[PATCH v5 0/5] Add support for AAEON SRG-IMX8P MCU

[PATCH v5 0/5] Add support for AAEON SRG-IMX8P MCU

[Thomas Perrot (Schneider Electric)]

This patch series introduces support for the AAEON SRG-IMX8P embedded
controller (MCU). The MCU is connected via I2C and provides GPIO and
watchdog functionality for the SRG-IMX8P board.

The series includes:
- Device tree binding for the MFD driver
- MFD driver that serves as the core driver for the MCU
- GPIO driver implementing the GPIO functionality
- Watchdog driver for system monitoring
- MAINTAINERS entry for the new drivers

The drivers follow the standard Linux kernel subsystem patterns, with
the MFD driver registering the sub-devices (GPIO and watchdog) which
are then handled by their respective subsystem drivers.

Signed-off-by: Thomas Perrot (Schneider Electric) <thomas.perrot@bootlin.com>
---
Changes in v5:
- mfd: use heap-allocated DMA-safe buffers for I2C transfers, replacing
  stack-allocated buffers in the regmap bus callbacks
- mfd: switch from REGCACHE_NONE to REGCACHE_MAPLE; add volatile_reg
  callback marking GPIO input read registers (opcode 0x72) as volatile;
  add max_register
- mfd: use PLATFORM_DEVID_AUTO instead of PLATFORM_DEVID_NONE
- mfd: use MFD_CELL_BASIC() macro for cell definitions
- mfd: use dev_err_probe() for regmap initialization error
- Link to v4: https://lore.kernel.org/r/20260324-dev-b4-aaeon-mcu-driver-v4-0-afb011df4794@bootlin.com

Changes in v4:
- mfd: switch to a custom regmap bus; remove aaeon_mcu_i2c_xfer() and the aaeon_mcu_dev struct
- mfd: locking delegated to regmap's built-in mutex; drop explicit mutex
- mfd: remove firmware version reading at probe time
- gpio, watchdog: use regmap_read()/regmap_write() via dev_get_regmap()
- include: replace aaeon_mcu_i2c_xfer() declaration with AAEON_MCU_REG() macro
- dt-bindings: remove unused label from example node
- Link to v3: https://lore.kernel.org/r/20260203-dev-b4-aaeon-mcu-driver-v3-0-0a19432076ac@bootlin.com

Changes in v3:
- Renamed SRG-IMX8PL to SRG-IMX8P
- dt-bindings: add gpio-controller properties as required
- mfd: move struct aaeon_mcu_dev from header to .c file (private)
- mfd: use guard(mutex) and devm_mutex_init() for cleanup
- mfd: firmware version log changed to dev_dbg()
- mfd: add select MFD_CORE to Kconfig
- Kconfig: add || COMPILE_TEST to all three drivers
- watchdog: add comments explaining hardware timeout and WDOG_HW_RUNNING
- watchdog: remove unused platform_set_drvdata()
- watchdog: add a function to query the status
- Link to v2: https://lore.kernel.org/r/20260123-dev-b4-aaeon-mcu-driver-v2-0-9f4c00bfb5cb@bootlin.com

Changes in v2:
- Fold GPIO and watchdog bindings into MFD binding
- Drop OF_GPIO dependency in GPIO Kconfig
- Use __set_bit/__clear_bit/__assign_bit instead of atomic variants
- Various driver cleanups and improvements
- Link to v1: https://lore.kernel.org/r/20251212-dev-b4-aaeon-mcu-driver-v1-0-6bd65bc8ef12@bootlin.com

---
Thomas Perrot (Schneider Electric) (5):
      dt-bindings: vendor-prefixes: Add AAEON vendor prefix
      dt-bindings: mfd: Add AAEON embedded controller
      mfd: aaeon: Add SRG-IMX8P MCU driver
      gpio: aaeon: Add GPIO driver for SRG-IMX8P MCU
      watchdog: aaeon: Add watchdog driver for SRG-IMX8P MCU

 .../bindings/mfd/aaeon,srg-imx8p-mcu.yaml          |  67 ++++++
 .../devicetree/bindings/vendor-prefixes.yaml       |   2 +
 MAINTAINERS                                        |  10 +
 drivers/gpio/Kconfig                               |   9 +
 drivers/gpio/Makefile                              |   1 +
 drivers/gpio/gpio-aaeon-mcu.c                      | 229 +++++++++++++++++++++
 drivers/mfd/Kconfig                                |  10 +
 drivers/mfd/Makefile                               |   1 +
 drivers/mfd/aaeon-mcu.c                            | 204 ++++++++++++++++++
 drivers/watchdog/Kconfig                           |  10 +
 drivers/watchdog/Makefile                          |   1 +
 drivers/watchdog/aaeon_mcu_wdt.c                   | 132 ++++++++++++
 include/linux/mfd/aaeon-mcu.h                      |  40 ++++
 13 files changed, 716 insertions(+)
---
base-commit: d358e5254674b70f34c847715ca509e46eb81e6f
change-id: 20251211-dev-b4-aaeon-mcu-driver-e0e89ebf4afb

Best regards,
-- 
Thomas Perrot (Schneider Electric) <thomas.perrot@bootlin.com>

[PATCH v5 1/5] dt-bindings: vendor-prefixes: Add AAEON vendor prefix

[Thomas Perrot (Schneider Electric)]

Add the AAEON vendor prefix to support the AAEON SRG-IMX8P MCU driver
devicetree bindings.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Thomas Perrot (Schneider Electric) <thomas.perrot@bootlin.com>
---
 Documentation/devicetree/bindings/vendor-prefixes.yaml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Documentation/devicetree/bindings/vendor-prefixes.yaml b/Documentation/devicetree/bindings/vendor-prefixes.yaml
index c7591b2aec2a..0f84ee93b3a8 100644
--- a/Documentation/devicetree/bindings/vendor-prefixes.yaml
+++ b/Documentation/devicetree/bindings/vendor-prefixes.yaml
@@ -32,6 +32,8 @@ patternProperties:
     description: 8devices, UAB
   "^9tripod,.*":
     description: Shenzhen 9Tripod Innovation and Development CO., LTD.
+  "^aaeon,.*":
+    description: AAEON
   "^abb,.*":
     description: ABB
   "^abilis,.*":

-- 
2.53.0

[PATCH v5 2/5] dt-bindings: mfd: Add AAEON embedded controller

[Thomas Perrot (Schneider Electric)]

Add device tree binding documentation for the AAEON embedded controller
(MCU). This microcontroller is found on AAEON embedded boards, it is
connected via I2C and provides GPIO control and a watchdog timer.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Thomas Perrot (Schneider Electric) <thomas.perrot@bootlin.com>
---
 .../bindings/mfd/aaeon,srg-imx8p-mcu.yaml          | 67 ++++++++++++++++++++++
 MAINTAINERS                                        |  6 ++
 2 files changed, 73 insertions(+)

diff --git a/Documentation/devicetree/bindings/mfd/aaeon,srg-imx8p-mcu.yaml b/Documentation/devicetree/bindings/mfd/aaeon,srg-imx8p-mcu.yaml
new file mode 100644
index 000000000000..034fb7b42551
--- /dev/null
+++ b/Documentation/devicetree/bindings/mfd/aaeon,srg-imx8p-mcu.yaml
@@ -0,0 +1,67 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mfd/aaeon,srg-imx8p-mcu.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: AAEON Embedded Controller
+
+maintainers:
+  - Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
+  - Thomas Perrot <thomas.perrot@bootlin.com>
+
+description:
+  AAEON embeds a microcontroller on Standard RISC Gateway with ARM i.MX8M Plus
+  Quad-Core boards providing GPIO control and watchdog timer.
+
+  This MCU is connected via I2C bus.
+
+  Its GPIO controller provides 7 GPOs and 12 GPIOs.
+
+  Its watchdog has a fixed maximum hardware heartbeat of 25 seconds and supports
+  a timeout of 240 seconds through automatic pinging.
+  The timeout is not programmable and cannot be changed via device tree properties.
+
+properties:
+  compatible:
+    const: aaeon,srg-imx8p-mcu
+
+  reg:
+    maxItems: 1
+
+  gpio-controller: true
+
+  "#gpio-cells":
+    const: 2
+
+  gpio-line-names:
+    minItems: 1
+    maxItems: 19
+
+required:
+  - compatible
+  - reg
+  - gpio-controller
+  - "#gpio-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      embedded-controller@62 {
+        compatible = "aaeon,srg-imx8p-mcu";
+        reg = <0x62>;
+
+        gpio-controller;
+        #gpio-cells = <2>;
+        gpio-line-names = "gpo-1", "gpo-2", "gpo-3", "gpo-4",
+                          "gpo-5", "gpo-6", "gpo-7",
+                          "gpio-1", "gpio-2", "gpio-3", "gpio-4",
+                          "gpio-5", "gpio-6", "gpio-7", "gpio-8",
+                          "gpio-9", "gpio-10", "gpio-11", "gpio-12";
+      };
+    };
diff --git a/MAINTAINERS b/MAINTAINERS
index c9e416ba74c6..ea9d55f76f35 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -186,6 +186,12 @@ W:	http://www.adaptec.com/
 F:	Documentation/scsi/aacraid.rst
 F:	drivers/scsi/aacraid/
 
