+Date:           2025-07-04
+KernelVersion:  6.17
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
+Description:
+                Read-only attribute that exposes the total number of EEPROM
+                sectors available in the M24LR chip.
+
+                Format:
+                  - 1 to 2 hex digits (e.g. "F")
+                  - No "0x" prefix
+                  - Includes a trailing newline
+
+                Notes:
+                  - Value is encoded by the chip and corresponds to the EEPROM
+                    size (e.g., 3 = 4 kbit for M24LR04E-R)
+
+What:           /sys/bus/i2c/devices/<busnum>-<primary-addr>/sss
+Date:           2025-07-04
+KernelVersion:  6.17
+Contact:        Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
+Description:
+                Read/write binary attribute representing the Sector Security
+                Status (SSS) bytes for all EEPROM sectors in STMicroelectronics
+                M24LR chips.
+
+                Each EEPROM sector has one SSS byte, which controls I2C and
+                RF access through protection bits and optional password
+                authentication.
+
+                Format:
+                  - The file contains one byte per EEPROM sector
+                  - Byte at offset N corresponds to sector N
+                  - Binary access only; use tools like dd, Python, or C that
+                    support byte-level I/O and offset control.
+
+                Notes:
+                  - The number of valid bytes in this file is equal to the
+                    value exposed by 'total_sectors' file
+                  - Write access requires prior password authentication in
+                    I2C mode
+                  - Refer to the M24LR datasheet for full SSS bit layout
-- 
2.43.0

Re: [PATCH v5 2/3] eeprom: add driver for ST M24LR series RFID/NFC EEPROM chips

[Christophe JAILLET]

Le 04/07/2025 à 14:39, Abd-Alrhman Masalkhi a écrit :
> adds support for STMicroelectronics M24LRxx devices, which expose
> two separate I2C addresses: one for system control and one for EEPROM
> access. The driver implements both a sysfs-based interface for control
> registers (e.g. UID, password authentication) and an nvmem provider
> for EEPROM access.

Hi, some nitpicks below, mostly related to types.

...

> +#include <linux/i2c.h>
> +#include <linux/regmap.h>
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/nvmem-provider.h>

Sometimes, alphabetical order is preferred.

> +
> +#define M24LR_WRITE_TIMEOUT	  25u
> +#define M24LR_READ_TIMEOUT	  (M24LR_WRITE_TIMEOUT)

...

> +/**
> + * m24lr_regmap_read - read data using regmap with retry on failure
> + * @regmap:  regmap instance for the device
> + * @buf:     buffer to store the read data
> + * @size:    number of bytes to read
> + * @offset:  starting register address
> + *
> + * Attempts to read a block of data from the device with retries and timeout.
> + * Some M24LR chips may transiently NACK reads (e.g., during internal write
> + * cycles), so this function retries with a short sleep until the timeout
> + * expires.
> + *
> + * Returns:
> + *	 Number of bytes read on success,
> + *	 -ETIMEDOUT if the read fails within the timeout window.
> + */
> +static ssize_t m24lr_regmap_read(struct regmap *regmap, u8 *buf,
> +				 size_t size, unsigned int offset)

Why returning a ssize_t?
regmap_bulk_read() returns an int.

> +{
> +	int err;
> +	unsigned long timeout, read_time;
> +	ssize_t ret = -ETIMEDOUT;
> +
> +	timeout = jiffies + msecs_to_jiffies(M24LR_READ_TIMEOUT);
> +	do {
> +		read_time = jiffies;
> +
> +		err = regmap_bulk_read(regmap, offset, buf, size);
> +		if (!err) {
> +			ret = size;
> +			break;
> +		}
> +
> +		usleep_range(1000, 2000);
> +	} while (time_before(read_time, timeout));
> +
> +	return ret;
> +}
...

> +static ssize_t m24lr_read(struct m24lr *m24lr, u8 *buf, size_t size,
> +			  unsigned int offset, bool is_eeprom)
> +{
> +	struct regmap *regmap;
> +	long ret;

Why long?
m24lr_regmap_read() returns a ssize_t. (+ see comment there for why a 
ssize_t)

(same comment applies to several places)

