drivers/usbdev: add UVC gadget class driver

Add USB Video Class 1.1 gadget driver supporting Bulk transport
with uncompressed YUY2 video streaming. Resolution and frame
interval are negotiated dynamically via PROBE/COMMIT control.

- uvc.h: protocol constants, streaming control struct, public API
- uvc.c: class driver with PROBE/COMMIT, bulk EP, /dev/uvc0 chardev
- Kconfig/Make.defs: USBUVC config and build rules
- boardctl.c: BOARDIOC_USBDEV_UVC standalone init path

Hardened against host disconnect:
- Removed nxmutex_lock from USB interrupt context paths
- Added 30s semaphore timeout in uvc_write with EP_CANCEL fallback
- Drain stale wrsem counts in VS_COMMIT before new stream
- Guard uvc_streaming_stop() against double EP_CANCEL race
- Handle EP_SUBMIT returning -ESHUTDOWN gracefully

Signed-off-by: wangjianyu3 <wangjianyu3@xiaomi.com>

Documentation/components/drivers/special/index.rst

@@ -44,6 +44,7 @@ following section.
   syslog.rst
   sdio.rst
   usbdev.rst
+  uvc.rst
   usbhost.rst
   usbmisc.rst
   usbmonitor.rst

Documentation/components/drivers/special/uvc.rst

@@ -0,0 +1,127 @@
+======================================
+USB Video Class (UVC) Gadget Driver
+======================================
+
+Overview
+========
+
+The UVC gadget driver (``drivers/usbdev/uvc.c``) implements a USB Video Class
+1.1 device that makes NuttX appear as a USB webcam to the host.  The driver
+exposes a character device (``/dev/uvc0``) that applications write video frames
+to.  It handles all UVC class-specific control requests (PROBE / COMMIT)
+internally and uses bulk transfers for video data.
+
+The driver supports two modes:
+
+- **Standalone** – the UVC function is the only USB class on the bus.
+- **Composite** – the UVC function is combined with other USB class drivers
+  (e.g. CDC/ACM) via the NuttX composite device framework.
+
+Features
+========
+
+- UVC 1.1 compliant (uncompressed YUY2 format)
+- Bulk transfer mode for video data
+- Automatic PROBE / COMMIT negotiation with the host
+- ``poll()`` support – applications can wait for the host to start streaming
+  (``POLLOUT``) and detect disconnection (``POLLHUP``)
+- Runtime video parameters – resolution and frame rate are passed at
+  initialization time, so USB descriptors always match the actual sensor
+- ``boardctl()`` integration for easy application-level bring-up
+
+Configuration
+=============
+
+The driver is enabled through the following Kconfig options:
+
+.. code-block:: kconfig
+
+   CONFIG_USBUVC=y                  # Enable UVC gadget support
+   CONFIG_USBUVC_COMPOSITE=n        # Set y for composite device mode
+   CONFIG_USBUVC_EPBULKIN=1         # Bulk IN endpoint number (standalone)
+   CONFIG_USBUVC_EP0MAXPACKET=64    # EP0 max packet size (standalone)
+   CONFIG_USBUVC_EPBULKIN_FSSIZE=64 # Bulk IN full-speed max packet size
+   CONFIG_USBUVC_NWRREQS=4          # Number of pre-allocated write requests
+   CONFIG_USBUVC_NPOLLWAITERS=2     # Number of poll waiters
+
+Header Files
+============
+
+- ``include/nuttx/usb/uvc.h`` – Public API, UVC descriptor constants, and
+  data structures.
+
+Data Structures
+===============
+
+``struct uvc_params_s``
+-----------------------
+
+Passed to the initialization function so that USB descriptors reflect the
+actual sensor capabilities::
+
+  struct uvc_params_s
+  {
+    uint16_t width;    /* Frame width in pixels  */
+    uint16_t height;   /* Frame height in pixels */
+    uint8_t  fps;      /* Frames per second      */
+  };
+
+Public Interfaces
+=================
+
+Standalone Mode
+---------------
+
+``usbdev_uvc_initialize()``
+  Initialize the UVC gadget and register ``/dev/uvc0``.  *params* may be
+  ``NULL`` to use defaults (320 × 240 @ 5 fps).  Returns a handle for later
+  ``usbdev_uvc_uninitialize()``.
+
+``usbdev_uvc_uninitialize()``
+  Tear down the UVC gadget and unregister the character device.
+
+Composite Mode
+--------------
+
+``usbdev_uvc_classobject()``
+  Create a UVC class driver instance for use inside a composite device.
+
+``usbdev_uvc_classuninitialize()``
+  Destroy a class driver instance created by ``usbdev_uvc_classobject()``.
+
+``usbdev_uvc_get_composite_devdesc()``
+  Fill a ``composite_devdesc_s`` for the composite framework.
+
+boardctl Integration
+--------------------
+
+Applications can manage the UVC gadget through ``boardctl()``::
+
+  struct boardioc_usbdev_ctrl_s ctrl;
+  struct uvc_params_s params = { .width = 320, .height = 240, .fps = 15 };
+  FAR void *handle = (FAR void *)&params;
+
+  ctrl.usbdev   = BOARDIOC_USBDEV_UVC;
+  ctrl.action   = BOARDIOC_USBDEV_CONNECT;
+  ctrl.instance = 0;
+  ctrl.config   = 0;
+  ctrl.handle   = &handle;
+
+  boardctl(BOARDIOC_USBDEV_CONTROL, (uintptr_t)&ctrl);
+
+  /* ... use /dev/uvc0 ... */
+
+  ctrl.action = BOARDIOC_USBDEV_DISCONNECT;
+  boardctl(BOARDIOC_USBDEV_CONTROL, (uintptr_t)&ctrl);
+
+Device Operation
+================
+
+1. The application opens ``/dev/uvc0`` for writing.
+2. Use ``poll()`` with ``POLLOUT`` to wait for the USB host to start streaming
+   (i.e. the host sends a VS_COMMIT_CONTROL SET_CUR request).
+3. Write complete video frames via ``write()``.  The driver prepends a 2-byte
+   UVC payload header (with FID / EOF bits) automatically.
+4. When the host stops streaming, ``write()`` returns ``-EAGAIN``.  The
+   application can ``poll()`` again to wait for the host to restart.
+5. ``POLLHUP`` is reported when the host explicitly stops streaming.