From: Mauro Carvalho Chehab <mchehab@s-opensource.com>
To: Linux Doc Mailing List <linux-doc@vger.kernel.org>,
Linux Media Mailing List <linux-media@vger.kernel.org>
Cc: Mauro Carvalho Chehab <mchehab@s-opensource.com>,
Mauro Carvalho Chehab <mchehab@infradead.org>,
linux-kernel@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>
Subject: [PATCH v3 2/7] media: open.rst: better document device node naming
Date: Fri, 25 Aug 2017 12:11:52 -0300 [thread overview]
Message-ID: <154729518e406bac4fdd53ce22e027936ece7b35.1503673702.git.mchehab@s-opensource.com> (raw)
In-Reply-To: <cover.1503673702.git.mchehab@s-opensource.com>
In-Reply-To: <cover.1503673702.git.mchehab@s-opensource.com>
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@s-opensource.com>
---
Documentation/media/uapi/v4l/open.rst | 39 ++++++++++++++++++++++++++++++++---
1 file changed, 36 insertions(+), 3 deletions(-)
diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst
index afd116edb40d..e7160f667499 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -7,12 +7,14 @@ Opening and Closing Devices
***************************
-Device Naming
-=============
+.. _v4l2_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.
@@ -23,6 +25,37 @@ option CONFIG_VIDEO_FIXED_MINOR_RANGES. In that case minor numbers
are allocated in ranges depending on the device node type (video, radio,
etc.).
+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 be used to
+ uniquely identify a V4L2 device node::
+
+ $ tree /dev/v4l
+ /dev/v4l
+ ├── by-id
+ │ └── usb-OmniVision._USB_Camera-B4.04.27.1-video-index0 -> ../../video0
+ └── by-path
+ └── 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
user to request that the device node is named e.g. /dev/video5 instead
--
2.13.3
next prev parent reply other threads:[~2017-08-25 15:13 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-25 15:11 [PATCH v3 0/7] document types of hardware control for V4L2 Mauro Carvalho Chehab
2017-08-25 15:11 ` [PATCH v3 1/7] media: add glossary.rst with a glossary of terms used at V4L2 spec Mauro Carvalho Chehab
2017-08-25 15:11 ` Mauro Carvalho Chehab [this message]
2017-08-25 15:11 ` [PATCH v3 3/7] media: open.rst: remove the minor number range Mauro Carvalho Chehab
2017-08-25 15:11 ` [PATCH v3 4/7] media: open.rst: document devnode-centric and mc-centric types Mauro Carvalho Chehab
2017-08-25 15:11 ` [PATCH v3 5/7] media: open.rst: Adjust some terms to match the glossary Mauro Carvalho Chehab
2017-08-25 15:11 ` [PATCH v3 6/7] media: videodev2: add a flag for MC-centric devices Mauro Carvalho Chehab
2017-08-25 15:11 ` [PATCH v3 7/7] media: open.rst: add a notice about subdev-API on vdev-centric Mauro Carvalho Chehab
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