> +
> +	if (is_eeprom)
> +		regmap = m24lr->eeprom_regmap;
> +	else
> +		regmap = m24lr->ctl_regmap;
> +
> +	mutex_lock(&m24lr->lock);
> +	ret = m24lr_regmap_read(regmap, buf, size, offset);
> +	mutex_unlock(&m24lr->lock);
> +
> +	return ret;
> +}
> +
> +/**
> + * m24lr_write - write buffer to M24LR device with page alignment handling
> + * @m24lr:     pointer to driver context
> + * @buf:       data buffer to write
> + * @size:      number of bytes to write
> + * @offset:    target register address in the device
> + * @is_eeprom: true if the write should target the EEPROM,
> + *             false if it should target the system parameters sector.
> + *
> + * Writes data to the M24LR device using regmap, split into chunks no larger
> + * than page_size to respect device-specific write limitations (e.g., page
> + * size or I2C hold-time concerns). Each chunk is aligned to the page boundary
> + * defined by page_size.
> + *
> + * Returns:
> + *	 Total number of bytes written on success,
> + *	 A negative error code if any write fails.
> + */
> +static ssize_t m24lr_write(struct m24lr *m24lr, const u8 *buf, size_t size,
> +			   unsigned int offset, bool is_eeprom)
> +{
> +	unsigned int n, next_sector;
> +	struct regmap *regmap;
> +	ssize_t ret = 0;
> +	long err;
> +
> +	if (is_eeprom)
> +		regmap = m24lr->eeprom_regmap;
> +	else
> +		regmap = m24lr->ctl_regmap;
> +
> +	n = min(size, m24lr->page_size);

min_t()?

> +	next_sector = roundup(offset + 1, m24lr->page_size);
> +	if (offset + n > next_sector)
> +		n = next_sector - offset;
> +
> +	mutex_lock(&m24lr->lock);
> +	while (n) {
> +		err = m24lr_regmap_write(regmap, buf, n, offset);
> +		if (IS_ERR_VALUE(err)) {
> +			mutex_unlock(&m24lr->lock);
> +			if (ret)
> +				return ret;
> +			else

Unneeded else.

> +				return err;
> +		}
> +
> +		offset += n;
> +		size -= n;
> +		ret += n;
> +		n = min(size, m24lr->page_size);

min_t()?
Or change the type of page_size?

> +	}
> +	mutex_unlock(&m24lr->lock);
> +
> +	return ret;
> +}
> +
> +/**
> + * m24lr_write_pass - Write password to M24LR043-R using secure format
> + * @m24lr: Pointer to device control structure
> + * @buf:   Input buffer containing hex-encoded password
> + * @count: Number of bytes in @buf
> + * @code:  Operation code to embed between password copies
> + *
> + * This function parses a 4-byte password, encodes it in  big-endian format,
> + * and constructs a 9-byte sequence of the form:
> + *
> + *	  [BE(password), code, BE(password)]
> + *
> + * The result is written to register 0x0900 (2304), which is the password
> + * register in M24LR04E-R chip.
> + *
> + * Return: Number of bytes written on success, or negative error code on failure
> + */
> +static ssize_t m24lr_write_pass(struct m24lr *m24lr, const char *buf,
> +				size_t count, u8 code)
> +{
> +	__be32 be_pass;
> +	u8 output[9];
> +	long ret;

long vs ssize_t vs int.

> +	u32 pass;
> +	int err;
> +
> +	if (!count)
> +		return -EINVAL;
> +
> +	if (count > 8)
> +		return -EINVAL;
> +
> +	err = kstrtou32(buf, 16, &pass);
> +	if (err)
> +		return err;
> +
> +	be_pass = cpu_to_be32(pass);
> +
> +	memcpy(output, &be_pass, sizeof(be_pass));
> +	output[4] = code;
> +	memcpy(output + 5, &be_pass, sizeof(be_pass));
> +
> +	mutex_lock(&m24lr->lock);
> +	ret = m24lr_regmap_write(m24lr->ctl_regmap, output, 9, 2304);
> +	mutex_unlock(&m24lr->lock);
> +
> +	return ret;
> +}
> +
> +static ssize_t m24lr_read_reg_le(struct m24lr *m24lr, u64 *val,
> +				 unsigned int reg_addr,
> +				 unsigned int reg_size)
> +{
> +	long ret;

same

> +	__le64 input = 0;
> +
> +	ret = m24lr_read(m24lr, (u8 *)&input, reg_size, reg_addr, false);
> +	if (IS_ERR_VALUE(ret))
> +		return ret;
> +
> +	if (ret != reg_size)
> +		return -EINVAL;
> +
> +	switch (reg_size) {
> +	case 1:
> +		*val = *(u8 *)&input;
> +		break;
> +	case 2:
> +		*val = le16_to_cpu((__le16)input);
> +		break;
> +	case 4:
> +		*val = le32_to_cpu((__le32)input);
> +		break;
> +	case 8:
> +		*val = le64_to_cpu((__le64)input);
> +		break;
> +	default:
> +		return -EINVAL;
> +	};
> +
> +	return 0;
> +}
> +
> +static int m24lr_nvmem_read(void *priv, unsigned int offset, void *val,
> +			    size_t bytes)
> +{
> +	struct m24lr *m24lr = priv;
> +
> +	if (!bytes)
> +		return bytes;
> +
> +	if (offset + bytes > m24lr->eeprom_size)
> +		return -EINVAL;
> +
> +	return m24lr_read(m24lr, val, bytes, offset, true);

We return an int now?

> +}

...