+AAEON SRG-IMX8P CONTROLLER MFD DRIVER
+M:	Thomas Perrot <thomas.perrot@bootlin.com>
+R:	Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
+S:	Maintained
+F:	Documentation/devicetree/bindings/mfd/aaeon,srg-imx8p-mcu.yaml
+
 AAEON UPBOARD FPGA MFD DRIVER
 M:	Thomas Richard <thomas.richard@bootlin.com>
 S:	Maintained

-- 
2.53.0

[PATCH v5 3/5] mfd: aaeon: Add SRG-IMX8P MCU driver

[Thomas Perrot (Schneider Electric)]

Add Multi-Function Device (MFD) driver for the Aaeon SRG-IMX8P
embedded controller. This driver provides the core I2C communication
interface and registers child devices (GPIO and watchdog controllers).

The driver implements a custom regmap bus over I2C to match the MCU's
fixed 3-byte command format [opcode, arg, value]. Register addresses
are encoded as 16-bit values (opcode << 8 | arg) using the
AAEON_MCU_REG() macro defined in the shared header. The regmap
instance is shared with child drivers via dev_get_regmap(). Concurrent
I2C accesses from child drivers are serialized by regmap's built-in
locking.

I2C transfers use heap-allocated DMA-safe buffers rather than
stack-allocated ones, as required by I2C controllers that perform DMA.

Regmap caching is enabled (REGCACHE_MAPLE) with a volatile_reg
callback that marks GPIO input read registers (opcode 0x72) and the
watchdog status register (opcode 0x63, arg 0x02) as volatile. All
other registers written by the driver (GPIO direction,
GPO state, watchdog control) are stable and can be safely cached.

Co-developed-by: Jérémie Dautheribes (Schneider Electric) <jeremie.dautheribes@bootlin.com>
Signed-off-by: Jérémie Dautheribes (Schneider Electric) <jeremie.dautheribes@bootlin.com>
Signed-off-by: Thomas Perrot (Schneider Electric) <thomas.perrot@bootlin.com>
---
 MAINTAINERS                   |   2 +
 drivers/mfd/Kconfig           |  10 +++
 drivers/mfd/Makefile          |   1 +
 drivers/mfd/aaeon-mcu.c       | 204 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/mfd/aaeon-mcu.h |  40 +++++++++
 5 files changed, 257 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index ea9d55f76f35..f91b6a1826d0 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -191,6 +191,8 @@ M:	Thomas Perrot <thomas.perrot@bootlin.com>
 R:	Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
 S:	Maintained
 F:	Documentation/devicetree/bindings/mfd/aaeon,srg-imx8p-mcu.yaml
+F:	drivers/mfd/aaeon-mcu.c
+F:	include/linux/mfd/aaeon-mcu.h
 
 AAEON UPBOARD FPGA MFD DRIVER
 M:	Thomas Richard <thomas.richard@bootlin.com>
diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index aace5766b38a..82ec1d8e7224 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -1561,6 +1561,16 @@ config ABX500_CORE
 	  remain unchanged when IC changes. Binding of the functions to
 	  actual register access is done by the IC core driver.
 
