[PATCH v2 1/3] media: open.rst: better document device node naming

[Mauro Carvalho Chehab]

Right now, only kAPI documentation describes the device naming.
However, such description is needed at the uAPI too. Add it,
and describe how to get an unique identify for a given device.

Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>
---
 Documentation/media/uapi/v4l/open.rst | 40 ++++++++++++++++++++++++++++++-----
 1 file changed, 35 insertions(+), 5 deletions(-)

diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index afd116edb40d..9b98d10d5153 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -7,12 +7,12 @@ Opening and Closing Devices
 ***************************
 
 
-Device Naming
-=============
+V4L2 Device Node Naming
+=======================
 
 V4L2 drivers are implemented as kernel modules, loaded manually by the
 system administrator or automatically when a device is first discovered.
-The driver modules plug into the "videodev" kernel module. It provides
+The driver modules plug into the ``videodev`` kernel module. It provides
 helper functions and a common application interface specified in this
 document.
 
@@ -20,8 +20,38 @@ Each driver thus loaded registers one or more device nodes with major
 number 81 and a minor number between 0 and 255. Minor numbers are
 allocated dynamically unless the kernel is compiled with the kernel
 option CONFIG_VIDEO_FIXED_MINOR_RANGES. In that case minor numbers
-are allocated in ranges depending on the device node type (video, radio,
-etc.).
+are allocated in ranges depending on the device node type.
+
+The existing V4L2 device node types are:
+
+======================== ======================================================
+Default device node name Usage
+======================== ======================================================
+``/dev/videoX``		 Video input/output devices
+``/dev/vbiX``		 Vertical blank data (i.e. closed captions, teletext)
+``/dev/radioX``		 Radio tuners
+``/dev/swradioX``	 Software Defined Radio tuners
+``/dev/v4l-touchX``	 Touch sensors
+======================== ======================================================
+
+Where ``X`` is a non-negative number.
+
+.. note::
+
+   1. The actual device node name is system-dependent, as udev rules may apply.
+   2. There's not warranty that ``X`` will remain the same for the same
+      device, as the number depends on the device driver's probe order.
+      If you need an unique name, udev default rules produce
+      ``/dev/v4l/by-id/`` and ``/dev/v4l/by-path/`` that can use to uniquelly
+      identify a V4L2 device node::
+
+	$ tree /dev/v4l
+	/dev/v4l
+	âââ by-id
+	â âââ usb-OmniVision._USB_Camera-B4.04.27.1-video-index0 -> ../../video0
+	âââ by-path
+	    âââ pci-0000:00:14.0-usb-0:2:1.0-video-index0 -> ../../video0
+
 
 Many drivers support "video_nr", "radio_nr" or "vbi_nr" module
 options to select specific video/radio/vbi node numbers. This allows the
-- 
2.13.3