> +static ssize_t m24lr_ctl_sss_read(struct file *filep, struct kobject *kobj,
> +				  const struct bin_attribute *attr, char *buf,
> +				  loff_t offset, size_t count)
> +{
> +	struct m24lr *m24lr = attr->private;
> +
> +	if (!count)
> +		return count;
> +
> +	if (offset + count > m24lr->sss_len)

Does using size_add() would make sense?

> +		return -EINVAL;
> +
> +	return m24lr_read(m24lr, buf, count, offset, false);
> +}
> +
> +static ssize_t m24lr_ctl_sss_write(struct file *filep, struct kobject *kobj,
> +				   const struct bin_attribute *attr, char *buf,
> +				   loff_t offset, size_t count)
> +{
> +	struct m24lr *m24lr = attr->private;
> +
> +	if (!count)
> +		return -EINVAL;
> +
> +	if (offset + count > m24lr->sss_len)

Same

> +		return -EINVAL;
> +
> +	return m24lr_write(m24lr, buf, count, offset, false);
> +}
> +static BIN_ATTR(sss, 0600, m24lr_ctl_sss_read, m24lr_ctl_sss_write, 0);

...

> +static struct attribute *m24lr_ctl_dev_attrs[] = {
> +	&dev_attr_unlock.attr,
> +	&dev_attr_new_pass.attr,
> +	&dev_attr_uid.attr,
> +	&dev_attr_total_sectors.attr,
> +	NULL,

Unneeded trailing ,

> +};

...

> +static int m24lr_probe(struct i2c_client *client)
> +{
> +	struct regmap_config eeprom_regmap_conf = {0};
> +	struct nvmem_config nvmem_conf = {0};
> +	struct device *dev = &client->dev;
> +	struct i2c_client *eeprom_client;
> +	const struct m24lr_chip *chip;
> +	struct regmap *eeprom_regmap;
> +	struct nvmem_device *nvmem;
> +	struct regmap *ctl_regmap;
> +	struct m24lr *m24lr;
> +	u32 regs[2];
> +	long err;
> +
> +	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
> +		return -EOPNOTSUPP;
> +
> +	chip = m24lr_get_chip(dev);
> +	if (!chip)
> +		return -ENODEV;
> +
> +	m24lr = devm_kzalloc(dev, sizeof(struct m24lr), GFP_KERNEL);
> +	if (!m24lr)
> +		return -ENOMEM;
> +
> +	err = device_property_read_u32_array(dev, "reg", regs, ARRAY_SIZE(regs));
> +	if (err) {
> +		dev_err(dev, "device_property_read_u32_array\n");

return dev_err_probe() maybe?

> +		return err;
> +	}
> +	/* Create a second I2C client for the eeprom interface */
> +	eeprom_client = devm_i2c_new_dummy_device(dev, client->adapter, regs[1]);
> +	if (IS_ERR(eeprom_client)) {
> +		dev_err(dev,
> +			"Failed to create dummy I2C client for the EEPROM\n");

return dev_err_probe() maybe?
...

> +		return PTR_ERR(eeprom_client);
> +	}
> +
> +	ctl_regmap = devm_regmap_init_i2c(client, &m24lr_ctl_regmap_conf);
> +	if (IS_ERR(ctl_regmap)) {
> +		err = PTR_ERR(ctl_regmap);
> +		dev_err(dev, "Failed to init regmap\n");
> +		return err;
> +	}
> +
> +	eeprom_regmap_conf.name = "m24lr_eeprom";
> +	eeprom_regmap_conf.reg_bits = 16;
> +	eeprom_regmap_conf.val_bits = 8;
> +	eeprom_regmap_conf.disable_locking = true;
> +	eeprom_regmap_conf.max_register = chip->eeprom_size - 1;
> +
> +	eeprom_regmap = devm_regmap_init_i2c(eeprom_client,
> +					     &eeprom_regmap_conf);
> +	if (IS_ERR(eeprom_regmap)) {
> +		err = PTR_ERR(eeprom_regmap);
> +		dev_err(dev, "Failed to init regmap\n");
> +		return err;
> +	}
> +
> +	mutex_init(&m24lr->lock);
> +	m24lr->sss_len = chip->sss_len;
> +	m24lr->page_size = chip->page_size;
> +	m24lr->eeprom_size = chip->eeprom_size;
> +	m24lr->eeprom_regmap = eeprom_regmap;
> +	m24lr->ctl_regmap = ctl_regmap;
> +
> +	nvmem_conf.dev = &eeprom_client->dev;
> +	nvmem_conf.owner = THIS_MODULE;
> +	nvmem_conf.type = NVMEM_TYPE_EEPROM;
> +	nvmem_conf.reg_read = m24lr_nvmem_read;
> +	nvmem_conf.reg_write = m24lr_nvmem_write;
> +	nvmem_conf.size = chip->eeprom_size;
> +	nvmem_conf.word_size = 1;
> +	nvmem_conf.stride = 1;
> +	nvmem_conf.priv = m24lr;
> +
> +	nvmem = devm_nvmem_register(dev, &nvmem_conf);
> +	if (IS_ERR(nvmem))
> +		return PTR_ERR(nvmem);
> +
> +	i2c_set_clientdata(client, m24lr);
> +	i2c_set_clientdata(eeprom_client, m24lr);
> +
> +	bin_attr_sss.size = chip->sss_len;
> +	bin_attr_sss.private = m24lr;
> +	err = sysfs_create_bin_file(&dev->kobj, &bin_attr_sss);
> +	if (err)
> +		return err;
> +
> +	/* test by reading the uid, if success store it */
> +	err = m24lr_read_reg_le(m24lr, &m24lr->uid, 2324, sizeof(m24lr->uid));
> +	if (IS_ERR_VALUE(err))

