From c31b87ee1e0e208f046155bbd7b27ac4be5feb66 Mon Sep 17 00:00:00 2001
From: raiden00pl <raiden00@railab.me>
Date: Wed, 23 Sep 2026 11:58:19 +0200
Subject: [PATCH] drivers/ioexpander: add an optional pin PWM operation

Add an ioe_setpwm operation (guarded by CONFIG_IOEXPANDER_PWM) for
expanders that can modulate their outputs, e.g. through a LED driver
engine.

Assisted-by: Claude Code
Signed-off-by: raiden00pl <raiden00@railab.me>
---
 .../components/drivers/special/ioexpander.rst | 12 +++++++++
 drivers/ioexpander/Kconfig                    |  8 ++++++
 include/nuttx/ioexpander/ioexpander.h         | 26 +++++++++++++++++++
 3 files changed, 46 insertions(+)

diff --git a/Documentation/components/drivers/special/ioexpander.rst b/Documentation/components/drivers/special/ioexpander.rst
index 5a4e19af896..8b1a1d9a5ef 100644
--- a/Documentation/components/drivers/special/ioexpander.rst
+++ b/Documentation/components/drivers/special/ioexpander.rst
@@ -273,6 +273,18 @@ driver operations table (``struct ioexpander_ops_s``):
    - ``IOEXP_READBUF`` reads the buffered/register value cached by the
      expander.
 
+Pin PWM control
+---------------
+
+``CONFIG_IOEXPANDER_PWM`` enables the optional ``ioe_setpwm`` operation.
+
+.. c:macro:: IOEXP_SETPWM(dev, pin, duty)
+
+   Set a physical pin's duty cycle: ``duty`` is a ``uint16_t`` value from
+   ``0`` (off) to ``0xffff`` (fully on). Returns 0 on success or a negative
+   errno on failure. The caller must ensure ``dev->ops->ioe_setpwm`` is
+   non-NULL; the macro does not check it. Frequency control is not provided.
+
 Multi-pin operations
 --------------------
 
diff --git a/drivers/ioexpander/Kconfig b/drivers/ioexpander/Kconfig
index a0ff52ec85b..3f6cac94970 100644
--- a/drivers/ioexpander/Kconfig
+++ b/drivers/ioexpander/Kconfig
@@ -618,6 +618,14 @@ config IOEXPANDER_MULTIPIN
 		This settings enable the definition of routines for
 		optimized simultaneous access to multiple pins.
 
+config IOEXPANDER_PWM
+	bool "Support pin PWM control"
+	default n
+	---help---
+		This setting enables an operation to control the PWM duty cycle
+		of I/O expander pins, for expanders that can modulate their
+		outputs (e.g. through a LED driver engine).
+
 endif # IOEXPANDER
 
 config DEV_GPIO
diff --git a/include/nuttx/ioexpander/ioexpander.h b/include/nuttx/ioexpander/ioexpander.h
index 218bd3c34a6..f9fba627495 100644
--- a/include/nuttx/ioexpander/ioexpander.h
+++ b/include/nuttx/ioexpander/ioexpander.h
@@ -253,6 +253,28 @@
 
 #endif /* CONFIG_IOEXPANDER_MULTIPIN */
 
+#ifdef CONFIG_IOEXPANDER_PWM
+
+/****************************************************************************
+ * Name: IOEXP_SETPWM
+ *
+ * Description:
+ *   Set the pin PWM duty cycle. Optional.
+ *
+ * Input Parameters:
+ *   dev  - Device-specific state data
+ *   pin  - The index of the pin to alter in this call
+ *   duty - The duty cycle, where 0 is off and 0xffff is fully on
+ *
+ * Returned Value:
+ *   0 on success, else a negative error code
+ *
+ ****************************************************************************/
+
+#define IOEXP_SETPWM(dev,pin,duty) ((dev)->ops->ioe_setpwm(dev,pin,duty))
+
+#endif /* CONFIG_IOEXPANDER_PWM */
+
 /****************************************************************************
  * Name: IOEP_ATTACH
  *
@@ -358,6 +380,10 @@ struct ioexpander_ops_s
                                ioe_callback_t callback, FAR void *arg);
   CODE int (*ioe_detach)(FAR struct ioexpander_dev_s *dev, FAR void *handle);
 #endif
+#ifdef CONFIG_IOEXPANDER_PWM
+  CODE int (*ioe_setpwm)(FAR struct ioexpander_dev_s *dev, uint8_t pin,
+                         uint16_t duty);
+#endif
 };
 
 struct ioexpander_dev_s