+config MFD_AAEON_MCU
+	tristate "Aaeon SRG-IMX8P MCU Driver"
+	depends on I2C || COMPILE_TEST
+	select MFD_CORE
+	help
+	  Select this option to enable support for the Aaeon SRG-IMX8P
+	  onboard microcontroller (MCU). This driver provides the core
+	  functionality to communicate with the MCU over I2C. The MCU
+	  provides GPIO and watchdog functionality.
+
 config AB8500_CORE
 	bool "ST-Ericsson AB8500 Mixed Signal Power Management chip"
 	depends on ABX500_CORE && MFD_DB8500_PRCMU
diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
index e75e8045c28a..34db5b033584 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -8,6 +8,7 @@ obj-$(CONFIG_MFD_88PM860X)	+= 88pm860x.o
 obj-$(CONFIG_MFD_88PM800)	+= 88pm800.o 88pm80x.o
 obj-$(CONFIG_MFD_88PM805)	+= 88pm805.o 88pm80x.o
 obj-$(CONFIG_MFD_88PM886_PMIC)	+= 88pm886.o
+obj-$(CONFIG_MFD_AAEON_MCU)	+= aaeon-mcu.o
 obj-$(CONFIG_MFD_ACT8945A)	+= act8945a.o
 obj-$(CONFIG_MFD_SM501)		+= sm501.o
 obj-$(CONFIG_ARCH_BCM2835)	+= bcm2835-pm.o
diff --git a/drivers/mfd/aaeon-mcu.c b/drivers/mfd/aaeon-mcu.c
new file mode 100644
index 000000000000..3b4e2d891534
--- /dev/null
+++ b/drivers/mfd/aaeon-mcu.c
@@ -0,0 +1,204 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Aaeon MCU driver
+ *
+ * Copyright (C) 2026 Bootlin
+ * Author: Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
+ * Author: Thomas Perrot <thomas.perrot@bootlin.com>
+ */
+
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/mfd/aaeon-mcu.h>
+#include <linux/mfd/core.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+
+struct aaeon_mcu {
+	struct i2c_client *client;
+	u8 *cmd;      /* DMA-safe 3-byte write buffer [opcode, arg, value] */
+	u8 *response; /* DMA-safe 1-byte read buffer for MCU acknowledgment */
+};
+
+static const struct mfd_cell aaeon_mcu_devs[] = {
+	MFD_CELL_BASIC("aaeon-mcu-wdt", NULL, NULL, 0, 0),
+	MFD_CELL_BASIC("aaeon-mcu-gpio", NULL, NULL, 0, 0),
+};
+
+/* Number of bytes in a MCU command: [opcode, arg, value] */
+#define AAEON_MCU_CMD_LEN      3
+
+/*
+ * Custom regmap bus for the Aaeon MCU I2C protocol.
+ *
+ * The MCU uses a fixed 3-byte command format [opcode, arg, value] followed
+ * by a 1-byte response. It requires a STOP condition between the command
+ * write and the response read, so two separate i2c_transfer() calls are
+ * issued.  The regmap lock serialises concurrent accesses from the GPIO
+ * and watchdog child drivers.
+ *
+ * Register addresses are encoded as a 16-bit big-endian value where the
+ * high byte is the opcode and the low byte is the argument, matching the
+ * wire layout produced by regmap for reg_bits=16.
+ */
+
+static int aaeon_mcu_regmap_write(void *context, const void *data, size_t count)
+{
+	struct aaeon_mcu *mcu = context;
+	struct i2c_client *client = mcu->client;
+	struct i2c_msg write_msg;
+	/* The MCU always sends a response byte after each command; discard it. */
+	struct i2c_msg response_msg;
+	int ret;
+
+	memcpy(mcu->cmd, data, count);
+
+	write_msg.addr  = client->addr;
+	write_msg.flags = 0;
+	write_msg.buf   = mcu->cmd;
+	write_msg.len   = count;
+
+	response_msg.addr  = client->addr;
+	response_msg.flags = I2C_M_RD;
+	response_msg.buf   = mcu->response;
+	response_msg.len   = 1;
+
+	ret = i2c_transfer(client->adapter, &write_msg, 1);
+	if (ret < 0)
+		return ret;
+	if (ret != 1)
+		return -EIO;
+
+	ret = i2c_transfer(client->adapter, &response_msg, 1);
+	if (ret < 0)
+		return ret;
+	if (ret != 1)
+		return -EIO;
+
+	return 0;
+}
+
+static int aaeon_mcu_regmap_read(void *context, const void *reg_buf,
+				 size_t reg_size, void *val_buf, size_t val_size)
+{
+	struct aaeon_mcu *mcu = context;
+	struct i2c_client *client = mcu->client;
+	struct i2c_msg write_msg;
+	struct i2c_msg read_msg;
+	int ret;
+
+	/*
+	 * reg_buf holds the 2-byte big-endian register address [opcode, arg].
+	 * Append a trailing 0x00 to form the full 3-byte MCU command.
+	 */
+	mcu->cmd[0] = ((u8 *)reg_buf)[0];
+	mcu->cmd[1] = ((u8 *)reg_buf)[1];
+	mcu->cmd[2] = 0x00;
+
+	write_msg.addr  = client->addr;
+	write_msg.flags = 0;
+	write_msg.buf   = mcu->cmd;
+	write_msg.len   = AAEON_MCU_CMD_LEN;
+
+	read_msg.addr  = client->addr;
+	read_msg.flags = I2C_M_RD;
+	read_msg.buf   = val_buf;
+	read_msg.len   = val_size;
+
+	ret = i2c_transfer(client->adapter, &write_msg, 1);
+	if (ret < 0)
+		return ret;
+	if (ret != 1)
+		return -EIO;
+
+	ret = i2c_transfer(client->adapter, &read_msg, 1);
+	if (ret < 0)
+		return ret;
+	if (ret != 1)
+		return -EIO;
+
+	return 0;
+}
+
+static const struct regmap_bus aaeon_mcu_regmap_bus = {
+	.write = aaeon_mcu_regmap_write,
+	.read  = aaeon_mcu_regmap_read,
+};
+
+static bool aaeon_mcu_volatile_reg(struct device *dev, unsigned int reg)
+{
+	/*
+	 * GPIO input registers are driven by external signals and can change
+	 * at any time without CPU involvement, always read from hardware.
+	 *
+	 * The watchdog status register reflects hardware state and can change
+	 * autonomously.
+	 *
+	 * All other registers are written by the driver and their values are
+	 * stable, so they can be safely cached.
+	 */
+	if ((reg >> 8) == AAEON_MCU_READ_GPIO_OPCODE)
+		return true;
+	if (reg == AAEON_MCU_REG(AAEON_MCU_CONTROL_WDT_OPCODE, 0x02))
+		return true;
+	return false;
+}
+
+static const struct regmap_config aaeon_mcu_regmap_config = {
+	.reg_bits          = 16,
+	.val_bits          = 8,
+	.reg_format_endian = REGMAP_ENDIAN_BIG,
+	.max_register      = AAEON_MCU_MAX_REGISTER,
+	.volatile_reg      = aaeon_mcu_volatile_reg,
+	.cache_type        = REGCACHE_MAPLE,
+};
+
+static int aaeon_mcu_probe(struct i2c_client *client)
+{
+	struct aaeon_mcu *mcu;
+	struct regmap *regmap;
+
+	mcu = devm_kzalloc(&client->dev, sizeof(*mcu), GFP_KERNEL);
+	if (!mcu)
+		return -ENOMEM;
+
+	mcu->client = client;
+
+	mcu->cmd = devm_kzalloc(&client->dev, AAEON_MCU_CMD_LEN * sizeof(*mcu->cmd), GFP_KERNEL);
+	if (!mcu->cmd)
+		return -ENOMEM;
+
+	mcu->response = devm_kzalloc(&client->dev, sizeof(*mcu->response), GFP_KERNEL);
+	if (!mcu->response)
+		return -ENOMEM;
+
+	regmap = devm_regmap_init(&client->dev, &aaeon_mcu_regmap_bus,
+				  mcu, &aaeon_mcu_regmap_config);
+	if (IS_ERR(regmap))
+		return dev_err_probe(&client->dev, PTR_ERR(regmap),
+				     "failed to initialize regmap\n");
+
+	return devm_mfd_add_devices(&client->dev, PLATFORM_DEVID_AUTO,
+				    aaeon_mcu_devs, ARRAY_SIZE(aaeon_mcu_devs),
+				    NULL, 0, NULL);
+}
+
+static const struct of_device_id aaeon_mcu_of_match[] = {
+	{ .compatible = "aaeon,srg-imx8p-mcu" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, aaeon_mcu_of_match);
+
+static struct i2c_driver aaeon_mcu_driver = {
+	.driver = {
+		.name = "aaeon_mcu",
+		.of_match_table = aaeon_mcu_of_match,
+	},
+	.probe = aaeon_mcu_probe,
+};
+module_i2c_driver(aaeon_mcu_driver);
+
+MODULE_DESCRIPTION("Aaeon MCU Driver");
+MODULE_AUTHOR("Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/mfd/aaeon-mcu.h b/include/linux/mfd/aaeon-mcu.h
new file mode 100644
index 000000000000..3a1aeec85d60
--- /dev/null
+++ b/include/linux/mfd/aaeon-mcu.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Aaeon MCU driver definitions
+ *
+ * Copyright (C) 2026 Bootlin
+ * Author: Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
+ * Author: Thomas Perrot <thomas.perrot@bootlin.com>
+ */
+
+#ifndef __LINUX_MFD_AAEON_MCU_H
+#define __LINUX_MFD_AAEON_MCU_H
+
+/*
+ * MCU register address: the high byte is the command opcode, the low
+ * byte is the argument.  This matches the 3-byte wire format
+ * [opcode, arg, value] used by the MCU I2C protocol.
+ */
+#define AAEON_MCU_REG(op, arg)		(((op) << 8) | (arg))
+
+/*
+ * Opcode for GPIO input reads. These registers are volatile, their values
+ * are driven by external signals and can change without CPU involvement.
+ * Used by the MFD driver's volatile_reg callback to bypass the regmap cache.
+ */
+#define AAEON_MCU_READ_GPIO_OPCODE	0x72
+
+/*
+ * Opcode for watchdog control and status commands.
+ * The status register (arg=0x02) reflects hardware state and is volatile.
+ */
+#define AAEON_MCU_CONTROL_WDT_OPCODE	0x63
+
+/*
+ * Highest register address in the MCU register map.
+ * The WRITE_GPIO opcode (0x77) with the highest GPIO argument (0x0B = 11,
+ * i.e. MAX_GPIOS - 1) produces the largest encoded address.
+ */
+#define AAEON_MCU_MAX_REGISTER		AAEON_MCU_REG(0x77, 0x0B)
+
+#endif /* __LINUX_MFD_AAEON_MCU_H */

-- 
2.53.0

[PATCH v5 4/5] gpio: aaeon: Add GPIO driver for SRG-IMX8P MCU

[Thomas Perrot (Schneider Electric)]

Add GPIO driver for the Aaeon SRG-IMX8P embedded controller. This
driver supports 7 GPO (General Purpose Output) pins and 12 GPIO pins
that can be configured as inputs or outputs.

The driver implements proper state management for GPO pins (which are
output-only) and full direction control for GPIO pins. During probe,
all pins are reset to a known state (GPOs low, GPIOs as inputs) to
prevent undefined behavior across system reboots, as the MCU does not
reset GPIO states on soft reboot.

Co-developed-by: Jérémie Dautheribes (Schneider Electric) <jeremie.dautheribes@bootlin.com>
Signed-off-by: Jérémie Dautheribes (Schneider Electric) <jeremie.dautheribes@bootlin.com>
Acked-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Thomas Perrot (Schneider Electric) <thomas.perrot@bootlin.com>
---
 MAINTAINERS                   |   1 +
 drivers/gpio/Kconfig          |   9 ++
 drivers/gpio/Makefile         |   1 +
 drivers/gpio/gpio-aaeon-mcu.c | 229 ++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 240 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index f91b6a1826d0..2538f8c4bc14 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -191,6 +191,7 @@ M:	Thomas Perrot <thomas.perrot@bootlin.com>
 R:	Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
 S:	Maintained
 F:	Documentation/devicetree/bindings/mfd/aaeon,srg-imx8p-mcu.yaml
+F:	drivers/gpio/gpio-aaeon-mcu.c
 F:	drivers/mfd/aaeon-mcu.c
 F:	include/linux/mfd/aaeon-mcu.h
 
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index c74da29253e8..4b37b5a15958 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -157,6 +157,15 @@ config GPIO_74XX_MMIO
 	    8 bits:	74244 (Input), 74273 (Output)
 	    16 bits:	741624 (Input), 7416374 (Output)
 