Missing sysfs_remove_bin_file() or error handling pah?

> +		return -ENODEV;
> +
> +	return 0;
> +}

...

CJ

Re: [PATCH v5 2/3] eeprom: add driver for ST M24LR series RFID/NFC EEPROM chips

[Abd-Alrhman Masalkhi]

On Fri, 4 Jul 2025 16:12:56 +0200, Christophe JAILLET wrote:
> Hi, some nitpicks below, mostly related to types.
> 
> ...
> 
> > +#include <linux/i2c.h>
> > +#include <linux/regmap.h>
> > +#include <linux/module.h>
> > +#include <linux/device.h>
> > +#include <linux/of.h>
> > +#include <linux/of_device.h>
> > +#include <linux/nvmem-provider.h>
> 
> Sometimes, alphabetical order is preferred.
> 
> > +
> > +#define M24LR_WRITE_TIMEOUT	  25u
> > +#define M24LR_READ_TIMEOUT	  (M24LR_WRITE_TIMEOUT)
> 
> ...
> 
> > +/**
> > + * m24lr_regmap_read - read data using regmap with retry on failure
> > + * @regmap:  regmap instance for the device
> > + * @buf:     buffer to store the read data
> > + * @size:    number of bytes to read
> > + * @offset:  starting register address
> > + *
> > + * Attempts to read a block of data from the device with retries and timeout.
> > + * Some M24LR chips may transiently NACK reads (e.g., during internal write
> > + * cycles), so this function retries with a short sleep until the timeout
> > + * expires.
> > + *
> > + * Returns:
> > + *	 Number of bytes read on success,
> > + *	 -ETIMEDOUT if the read fails within the timeout window.
> > + */
> > +static ssize_t m24lr_regmap_read(struct regmap *regmap, u8 *buf,
> > +				 size_t size, unsigned int offset)
> 
> Why returning a ssize_t?
> regmap_bulk_read() returns an int.
> 
> > +{
> > +	int err;
> > +	unsigned long timeout, read_time;
> > +	ssize_t ret = -ETIMEDOUT;
> > +
> > +	timeout = jiffies + msecs_to_jiffies(M24LR_READ_TIMEOUT);
> > +	do {
> > +		read_time = jiffies;
> > +
> > +		err = regmap_bulk_read(regmap, offset, buf, size);
> > +		if (!err) {
> > +			ret = size;
> > +			break;
> > +		}
> > +
> > +		usleep_range(1000, 2000);
> > +	} while (time_before(read_time, timeout));
> > +
> > +	return ret;
> > +}
> ...
> 
> > +static ssize_t m24lr_read(struct m24lr *m24lr, u8 *buf, size_t size,
> > +			  unsigned int offset, bool is_eeprom)
> > +{
> > +	struct regmap *regmap;
> > +	long ret;
> 
> Why long?
> m24lr_regmap_read() returns a ssize_t. (+ see comment there for why a 
> ssize_t)
> 
> (same comment applies to several places)
> 
> > +
> > +	if (is_eeprom)
> > +		regmap = m24lr->eeprom_regmap;
> > +	else
> > +		regmap = m24lr->ctl_regmap;
> > +
> > +	mutex_lock(&m24lr->lock);
> > +	ret = m24lr_regmap_read(regmap, buf, size, offset);
> > +	mutex_unlock(&m24lr->lock);
> > +
> > +	return ret;
> > +}
> > +
> > +/**
> > + * m24lr_write - write buffer to M24LR device with page alignment handling
> > + * @m24lr:     pointer to driver context
> > + * @buf:       data buffer to write
> > + * @size:      number of bytes to write
> > + * @offset:    target register address in the device
> > + * @is_eeprom: true if the write should target the EEPROM,
> > + *             false if it should target the system parameters sector.
> > + *
> > + * Writes data to the M24LR device using regmap, split into chunks no larger
> > + * than page_size to respect device-specific write limitations (e.g., page
> > + * size or I2C hold-time concerns). Each chunk is aligned to the page boundary
> > + * defined by page_size.
> > + *
> > + * Returns:
> > + *	 Total number of bytes written on success,
> > + *	 A negative error code if any write fails.
> > + */
> > +static ssize_t m24lr_write(struct m24lr *m24lr, const u8 *buf, size_t size,
> > +			   unsigned int offset, bool is_eeprom)
> > +{
> > +	unsigned int n, next_sector;
> > +	struct regmap *regmap;
> > +	ssize_t ret = 0;
> > +	long err;
> > +
> > +	if (is_eeprom)
> > +		regmap = m24lr->eeprom_regmap;
> > +	else
> > +		regmap = m24lr->ctl_regmap;
> > +
> > +	n = min(size, m24lr->page_size);
> 
> min_t()?
> 