+config GPIO_AAEON_MCU
+	tristate "Aaeon MCU GPIO support"
+	depends on MFD_AAEON_MCU
+	help
+	  Select this option to enable GPIO support for the Aaeon SRG-IMX8P
+	  onboard MCU. This driver provides access to GPIO pins and GPO
+	  (General Purpose Output) pins controlled by the microcontroller.
+	  The driver handles both input and output configuration.
+
 config GPIO_ALTERA
 	tristate "Altera GPIO"
 	select GPIOLIB_IRQCHIP
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index 2421a8fd3733..1ba6318bc558 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -29,6 +29,7 @@ obj-$(CONFIG_GPIO_104_IDI_48)		+= gpio-104-idi-48.o
 obj-$(CONFIG_GPIO_104_IDIO_16)		+= gpio-104-idio-16.o
 obj-$(CONFIG_GPIO_74X164)		+= gpio-74x164.o
 obj-$(CONFIG_GPIO_74XX_MMIO)		+= gpio-74xx-mmio.o
+obj-$(CONFIG_GPIO_AAEON_MCU)		+= gpio-aaeon-mcu.o
 obj-$(CONFIG_GPIO_ADNP)			+= gpio-adnp.o
 obj-$(CONFIG_GPIO_ADP5520)		+= gpio-adp5520.o
 obj-$(CONFIG_GPIO_ADP5585)		+= gpio-adp5585.o
diff --git a/drivers/gpio/gpio-aaeon-mcu.c b/drivers/gpio/gpio-aaeon-mcu.c
new file mode 100644
index 000000000000..a37d3dc83795
--- /dev/null
+++ b/drivers/gpio/gpio-aaeon-mcu.c
@@ -0,0 +1,229 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Aaeon MCU GPIO driver
+ *
+ * Copyright (C) 2026 Bootlin
+ * Author: Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
+ * Author: Thomas Perrot <thomas.perrot@bootlin.com>
+ */
+
+#include <linux/bitops.h>
+#include <linux/gpio/driver.h>
+#include <linux/mfd/aaeon-mcu.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+#define AAEON_MCU_CONFIG_GPIO_INPUT	0x69
+#define AAEON_MCU_CONFIG_GPIO_OUTPUT	0x6F
+#define AAEON_MCU_READ_GPIO		0x72
+#define AAEON_MCU_WRITE_GPIO		0x77
+
+#define AAEON_MCU_CONTROL_GPO		0x6C
+
+#define MAX_GPIOS	12
+#define MAX_GPOS	7
+
+struct aaeon_mcu_gpio {
+	struct gpio_chip gc;
+	struct regmap *regmap;
+	DECLARE_BITMAP(dir_in, MAX_GPOS + MAX_GPIOS);
+	DECLARE_BITMAP(gpo_state, MAX_GPOS);
+};
+
+static int aaeon_mcu_gpio_config_input_cmd(struct aaeon_mcu_gpio *data,
+					   unsigned int offset)
+{
+	return regmap_write(data->regmap,
+			    AAEON_MCU_REG(AAEON_MCU_CONFIG_GPIO_INPUT, offset - 7),
+			    0);
+}
+
+static int aaeon_mcu_gpo_set_cmd(struct aaeon_mcu_gpio *data, unsigned int offset, int value)
+{
+	return regmap_write(data->regmap,
+			    AAEON_MCU_REG(AAEON_MCU_CONTROL_GPO, offset + 1),
+			    !!value);
+}
+
+static int aaeon_mcu_gpio_direction_input(struct gpio_chip *gc, unsigned int offset)
+{
+	struct aaeon_mcu_gpio *data = gpiochip_get_data(gc);
+	int ret;
+
+	if (offset < MAX_GPOS) {
+		dev_err(gc->parent,
+			"offset %d is a GPO (output-only) pin, cannot be configured as input\n",
+			offset);
+		return -EOPNOTSUPP;
+	}
+
+	ret = aaeon_mcu_gpio_config_input_cmd(data, offset);
+	if (ret < 0)
+		return ret;
+
+	__set_bit(offset, data->dir_in);
+
+	return 0;
+}
+
+static int aaeon_mcu_gpio_config_output_cmd(struct aaeon_mcu_gpio *data,
+					    unsigned int offset,
+					    int value)
+{
+	int ret;
+
+	ret = regmap_write(data->regmap,
+			   AAEON_MCU_REG(AAEON_MCU_CONFIG_GPIO_OUTPUT, offset - 7),
+			   0);
+	if (ret < 0)
+		return ret;
+
+	return regmap_write(data->regmap,
+			    AAEON_MCU_REG(AAEON_MCU_WRITE_GPIO, offset - 7),
+			    !!value);
+}
+
+static int aaeon_mcu_gpio_direction_output(struct gpio_chip *gc, unsigned int offset, int value)
+{
+	struct aaeon_mcu_gpio *data = gpiochip_get_data(gc);
+	int ret;
+
+	if (offset < MAX_GPOS) {
+		ret = aaeon_mcu_gpo_set_cmd(data, offset, value);
+		if (ret)
+			return ret;
+		__assign_bit(offset, data->gpo_state, value);
+		return 0;
+	}
+
+	ret = aaeon_mcu_gpio_config_output_cmd(data, offset, value);
+	if (ret < 0)
+		return ret;
+
+	__clear_bit(offset, data->dir_in);
+
+	return 0;
+}
+
+static int aaeon_mcu_gpio_get_direction(struct gpio_chip *gc, unsigned int offset)
+{
+	struct aaeon_mcu_gpio *data = gpiochip_get_data(gc);
+
+	return test_bit(offset, data->dir_in) ?
+		GPIO_LINE_DIRECTION_IN : GPIO_LINE_DIRECTION_OUT;
+}
+
+static int aaeon_mcu_gpio_get(struct gpio_chip *gc, unsigned int offset)
+{
+	struct aaeon_mcu_gpio *data = gpiochip_get_data(gc);
+	unsigned int rsp;
+	int ret;
+
+	if (offset < MAX_GPOS)
+		return test_bit(offset, data->gpo_state);
+
+	ret = regmap_read(data->regmap,
+			  AAEON_MCU_REG(AAEON_MCU_READ_GPIO, offset - 7),
+			  &rsp);
+	if (ret < 0)
+		return ret;
+
+	return rsp;
+}
+
+static int aaeon_mcu_gpio_set_cmd(struct aaeon_mcu_gpio *data, unsigned int offset, int value)
+{
+	return regmap_write(data->regmap,
+			    AAEON_MCU_REG(AAEON_MCU_WRITE_GPIO, offset - 7),
+			    !!value);
+}
+
+static int aaeon_mcu_gpio_set(struct gpio_chip *gc, unsigned int offset,
+			      int value)
+{
+	struct aaeon_mcu_gpio *data = gpiochip_get_data(gc);
+	int ret;
+
+	if (offset >= MAX_GPOS)
+		return aaeon_mcu_gpio_set_cmd(data, offset, value);
+
+	ret = aaeon_mcu_gpo_set_cmd(data, offset, value);
+	if (ret)
+		return ret;
+	__assign_bit(offset, data->gpo_state, value);
+	return 0;
+}
+
+static const struct gpio_chip aaeon_mcu_chip = {
+	.label			= "gpio-aaeon-mcu",
+	.owner			= THIS_MODULE,
+	.get_direction		= aaeon_mcu_gpio_get_direction,
+	.direction_input	= aaeon_mcu_gpio_direction_input,
+	.direction_output	= aaeon_mcu_gpio_direction_output,
+	.get			= aaeon_mcu_gpio_get,
+	.set			= aaeon_mcu_gpio_set,
+	.base			= -1,
+	.ngpio			= MAX_GPOS + MAX_GPIOS,
+	.can_sleep		= true,
+};
+
+static void aaeon_mcu_gpio_reset(struct aaeon_mcu_gpio *data, struct device *dev)
+{
+	unsigned int i;
+	int ret;
+
+	/* Reset all GPOs */
+	for (i = 0; i < MAX_GPOS; i++) {
+		ret = aaeon_mcu_gpo_set_cmd(data, i, 0);
+		if (ret < 0)
+			dev_warn(dev, "Failed to reset GPO %u state: %d\n", i, ret);
+		__clear_bit(i, data->dir_in);
+	}
+
+	/* Reset all GPIOs */
+	for (i = MAX_GPOS; i < MAX_GPOS + MAX_GPIOS; i++) {
+		ret = aaeon_mcu_gpio_config_input_cmd(data, i);
+		if (ret < 0)
+			dev_warn(dev, "Failed to reset GPIO %u state: %d\n", i, ret);
+		__set_bit(i, data->dir_in);
+	}
+}
+
+static int aaeon_mcu_gpio_probe(struct platform_device *pdev)
+{
+	struct aaeon_mcu_gpio *data;
+
+	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->regmap = dev_get_regmap(pdev->dev.parent, NULL);
+	if (!data->regmap)
+		return -ENODEV;
+
+	data->gc = aaeon_mcu_chip;
+	data->gc.parent = pdev->dev.parent;
+
+	/*
+	 * Reset all GPIO states to a known configuration. The MCU does not
+	 * reset GPIO state on soft reboot, only on power cycle (hard reboot).
+	 * Without this reset, GPIOs would retain their previous state across
+	 * reboots, which could lead to unexpected behavior.
+	 */
+	aaeon_mcu_gpio_reset(data, &pdev->dev);
+
+	return devm_gpiochip_add_data(&pdev->dev, &data->gc, data);
+}
+
+static struct platform_driver aaeon_mcu_gpio_driver = {
+	.driver = {
+		.name = "aaeon-mcu-gpio",
+	},
+	.probe = aaeon_mcu_gpio_probe,
+};
+module_platform_driver(aaeon_mcu_gpio_driver);
+
+MODULE_DESCRIPTION("GPIO interface for Aaeon MCU");
+MODULE_AUTHOR("Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>");
+MODULE_LICENSE("GPL");