> > +	next_sector = roundup(offset + 1, m24lr->page_size);
> > +	if (offset + n > next_sector)
> > +		n = next_sector - offset;
> > +
> > +	mutex_lock(&m24lr->lock);
> > +	while (n) {
> > +		err = m24lr_regmap_write(regmap, buf, n, offset);
> > +		if (IS_ERR_VALUE(err)) {
> > +			mutex_unlock(&m24lr->lock);
> > +			if (ret)
> > +				return ret;
> > +			else
> 
> Unneeded else.
> 
> > +				return err;
> > +		}
> > +
> > +		offset += n;
> > +		size -= n;
> > +		ret += n;
> > +		n = min(size, m24lr->page_size);
> 
> min_t()?
> Or change the type of page_size?
> 
> > +	}
> > +	mutex_unlock(&m24lr->lock);
> > +
> > +	return ret;
> > +}
> > +
> > +/**
> > + * m24lr_write_pass - Write password to M24LR043-R using secure format
> > + * @m24lr: Pointer to device control structure
> > + * @buf:   Input buffer containing hex-encoded password
> > + * @count: Number of bytes in @buf
> > + * @code:  Operation code to embed between password copies
> > + *
> > + * This function parses a 4-byte password, encodes it in  big-endian format,
> > + * and constructs a 9-byte sequence of the form:
> > + *
> > + *	  [BE(password), code, BE(password)]
> > + *
> > + * The result is written to register 0x0900 (2304), which is the password
> > + * register in M24LR04E-R chip.
> > + *
> > + * Return: Number of bytes written on success, or negative error code on failure
> > + */
> > +static ssize_t m24lr_write_pass(struct m24lr *m24lr, const char *buf,
> > +				size_t count, u8 code)
> > +{
> > +	__be32 be_pass;
> > +	u8 output[9];
> > +	long ret;
> 
> long vs ssize_t vs int.
> 
> > +	u32 pass;
> > +	int err;
> > +
> > +	if (!count)
> > +		return -EINVAL;
> > +
> > +	if (count > 8)
> > +		return -EINVAL;
> > +
> > +	err = kstrtou32(buf, 16, &pass);
> > +	if (err)
> > +		return err;
> > +
> > +	be_pass = cpu_to_be32(pass);
> > +
> > +	memcpy(output, &be_pass, sizeof(be_pass));
> > +	output[4] = code;
> > +	memcpy(output + 5, &be_pass, sizeof(be_pass));
> > +
> > +	mutex_lock(&m24lr->lock);
> > +	ret = m24lr_regmap_write(m24lr->ctl_regmap, output, 9, 2304);
> > +	mutex_unlock(&m24lr->lock);
> > +
> > +	return ret;
> > +}
> > +
> > +static ssize_t m24lr_read_reg_le(struct m24lr *m24lr, u64 *val,
> > +				 unsigned int reg_addr,
> > +				 unsigned int reg_size)
> > +{
> > +	long ret;
> 
> same
> 
> > +	__le64 input = 0;
> > +
> > +	ret = m24lr_read(m24lr, (u8 *)&input, reg_size, reg_addr, false);
> > +	if (IS_ERR_VALUE(ret))
> > +		return ret;
> > +
> > +	if (ret != reg_size)
> > +		return -EINVAL;
> > +
> > +	switch (reg_size) {
> > +	case 1:
> > +		*val = *(u8 *)&input;
> > +		break;
> > +	case 2:
> > +		*val = le16_to_cpu((__le16)input);
> > +		break;
> > +	case 4:
> > +		*val = le32_to_cpu((__le32)input);
> > +		break;
> > +	case 8:
> > +		*val = le64_to_cpu((__le64)input);
> > +		break;
> > +	default:
> > +		return -EINVAL;
> > +	};
> > +
> > +	return 0;
> > +}
> > +
> > +static int m24lr_nvmem_read(void *priv, unsigned int offset, void *val,
> > +			    size_t bytes)
> > +{
> > +	struct m24lr *m24lr = priv;
> > +
> > +	if (!bytes)
> > +		return bytes;
> > +
> > +	if (offset + bytes > m24lr->eeprom_size)
> > +		return -EINVAL;
> > +
> > +	return m24lr_read(m24lr, val, bytes, offset, true);
> 
> We return an int now?
> 
> > +}
> 
> ...
> 
> > +static ssize_t m24lr_ctl_sss_read(struct file *filep, struct kobject *kobj,
> > +				  const struct bin_attribute *attr, char *buf,
> > +				  loff_t offset, size_t count)
> > +{
> > +	struct m24lr *m24lr = attr->private;
> > +
> > +	if (!count)
> > +		return count;
> > +
> > +	if (offset + count > m24lr->sss_len)
> 
> Does using size_add() would make sense?
> 
> > +		return -EINVAL;
> > +
> > +	return m24lr_read(m24lr, buf, count, offset, false);
> > +}
> > +
> > +static ssize_t m24lr_ctl_sss_write(struct file *filep, struct kobject *kobj,
> > +				   const struct bin_attribute *attr, char *buf,
> > +				   loff_t offset, size_t count)
> > +{
> > +	struct m24lr *m24lr = attr->private;
> > +
> > +	if (!count)
> > +		return -EINVAL;
> > +
> > +	if (offset + count > m24lr->sss_len)
> 
> Same
> 
> > +		return -EINVAL;
> > +
> > +	return m24lr_write(m24lr, buf, count, offset, false);
> > +}
> > +static BIN_ATTR(sss, 0600, m24lr_ctl_sss_read, m24lr_ctl_sss_write, 0);
> 
> ...
> 
> > +static struct attribute *m24lr_ctl_dev_attrs[] = {
> > +	&dev_attr_unlock.attr,
> > +	&dev_attr_new_pass.attr,
> > +	&dev_attr_uid.attr,
> > +	&dev_attr_total_sectors.attr,
> > +	NULL,
> 
> Unneeded trailing ,
> 
> > +};
> 
> ...
> 
> > +static int m24lr_probe(struct i2c_client *client)
> > +{
> > +	struct regmap_config eeprom_regmap_conf = {0};
> > +	struct nvmem_config nvmem_conf = {0};
> > +	struct device *dev = &client->dev;
> > +	struct i2c_client *eeprom_client;
> > +	const struct m24lr_chip *chip;
> > +	struct regmap *eeprom_regmap;
> > +	struct nvmem_device *nvmem;
> > +	struct regmap *ctl_regmap;
> > +	struct m24lr *m24lr;
> > +	u32 regs[2];
> > +	long err;
> > +
> > +	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
> > +		return -EOPNOTSUPP;
> > +
> > +	chip = m24lr_get_chip(dev);
> > +	if (!chip)
> > +		return -ENODEV;
> > +
> > +	m24lr = devm_kzalloc(dev, sizeof(struct m24lr), GFP_KERNEL);
> > +	if (!m24lr)
> > +		return -ENOMEM;
> > +
> > +	err = device_property_read_u32_array(dev, "reg", regs, ARRAY_SIZE(regs));
> > +	if (err) {
> > +		dev_err(dev, "device_property_read_u32_array\n");
> 
> return dev_err_probe() maybe?
> 
> > +		return err;
> > +	}
> > +	/* Create a second I2C client for the eeprom interface */
> > +	eeprom_client = devm_i2c_new_dummy_device(dev, client->adapter, regs[1]);
> > +	if (IS_ERR(eeprom_client)) {
> > +		dev_err(dev,
> > +			"Failed to create dummy I2C client for the EEPROM\n");
> 
> return dev_err_probe() maybe?
> ...
> 
> > +		return PTR_ERR(eeprom_client);
> > +	}
> > +
> > +	ctl_regmap = devm_regmap_init_i2c(client, &m24lr_ctl_regmap_conf);
> > +	if (IS_ERR(ctl_regmap)) {
> > +		err = PTR_ERR(ctl_regmap);
> > +		dev_err(dev, "Failed to init regmap\n");
> > +		return err;
> > +	}
> > +
> > +	eeprom_regmap_conf.name = "m24lr_eeprom";
> > +	eeprom_regmap_conf.reg_bits = 16;
> > +	eeprom_regmap_conf.val_bits = 8;
> > +	eeprom_regmap_conf.disable_locking = true;
> > +	eeprom_regmap_conf.max_register = chip->eeprom_size - 1;
> > +
> > +	eeprom_regmap = devm_regmap_init_i2c(eeprom_client,
> > +					     &eeprom_regmap_conf);
> > +	if (IS_ERR(eeprom_regmap)) {
> > +		err = PTR_ERR(eeprom_regmap);
> > +		dev_err(dev, "Failed to init regmap\n");
> > +		return err;
> > +	}
> > +
> > +	mutex_init(&m24lr->lock);
> > +	m24lr->sss_len = chip->sss_len;
> > +	m24lr->page_size = chip->page_size;
> > +	m24lr->eeprom_size = chip->eeprom_size;
> > +	m24lr->eeprom_regmap = eeprom_regmap;
> > +	m24lr->ctl_regmap = ctl_regmap;
> > +
> > +	nvmem_conf.dev = &eeprom_client->dev;
> > +	nvmem_conf.owner = THIS_MODULE;
> > +	nvmem_conf.type = NVMEM_TYPE_EEPROM;
> > +	nvmem_conf.reg_read = m24lr_nvmem_read;
> > +	nvmem_conf.reg_write = m24lr_nvmem_write;
> > +	nvmem_conf.size = chip->eeprom_size;
> > +	nvmem_conf.word_size = 1;
> > +	nvmem_conf.stride = 1;
> > +	nvmem_conf.priv = m24lr;
> > +
> > +	nvmem = devm_nvmem_register(dev, &nvmem_conf);
> > +	if (IS_ERR(nvmem))
> > +		return PTR_ERR(nvmem);
> > +
> > +	i2c_set_clientdata(client, m24lr);
> > +	i2c_set_clientdata(eeprom_client, m24lr);
> > +
> > +	bin_attr_sss.size = chip->sss_len;
> > +	bin_attr_sss.private = m24lr;
> > +	err = sysfs_create_bin_file(&dev->kobj, &bin_attr_sss);
> > +	if (err)
> > +		return err;
> > +
> > +	/* test by reading the uid, if success store it */
> > +	err = m24lr_read_reg_le(m24lr, &m24lr->uid, 2324, sizeof(m24lr->uid));
> > +	if (IS_ERR_VALUE(err))
> 
> Missing sysfs_remove_bin_file() or error handling pah?
> 
> > +		return -ENODEV;
> > +
> > +	return 0;
> > +}