-- 
2.53.0

[PATCH v5 5/5] watchdog: aaeon: Add watchdog driver for SRG-IMX8P MCU

[Thomas Perrot (Schneider Electric)]

Add watchdog driver for the Aaeon SRG-IMX8P embedded controller.
This driver provides system monitoring and recovery capabilities
through the MCU's watchdog timer.

The watchdog supports start, stop, and ping operations with a maximum
hardware heartbeat of 25 seconds and a default timeout of 240 seconds.

Co-developed-by: Jérémie Dautheribes (Schneider Electric) <jeremie.dautheribes@bootlin.com>
Signed-off-by: Jérémie Dautheribes (Schneider Electric) <jeremie.dautheribes@bootlin.com>
Signed-off-by: Thomas Perrot (Schneider Electric) <thomas.perrot@bootlin.com>
---
 MAINTAINERS                      |   1 +
 drivers/watchdog/Kconfig         |  10 +++
 drivers/watchdog/Makefile        |   1 +
 drivers/watchdog/aaeon_mcu_wdt.c | 132 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 144 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 2538f8c4bc14..7b92af42c9fd 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -193,6 +193,7 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/mfd/aaeon,srg-imx8p-mcu.yaml
 F:	drivers/gpio/gpio-aaeon-mcu.c
 F:	drivers/mfd/aaeon-mcu.c
+F:	drivers/watchdog/aaeon_mcu_wdt.c
 F:	include/linux/mfd/aaeon-mcu.h
 
 AAEON UPBOARD FPGA MFD DRIVER
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index d3b9df7d466b..f67a0b453316 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -420,6 +420,16 @@ config SL28CPLD_WATCHDOG
 
 # ARM Architecture
 
+config AAEON_MCU_WATCHDOG
+	tristate "Aaeon MCU Watchdog"
+	depends on MFD_AAEON_MCU
+	select WATCHDOG_CORE
+	help
+	  Select this option to enable watchdog timer support for the Aaeon
+	  SRG-IMX8P onboard microcontroller (MCU). This driver provides
+	  watchdog functionality through the MCU, allowing system monitoring
+	  and automatic recovery from system hangs.
+
 config AIROHA_WATCHDOG
 	tristate "Airoha EN7581 Watchdog"
 	depends on ARCH_AIROHA || COMPILE_TEST
diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index ba52099b1253..2deec425d3ea 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -37,6 +37,7 @@ obj-$(CONFIG_USBPCWATCHDOG) += pcwd_usb.o
 # ALPHA Architecture
 
 # ARM Architecture
+obj-$(CONFIG_AAEON_MCU_WATCHDOG) += aaeon_mcu_wdt.o
 obj-$(CONFIG_ARM_SP805_WATCHDOG) += sp805_wdt.o
 obj-$(CONFIG_ARM_SBSA_WATCHDOG) += sbsa_gwdt.o
 obj-$(CONFIG_ARMADA_37XX_WATCHDOG) += armada_37xx_wdt.o
diff --git a/drivers/watchdog/aaeon_mcu_wdt.c b/drivers/watchdog/aaeon_mcu_wdt.c
new file mode 100644
index 000000000000..949b506d8194
--- /dev/null
+++ b/drivers/watchdog/aaeon_mcu_wdt.c
@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Aaeon MCU Watchdog driver
+ *
+ * Copyright (C) 2026 Bootlin
+ * Author: Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
+ * Author: Thomas Perrot <thomas.perrot@bootlin.com>
+ */
+
+#include <linux/mfd/aaeon-mcu.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/watchdog.h>
+
+#define AAEON_MCU_PING_WDT	0x73
+
+#define AAEON_MCU_WDT_TIMEOUT         240
+#define AAEON_MCU_WDT_HEARTBEAT_MS    25000
+
+struct aaeon_mcu_wdt {
+	struct watchdog_device wdt;
+	struct regmap *regmap;
+};
+
+static int aaeon_mcu_wdt_cmd(struct aaeon_mcu_wdt *data, u8 opcode, u8 arg)
+{
+	return regmap_write(data->regmap, AAEON_MCU_REG(opcode, arg), 0);
+}
+
+static int aaeon_mcu_wdt_start(struct watchdog_device *wdt)
+{
+	struct aaeon_mcu_wdt *data = watchdog_get_drvdata(wdt);
+
+	return aaeon_mcu_wdt_cmd(data, AAEON_MCU_CONTROL_WDT_OPCODE, 0x01);
+}
+
+static int aaeon_mcu_wdt_status(struct watchdog_device *wdt, bool *enabled)
+{
+	struct aaeon_mcu_wdt *data = watchdog_get_drvdata(wdt);
+	unsigned int rsp;
+	int ret;
+
+	ret = regmap_read(data->regmap,
+			  AAEON_MCU_REG(AAEON_MCU_CONTROL_WDT_OPCODE, 0x02),
+			  &rsp);
+	if (ret)
+		return ret;
+
+	*enabled = rsp == 0x01;
+	return 0;
+}
+
+static int aaeon_mcu_wdt_stop(struct watchdog_device *wdt)
+{
+	struct aaeon_mcu_wdt *data = watchdog_get_drvdata(wdt);
+
+	return aaeon_mcu_wdt_cmd(data, AAEON_MCU_CONTROL_WDT_OPCODE, 0x00);
+}
+
+static int aaeon_mcu_wdt_ping(struct watchdog_device *wdt)
+{
+	struct aaeon_mcu_wdt *data = watchdog_get_drvdata(wdt);
+
+	return aaeon_mcu_wdt_cmd(data, AAEON_MCU_PING_WDT, 0x00);
+}
+
+static const struct watchdog_info aaeon_mcu_wdt_info = {
+	.identity	= "Aaeon MCU Watchdog",
+	.options	= WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE
+};
+
+static const struct watchdog_ops aaeon_mcu_wdt_ops = {
+	.owner		= THIS_MODULE,
+	.start		= aaeon_mcu_wdt_start,
+	.stop		= aaeon_mcu_wdt_stop,
+	.ping		= aaeon_mcu_wdt_ping,
+};
+
+static int aaeon_mcu_wdt_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct watchdog_device *wdt;
+	struct aaeon_mcu_wdt *data;
+	bool enabled;
+	int ret;
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->regmap = dev_get_regmap(dev->parent, NULL);
+	if (!data->regmap)
+		return -ENODEV;
+
+	wdt = &data->wdt;
+	wdt->parent = dev;
+	wdt->info = &aaeon_mcu_wdt_info;
+	wdt->ops = &aaeon_mcu_wdt_ops;
+	/*
+	 * The MCU firmware has a fixed hardware timeout of 25 seconds that
+	 * cannot be changed. The watchdog core will handle automatic pinging
+	 * to support longer timeouts. The software timeout of 240 seconds is
+	 * chosen arbitrarily as a reasonable value and is not user-configurable.
+	 */
+	wdt->timeout = AAEON_MCU_WDT_TIMEOUT;
+	wdt->max_hw_heartbeat_ms = AAEON_MCU_WDT_HEARTBEAT_MS;
+
+	watchdog_set_drvdata(wdt, data);
+
+	ret = aaeon_mcu_wdt_status(wdt, &enabled);
+	if (ret)
+		return ret;
+
+	if (enabled)
+		set_bit(WDOG_HW_RUNNING, &wdt->status);
+
+	return devm_watchdog_register_device(dev, wdt);
+}
+
+static struct platform_driver aaeon_mcu_wdt_driver = {
+	.driver		= {
+		.name	= "aaeon-mcu-wdt",
+	},
+	.probe		= aaeon_mcu_wdt_probe,
+};
+
+module_platform_driver(aaeon_mcu_wdt_driver);
+
+MODULE_DESCRIPTION("Aaeon MCU Watchdog Driver");
+MODULE_AUTHOR("Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>");
+MODULE_LICENSE("GPL");