Hi Christophe, 

Thank you for the review!

It is done.

Best regards,
Abd-Alrhman Masalkhi

Re: [PATCH v5 1/3] dt-bindings: eeprom: Add ST M24LR support

[Krzysztof Kozlowski]

On 04/07/2025 14:39, Abd-Alrhman Masalkhi wrote:
> Add support for STMicroelectronics M24LR RFID/NFC EEPROM chips.
> These devices use two I2C addresses: the primary address provides
> access to control and system parameter registers, while the
> secondary address is used for EEPROM access.
> 
> Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
> ---
> Changes in v5:
>  - No changes and already reviewed by Krzysztof Kozlowski
>  - Link to v4: https://lore.kernel.org/lkml/20250608182714.3359441-2-abd.masalkhi@gmail.com/

So you just ignore the tag?

<form letter>
This is a friendly reminder during the review process.

It looks like you received a tag and forgot to add it.

If you do not know the process, here is a short explanation:
Please add Acked-by/Reviewed-by/Tested-by tags when posting new versions
of patchset, under or above your Signed-off-by tag, unless patch changed
significantly (e.g. new properties added to the DT bindings). Tag is
"received", when provided in a message replied to you on the mailing
list. Tools like b4 can help here. However, there's no need to repost
patches *only* to add the tags. The upstream maintainer will do that for
tags received on the version they apply.

Please read:
https://elixir.bootlin.com/linux/v6.12-rc3/source/Documentation/process/submitting-patches.rst#L577

If a tag was not added on purpose, please state why and what changed.
</form letter>


Best regards,
Krzysztof

Re: [PATCH v5 2/3] eeprom: add driver for ST M24LR series RFID/NFC EEPROM chips

[Abd-Alrhman Masalkhi]

Hi Christophe,

Thank you for the review!

On Fri, 4 Jul 2025 16:12:56 +0200, Christophe JAILLET wrote:
> > +/**
> > + * m24lr_regmap_read - read data using regmap with retry on failure
> > + * @regmap:  regmap instance for the device
> > + * @buf:     buffer to store the read data
> > + * @size:    number of bytes to read
> > + * @offset:  starting register address
> > + *
> > + * Attempts to read a block of data from the device with retries and timeout.
> > + * Some M24LR chips may transiently NACK reads (e.g., during internal write
> > + * cycles), so this function retries with a short sleep until the timeout
> > + * expires.
> > + *
> > + * Returns:
> > + *	 Number of bytes read on success,
> > + *	 -ETIMEDOUT if the read fails within the timeout window.
> > + */
> > +static ssize_t m24lr_regmap_read(struct regmap *regmap, u8 *buf,
> > +				 size_t size, unsigned int offset)
> 
> Why returning a ssize_t?
> regmap_bulk_read() returns an int.

Since I return @size (of type size_t) on success, should I keep the
return type as ssize_t, or would it be better to change it to int
to match regmap_bulk_read()?