-- 
2.53.0

Re: [PATCH v5 5/5] watchdog: aaeon: Add watchdog driver for SRG-IMX8P MCU

[Guenter Roeck]

On 4/8/26 10:21, Thomas Perrot (Schneider Electric) wrote:
> Add watchdog driver for the Aaeon SRG-IMX8P embedded controller.
> This driver provides system monitoring and recovery capabilities
> through the MCU's watchdog timer.
> 
> The watchdog supports start, stop, and ping operations with a maximum
> hardware heartbeat of 25 seconds and a default timeout of 240 seconds.
> 
> Co-developed-by: Jérémie Dautheribes (Schneider Electric) <jeremie.dautheribes@bootlin.com>
> Signed-off-by: Jérémie Dautheribes (Schneider Electric) <jeremie.dautheribes@bootlin.com>
> Signed-off-by: Thomas Perrot (Schneider Electric) <thomas.perrot@bootlin.com>
> ---
>   MAINTAINERS                      |   1 +
>   drivers/watchdog/Kconfig         |  10 +++
>   drivers/watchdog/Makefile        |   1 +
>   drivers/watchdog/aaeon_mcu_wdt.c | 132 +++++++++++++++++++++++++++++++++++++++
>   4 files changed, 144 insertions(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 2538f8c4bc14..7b92af42c9fd 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -193,6 +193,7 @@ S:	Maintained
>   F:	Documentation/devicetree/bindings/mfd/aaeon,srg-imx8p-mcu.yaml
>   F:	drivers/gpio/gpio-aaeon-mcu.c
>   F:	drivers/mfd/aaeon-mcu.c
> +F:	drivers/watchdog/aaeon_mcu_wdt.c
>   F:	include/linux/mfd/aaeon-mcu.h
>   
>   AAEON UPBOARD FPGA MFD DRIVER
> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> index d3b9df7d466b..f67a0b453316 100644
> --- a/drivers/watchdog/Kconfig
> +++ b/drivers/watchdog/Kconfig
> @@ -420,6 +420,16 @@ config SL28CPLD_WATCHDOG
>   
>   # ARM Architecture
>   
> +config AAEON_MCU_WATCHDOG
> +	tristate "Aaeon MCU Watchdog"
> +	depends on MFD_AAEON_MCU
> +	select WATCHDOG_CORE
> +	help
> +	  Select this option to enable watchdog timer support for the Aaeon
> +	  SRG-IMX8P onboard microcontroller (MCU). This driver provides
> +	  watchdog functionality through the MCU, allowing system monitoring
> +	  and automatic recovery from system hangs.
> +
>   config AIROHA_WATCHDOG
>   	tristate "Airoha EN7581 Watchdog"
>   	depends on ARCH_AIROHA || COMPILE_TEST
> diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> index ba52099b1253..2deec425d3ea 100644
> --- a/drivers/watchdog/Makefile
> +++ b/drivers/watchdog/Makefile
> @@ -37,6 +37,7 @@ obj-$(CONFIG_USBPCWATCHDOG) += pcwd_usb.o
>   # ALPHA Architecture
>   
>   # ARM Architecture
> +obj-$(CONFIG_AAEON_MCU_WATCHDOG) += aaeon_mcu_wdt.o
>   obj-$(CONFIG_ARM_SP805_WATCHDOG) += sp805_wdt.o
>   obj-$(CONFIG_ARM_SBSA_WATCHDOG) += sbsa_gwdt.o
>   obj-$(CONFIG_ARMADA_37XX_WATCHDOG) += armada_37xx_wdt.o
> diff --git a/drivers/watchdog/aaeon_mcu_wdt.c b/drivers/watchdog/aaeon_mcu_wdt.c
> new file mode 100644
> index 000000000000..949b506d8194
> --- /dev/null
> +++ b/drivers/watchdog/aaeon_mcu_wdt.c
> @@ -0,0 +1,132 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Aaeon MCU Watchdog driver
> + *
> + * Copyright (C) 2026 Bootlin
> + * Author: Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
> + * Author: Thomas Perrot <thomas.perrot@bootlin.com>
> + */
> +
> +#include <linux/mfd/aaeon-mcu.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/regmap.h>
> +#include <linux/watchdog.h>
> +
> +#define AAEON_MCU_PING_WDT	0x73
> +
> +#define AAEON_MCU_WDT_TIMEOUT         240
> +#define AAEON_MCU_WDT_HEARTBEAT_MS    25000
> +
> +struct aaeon_mcu_wdt {
> +	struct watchdog_device wdt;
> +	struct regmap *regmap;
> +};
> +
> +static int aaeon_mcu_wdt_cmd(struct aaeon_mcu_wdt *data, u8 opcode, u8 arg)
> +{
> +	return regmap_write(data->regmap, AAEON_MCU_REG(opcode, arg), 0);
> +}
> +
> +static int aaeon_mcu_wdt_start(struct watchdog_device *wdt)
> +{
> +	struct aaeon_mcu_wdt *data = watchdog_get_drvdata(wdt);
> +
> +	return aaeon_mcu_wdt_cmd(data, AAEON_MCU_CONTROL_WDT_OPCODE, 0x01);
> +}
> +
> +static int aaeon_mcu_wdt_status(struct watchdog_device *wdt, bool *enabled)
> +{
> +	struct aaeon_mcu_wdt *data = watchdog_get_drvdata(wdt);
> +	unsigned int rsp;
> +	int ret;
> +
> +	ret = regmap_read(data->regmap,
> +			  AAEON_MCU_REG(AAEON_MCU_CONTROL_WDT_OPCODE, 0x02),
> +			  &rsp);
> +	if (ret)
> +		return ret;
> +
> +	*enabled = rsp == 0x01;
> +	return 0;
> +}
> +
> +static int aaeon_mcu_wdt_stop(struct watchdog_device *wdt)
> +{
> +	struct aaeon_mcu_wdt *data = watchdog_get_drvdata(wdt);
> +
> +	return aaeon_mcu_wdt_cmd(data, AAEON_MCU_CONTROL_WDT_OPCODE, 0x00);
> +}
> +
> +static int aaeon_mcu_wdt_ping(struct watchdog_device *wdt)
> +{
> +	struct aaeon_mcu_wdt *data = watchdog_get_drvdata(wdt);
> +
> +	return aaeon_mcu_wdt_cmd(data, AAEON_MCU_PING_WDT, 0x00);
> +}
> +
> +static const struct watchdog_info aaeon_mcu_wdt_info = {
> +	.identity	= "Aaeon MCU Watchdog",
> +	.options	= WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE
> +};
> +
> +static const struct watchdog_ops aaeon_mcu_wdt_ops = {
> +	.owner		= THIS_MODULE,
> +	.start		= aaeon_mcu_wdt_start,
> +	.stop		= aaeon_mcu_wdt_stop,
> +	.ping		= aaeon_mcu_wdt_ping,
> +};
> +
> +static int aaeon_mcu_wdt_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct watchdog_device *wdt;
> +	struct aaeon_mcu_wdt *data;
> +	bool enabled;
> +	int ret;
> +
> +	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	data->regmap = dev_get_regmap(dev->parent, NULL);
> +	if (!data->regmap)
> +		return -ENODEV;
> +
> +	wdt = &data->wdt;
> +	wdt->parent = dev;
> +	wdt->info = &aaeon_mcu_wdt_info;
> +	wdt->ops = &aaeon_mcu_wdt_ops;
> +	/*
> +	 * The MCU firmware has a fixed hardware timeout of 25 seconds that
> +	 * cannot be changed. The watchdog core will handle automatic pinging
> +	 * to support longer timeouts. The software timeout of 240 seconds is
> +	 * chosen arbitrarily as a reasonable value and is not user-configurable.
> +	 */

Odd, unusual, unnecessary, I would argue that most people would consider a fixed
timeout of 240s as anything but reasonable, and as the comment says arbitrary.
Since I am sure that I pointed this out before, you still insist, and I am
tired of arguing: Your funeral, so

Acked-by: Guenter Roeck <linux@roeck-us.net>

Guenter

> +	wdt->timeout = AAEON_MCU_WDT_TIMEOUT;
> +	wdt->max_hw_heartbeat_ms = AAEON_MCU_WDT_HEARTBEAT_MS;
> +
> +	watchdog_set_drvdata(wdt, data);
> +
> +	ret = aaeon_mcu_wdt_status(wdt, &enabled);
> +	if (ret)
> +		return ret;
> +
> +	if (enabled)
> +		set_bit(WDOG_HW_RUNNING, &wdt->status);
> +
> +	return devm_watchdog_register_device(dev, wdt);
> +}
> +
> +static struct platform_driver aaeon_mcu_wdt_driver = {
> +	.driver		= {
> +		.name	= "aaeon-mcu-wdt",
> +	},
> +	.probe		= aaeon_mcu_wdt_probe,
> +};
> +
> +module_platform_driver(aaeon_mcu_wdt_driver);
> +
> +MODULE_DESCRIPTION("Aaeon MCU Watchdog Driver");
> +MODULE_AUTHOR("Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>");
> +MODULE_LICENSE("GPL");
> 

Re: [PATCH v5 0/5] Add support for AAEON SRG-IMX8P MCU

[Guenter Roeck]

On 4/8/26 10:21, Thomas Perrot (Schneider Electric) wrote:
> This patch series introduces support for the AAEON SRG-IMX8P embedded
> controller (MCU). The MCU is connected via I2C and provides GPIO and
> watchdog functionality for the SRG-IMX8P board.
> 
> The series includes:
> - Device tree binding for the MFD driver
> - MFD driver that serves as the core driver for the MCU
> - GPIO driver implementing the GPIO functionality
> - Watchdog driver for system monitoring
> - MAINTAINERS entry for the new drivers
> 
> The drivers follow the standard Linux kernel subsystem patterns, with
> the MFD driver registering the sub-devices (GPIO and watchdog) which
> are then handled by their respective subsystem drivers.
> 
> Signed-off-by: Thomas Perrot (Schneider Electric) <thomas.perrot@bootlin.com>

Sashiko has some interesting feedback that might be worth looking into.

https://sashiko.dev/#/patchset/20260408-dev-b4-aaeon-mcu-driver-v5-0-ad98bd481668%40bootlin.com

Guenter

Re: [PATCH v5 3/5] mfd: aaeon: Add SRG-IMX8P MCU driver

[Lee Jones]

On Wed, 08 Apr 2026, Thomas Perrot (Schneider Electric) wrote:

> Add Multi-Function Device (MFD) driver for the Aaeon SRG-IMX8P
> embedded controller. This driver provides the core I2C communication
> interface and registers child devices (GPIO and watchdog controllers).
> 
> The driver implements a custom regmap bus over I2C to match the MCU's
> fixed 3-byte command format [opcode, arg, value]. Register addresses
> are encoded as 16-bit values (opcode << 8 | arg) using the
> AAEON_MCU_REG() macro defined in the shared header. The regmap
> instance is shared with child drivers via dev_get_regmap(). Concurrent
> I2C accesses from child drivers are serialized by regmap's built-in
> locking.
> 
> I2C transfers use heap-allocated DMA-safe buffers rather than
> stack-allocated ones, as required by I2C controllers that perform DMA.
> 
> Regmap caching is enabled (REGCACHE_MAPLE) with a volatile_reg
> callback that marks GPIO input read registers (opcode 0x72) and the
> watchdog status register (opcode 0x63, arg 0x02) as volatile. All
> other registers written by the driver (GPIO direction,
> GPO state, watchdog control) are stable and can be safely cached.
> 
> Co-developed-by: Jérémie Dautheribes (Schneider Electric) <jeremie.dautheribes@bootlin.com>
> Signed-off-by: Jérémie Dautheribes (Schneider Electric) <jeremie.dautheribes@bootlin.com>
> Signed-off-by: Thomas Perrot (Schneider Electric) <thomas.perrot@bootlin.com>
> ---
>  MAINTAINERS                   |   2 +
>  drivers/mfd/Kconfig           |  10 +++
>  drivers/mfd/Makefile          |   1 +
>  drivers/mfd/aaeon-mcu.c       | 204 ++++++++++++++++++++++++++++++++++++++++++
>  include/linux/mfd/aaeon-mcu.h |  40 +++++++++
>  5 files changed, 257 insertions(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index ea9d55f76f35..f91b6a1826d0 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -191,6 +191,8 @@ M:	Thomas Perrot <thomas.perrot@bootlin.com>
>  R:	Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
>  S:	Maintained
>  F:	Documentation/devicetree/bindings/mfd/aaeon,srg-imx8p-mcu.yaml
> +F:	drivers/mfd/aaeon-mcu.c
> +F:	include/linux/mfd/aaeon-mcu.h
>  
>  AAEON UPBOARD FPGA MFD DRIVER
>  M:	Thomas Richard <thomas.richard@bootlin.com>
> diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
> index aace5766b38a..82ec1d8e7224 100644
> --- a/drivers/mfd/Kconfig
> +++ b/drivers/mfd/Kconfig
> @@ -1561,6 +1561,16 @@ config ABX500_CORE
>  	  remain unchanged when IC changes. Binding of the functions to
>  	  actual register access is done by the IC core driver.
>  
> +config MFD_AAEON_MCU
> +	tristate "Aaeon SRG-IMX8P MCU Driver"
> +	depends on I2C || COMPILE_TEST
> +	select MFD_CORE
> +	help
> +	  Select this option to enable support for the Aaeon SRG-IMX8P
> +	  onboard microcontroller (MCU). This driver provides the core
> +	  functionality to communicate with the MCU over I2C. The MCU
> +	  provides GPIO and watchdog functionality.
> +
>  config AB8500_CORE
>  	bool "ST-Ericsson AB8500 Mixed Signal Power Management chip"
>  	depends on ABX500_CORE && MFD_DB8500_PRCMU
> diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
> index e75e8045c28a..34db5b033584 100644
> --- a/drivers/mfd/Makefile
> +++ b/drivers/mfd/Makefile
> @@ -8,6 +8,7 @@ obj-$(CONFIG_MFD_88PM860X)	+= 88pm860x.o
>  obj-$(CONFIG_MFD_88PM800)	+= 88pm800.o 88pm80x.o
>  obj-$(CONFIG_MFD_88PM805)	+= 88pm805.o 88pm80x.o
>  obj-$(CONFIG_MFD_88PM886_PMIC)	+= 88pm886.o
> +obj-$(CONFIG_MFD_AAEON_MCU)	+= aaeon-mcu.o
>  obj-$(CONFIG_MFD_ACT8945A)	+= act8945a.o
>  obj-$(CONFIG_MFD_SM501)		+= sm501.o
>  obj-$(CONFIG_ARCH_BCM2835)	+= bcm2835-pm.o
> diff --git a/drivers/mfd/aaeon-mcu.c b/drivers/mfd/aaeon-mcu.c
> new file mode 100644
> index 000000000000..3b4e2d891534
> --- /dev/null
> +++ b/drivers/mfd/aaeon-mcu.c
> @@ -0,0 +1,204 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Aaeon MCU driver
> + *
> + * Copyright (C) 2026 Bootlin
> + * Author: Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
> + * Author: Thomas Perrot <thomas.perrot@bootlin.com>
> + */
> +
> +#include <linux/err.h>
> +#include <linux/i2c.h>
> +#include <linux/mfd/aaeon-mcu.h>
> +#include <linux/mfd/core.h>
> +#include <linux/platform_device.h>
> +#include <linux/regmap.h>
> +#include <linux/slab.h>
> +
> +struct aaeon_mcu {
> +	struct i2c_client *client;
> +	u8 *cmd;      /* DMA-safe 3-byte write buffer [opcode, arg, value] */
> +	u8 *response; /* DMA-safe 1-byte read buffer for MCU acknowledgment */
> +};
> +
> +static const struct mfd_cell aaeon_mcu_devs[] = {
> +	MFD_CELL_BASIC("aaeon-mcu-wdt", NULL, NULL, 0, 0),
> +	MFD_CELL_BASIC("aaeon-mcu-gpio", NULL, NULL, 0, 0),
> +};
> +
> +/* Number of bytes in a MCU command: [opcode, arg, value] */
> +#define AAEON_MCU_CMD_LEN      3
> +
> +/*
> + * Custom regmap bus for the Aaeon MCU I2C protocol.
> + *
> + * The MCU uses a fixed 3-byte command format [opcode, arg, value] followed
> + * by a 1-byte response. It requires a STOP condition between the command
> + * write and the response read, so two separate i2c_transfer() calls are
> + * issued.  The regmap lock serialises concurrent accesses from the GPIO
> + * and watchdog child drivers.
> + *
> + * Register addresses are encoded as a 16-bit big-endian value where the
> + * high byte is the opcode and the low byte is the argument, matching the
> + * wire layout produced by regmap for reg_bits=16.
> + */
> +
> +static int aaeon_mcu_regmap_write(void *context, const void *data, size_t count)
> +{
> +	struct aaeon_mcu *mcu = context;
> +	struct i2c_client *client = mcu->client;
> +	struct i2c_msg write_msg;
> +	/* The MCU always sends a response byte after each command; discard it. */
> +	struct i2c_msg response_msg;
> +	int ret;
> +
> +	memcpy(mcu->cmd, data, count);
> +
> +	write_msg.addr  = client->addr;
> +	write_msg.flags = 0;
> +	write_msg.buf   = mcu->cmd;
> +	write_msg.len   = count;
> +
> +	response_msg.addr  = client->addr;
> +	response_msg.flags = I2C_M_RD;
> +	response_msg.buf   = mcu->response;
> +	response_msg.len   = 1;
> +
> +	ret = i2c_transfer(client->adapter, &write_msg, 1);
> +	if (ret < 0)
> +		return ret;
> +	if (ret != 1)
> +		return -EIO;
> +
> +	ret = i2c_transfer(client->adapter, &response_msg, 1);
> +	if (ret < 0)
> +		return ret;
> +	if (ret != 1)
> +		return -EIO;
> +
> +	return 0;
> +}
> +
> +static int aaeon_mcu_regmap_read(void *context, const void *reg_buf,
> +				 size_t reg_size, void *val_buf, size_t val_size)
> +{
> +	struct aaeon_mcu *mcu = context;
> +	struct i2c_client *client = mcu->client;
> +	struct i2c_msg write_msg;
> +	struct i2c_msg read_msg;
> +	int ret;
> +
> +	/*
> +	 * reg_buf holds the 2-byte big-endian register address [opcode, arg].
> +	 * Append a trailing 0x00 to form the full 3-byte MCU command.
> +	 */
> +	mcu->cmd[0] = ((u8 *)reg_buf)[0];
> +	mcu->cmd[1] = ((u8 *)reg_buf)[1];
> +	mcu->cmd[2] = 0x00;
> +
> +	write_msg.addr  = client->addr;
> +	write_msg.flags = 0;
> +	write_msg.buf   = mcu->cmd;
> +	write_msg.len   = AAEON_MCU_CMD_LEN;
> +
> +	read_msg.addr  = client->addr;
> +	read_msg.flags = I2C_M_RD;
> +	read_msg.buf   = val_buf;
> +	read_msg.len   = val_size;
> +
> +	ret = i2c_transfer(client->adapter, &write_msg, 1);
> +	if (ret < 0)
> +		return ret;
> +	if (ret != 1)
> +		return -EIO;
> +
> +	ret = i2c_transfer(client->adapter, &read_msg, 1);
> +	if (ret < 0)
> +		return ret;
> +	if (ret != 1)
> +		return -EIO;
> +
> +	return 0;
> +}
> +
> +static const struct regmap_bus aaeon_mcu_regmap_bus = {
> +	.write = aaeon_mcu_regmap_write,
> +	.read  = aaeon_mcu_regmap_read,
> +};
> +
> +static bool aaeon_mcu_volatile_reg(struct device *dev, unsigned int reg)
> +{
> +	/*
> +	 * GPIO input registers are driven by external signals and can change
> +	 * at any time without CPU involvement, always read from hardware.
> +	 *
> +	 * The watchdog status register reflects hardware state and can change
> +	 * autonomously.
> +	 *
> +	 * All other registers are written by the driver and their values are
> +	 * stable, so they can be safely cached.
> +	 */
> +	if ((reg >> 8) == AAEON_MCU_READ_GPIO_OPCODE)
> +		return true;
> +	if (reg == AAEON_MCU_REG(AAEON_MCU_CONTROL_WDT_OPCODE, 0x02))
> +		return true;
> +	return false;
> +}
> +
> +static const struct regmap_config aaeon_mcu_regmap_config = {
> +	.reg_bits          = 16,
> +	.val_bits          = 8,
> +	.reg_format_endian = REGMAP_ENDIAN_BIG,
> +	.max_register      = AAEON_MCU_MAX_REGISTER,
> +	.volatile_reg      = aaeon_mcu_volatile_reg,
> +	.cache_type        = REGCACHE_MAPLE,
> +};
> +
> +static int aaeon_mcu_probe(struct i2c_client *client)
> +{
> +	struct aaeon_mcu *mcu;