Best regards,
Abd-Alrhman Masalkhi

Re: [PATCH v5 1/3] dt-bindings: eeprom: Add ST M24LR support

[Abd-Alrhman Masalkhi]

On Fri, 4 Jul 2025 17:10:07 +0200, Krzysztof Kozlowski wrote:
> On 04/07/2025 14:39, Abd-Alrhman Masalkhi wrote:
> > Add support for STMicroelectronics M24LR RFID/NFC EEPROM chips.
> > These devices use two I2C addresses: the primary address provides
> > access to control and system parameter registers, while the
> > secondary address is used for EEPROM access.
> > 
> > Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
> > ---
> > Changes in v5:
> >  - No changes and already reviewed by Krzysztof Kozlowski
> >  - Link to v4: https://lore.kernel.org/lkml/20250608182714.3359441-2-abd.masalkhi@gmail.com/
> 
> So you just ignore the tag?
> 
> <form letter>
> This is a friendly reminder during the review process.
> 
> It looks like you received a tag and forgot to add it.
> 
> If you do not know the process, here is a short explanation:
> Please add Acked-by/Reviewed-by/Tested-by tags when posting new versions
> of patchset, under or above your Signed-off-by tag, unless patch changed
> significantly (e.g. new properties added to the DT bindings). Tag is
> "received", when provided in a message replied to you on the mailing
> list. Tools like b4 can help here. However, there's no need to repost
> patches *only* to add the tags. The upstream maintainer will do that for
> tags received on the version they apply.
> 
> Please read:
> https://elixir.bootlin.com/linux/v6.12-rc3/source/Documentation/process/submitting-patches.rst#L577
> 
> If a tag was not added on purpose, please state why and what changed.
> </form letter>

Hi Krzysztof,

Thank you for the clear explanation. I wasn't aware of the process,
I will make sure to include the tags properly in future versions.

Best regards,
Abd-Alrhman Masalkhi

Re: [PATCH v5 2/3] eeprom: add driver for ST M24LR series RFID/NFC EEPROM chips

[Christophe JAILLET]

Le 04/07/2025 à 17:11, Abd-Alrhman Masalkhi a écrit :
> Hi Christophe,
> 
> Thank you for the review!
> 
> On Fri, 4 Jul 2025 16:12:56 +0200, Christophe JAILLET wrote:
>>> +/**
>>> + * m24lr_regmap_read - read data using regmap with retry on failure
>>> + * @regmap:  regmap instance for the device
>>> + * @buf:     buffer to store the read data
>>> + * @size:    number of bytes to read
>>> + * @offset:  starting register address
>>> + *
>>> + * Attempts to read a block of data from the device with retries and timeout.
>>> + * Some M24LR chips may transiently NACK reads (e.g., during internal write
>>> + * cycles), so this function retries with a short sleep until the timeout
>>> + * expires.
>>> + *
>>> + * Returns:
>>> + *	 Number of bytes read on success,
>>> + *	 -ETIMEDOUT if the read fails within the timeout window.
>>> + */
>>> +static ssize_t m24lr_regmap_read(struct regmap *regmap, u8 *buf,
>>> +				 size_t size, unsigned int offset)
>>
>> Why returning a ssize_t?
>> regmap_bulk_read() returns an int.
> 
> Since I return @size (of type size_t) on success, should I keep the
> return type as ssize_t, or would it be better to change it to int
> to match regmap_bulk_read()?

Hmm, this ends being used with BIN_ATTR() in 
m24lr_ctl_sss_[read|write]() so it needs to keep with ssize_t.

CJ

> 
> Best regards,
> Abd-Alrhman Masalkhi
> 
> 

Re: [PATCH v5 2/3] eeprom: add driver for ST M24LR series RFID/NFC EEPROM chips

[Abd-Alrhman Masalkhi]

Hi Christophe

On Fri, 4 Jul 2025 20:40:51 +0200, Christophe JAILLET wrote:
>>>> +/**
>>>> + * m24lr_regmap_read - read data using regmap with retry on failure
>>>> + * @regmap:  regmap instance for the device
>>>> + * @buf:     buffer to store the read data
>>>> + * @size:    number of bytes to read
>>>> + * @offset:  starting register address
>>>> + *
>>>> + * Attempts to read a block of data from the device with retries and timeout.
>>>> + * Some M24LR chips may transiently NACK reads (e.g., during internal write
>>>> + * cycles), so this function retries with a short sleep until the timeout
>>>> + * expires.
>>>> + *
>>>> + * Returns:
>>>> + *	 Number of bytes read on success,
>>>> + *	 -ETIMEDOUT if the read fails within the timeout window.
>>>> + */
>>>> +static ssize_t m24lr_regmap_read(struct regmap *regmap, u8 *buf,
>>>> +				 size_t size, unsigned int offset)
>>>
>>> Why returning a ssize_t?
>>> regmap_bulk_read() returns an int.
>> 
>> Since I return @size (of type size_t) on success, should I keep the
>> return type as ssize_t, or would it be better to change it to int
>> to match regmap_bulk_read()?
>
> Hmm, this ends being used with BIN_ATTR() in 
> m24lr_ctl_sss_[read|write]() so it needs to keep with ssize_t.

Done.

Best regards,
Abd-Alrhman Masalkhi