Nit: We usually call this ddata, but it's not a blocker.

> +	struct regmap *regmap;
> +
> +	mcu = devm_kzalloc(&client->dev, sizeof(*mcu), GFP_KERNEL);
> +	if (!mcu)
> +		return -ENOMEM;
> +
> +	mcu->client = client;
> +
> +	mcu->cmd = devm_kzalloc(&client->dev, AAEON_MCU_CMD_LEN * sizeof(*mcu->cmd), GFP_KERNEL);
> +	if (!mcu->cmd)
> +		return -ENOMEM;
> +
> +	mcu->response = devm_kzalloc(&client->dev, sizeof(*mcu->response), GFP_KERNEL);
> +	if (!mcu->response)
> +		return -ENOMEM;
> +
> +	regmap = devm_regmap_init(&client->dev, &aaeon_mcu_regmap_bus,
> +				  mcu, &aaeon_mcu_regmap_config);
> +	if (IS_ERR(regmap))
> +		return dev_err_probe(&client->dev, PTR_ERR(regmap),
> +				     "failed to initialize regmap\n");
> +
> +	return devm_mfd_add_devices(&client->dev, PLATFORM_DEVID_AUTO,
> +				    aaeon_mcu_devs, ARRAY_SIZE(aaeon_mcu_devs),
> +				    NULL, 0, NULL);
> +}
> +
> +static const struct of_device_id aaeon_mcu_of_match[] = {
> +	{ .compatible = "aaeon,srg-imx8p-mcu" },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, aaeon_mcu_of_match);
> +
> +static struct i2c_driver aaeon_mcu_driver = {
> +	.driver = {
> +		.name = "aaeon_mcu",

Nit: This should be a '-'.

> +		.of_match_table = aaeon_mcu_of_match,
> +	},
> +	.probe = aaeon_mcu_probe,
> +};
> +module_i2c_driver(aaeon_mcu_driver);
> +
> +MODULE_DESCRIPTION("Aaeon MCU Driver");
> +MODULE_AUTHOR("Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>");
> +MODULE_LICENSE("GPL");
> diff --git a/include/linux/mfd/aaeon-mcu.h b/include/linux/mfd/aaeon-mcu.h
> new file mode 100644
> index 000000000000..3a1aeec85d60
> --- /dev/null
> +++ b/include/linux/mfd/aaeon-mcu.h
> @@ -0,0 +1,40 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +/*
> + * Aaeon MCU driver definitions
> + *
> + * Copyright (C) 2026 Bootlin
> + * Author: Jérémie Dautheribes <jeremie.dautheribes@bootlin.com>
> + * Author: Thomas Perrot <thomas.perrot@bootlin.com>
> + */
> +
> +#ifndef __LINUX_MFD_AAEON_MCU_H
> +#define __LINUX_MFD_AAEON_MCU_H
> +
> +/*
> + * MCU register address: the high byte is the command opcode, the low
> + * byte is the argument.  This matches the 3-byte wire format
> + * [opcode, arg, value] used by the MCU I2C protocol.
> + */
> +#define AAEON_MCU_REG(op, arg)		(((op) << 8) | (arg))
> +
> +/*
> + * Opcode for GPIO input reads. These registers are volatile, their values
> + * are driven by external signals and can change without CPU involvement.
> + * Used by the MFD driver's volatile_reg callback to bypass the regmap cache.
> + */
> +#define AAEON_MCU_READ_GPIO_OPCODE	0x72
> +
> +/*
> + * Opcode for watchdog control and status commands.
> + * The status register (arg=0x02) reflects hardware state and is volatile.
> + */
> +#define AAEON_MCU_CONTROL_WDT_OPCODE	0x63
> +
> +/*
> + * Highest register address in the MCU register map.
> + * The WRITE_GPIO opcode (0x77) with the highest GPIO argument (0x0B = 11,
> + * i.e. MAX_GPIOS - 1) produces the largest encoded address.
> + */
> +#define AAEON_MCU_MAX_REGISTER		AAEON_MCU_REG(0x77, 0x0B)
> +
> +#endif /* __LINUX_MFD_AAEON_MCU_H */
> 
> -- 
> 2.53.0
> 

-- 
Lee Jones