From 176fb0d108f7495ccf9aa127e1342a1a0d87e004 Mon Sep 17 00:00:00 2001 From: Laurent Pinchart Date: Wed, 9 Dec 2009 08:39:58 -0300 Subject: [media] media: Media device The media_device structure abstracts functions common to all kind of media devices (v4l2, dvb, alsa, ...). It manages media entities and offers a userspace API to discover and configure the media device internal topology. Signed-off-by: Laurent Pinchart Acked-by: Hans Verkuil Signed-off-by: Mauro Carvalho Chehab --- Documentation/media-framework.txt | 67 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+) create mode 100644 Documentation/media-framework.txt (limited to 'Documentation/media-framework.txt') diff --git a/Documentation/media-framework.txt b/Documentation/media-framework.txt new file mode 100644 index 00000000000..1844c3f1072 --- /dev/null +++ b/Documentation/media-framework.txt @@ -0,0 +1,67 @@ +Linux kernel media framework +============================ + +This document describes the Linux kernel media framework, its data structures, +functions and their usage. + + +Introduction +------------ + +The media controller API is documented in DocBook format in +Documentation/DocBook/v4l/media-controller.xml. This document will focus on +the kernel-side implementation of the media framework. + + +Media device +------------ + +A media device is represented by a struct media_device instance, defined in +include/media/media-device.h. Allocation of the structure is handled by the +media device driver, usually by embedding the media_device instance in a +larger driver-specific structure. + +Drivers register media device instances by calling + + media_device_register(struct media_device *mdev); + +The caller is responsible for initializing the media_device structure before +registration. The following fields must be set: + + - dev must point to the parent device (usually a pci_dev, usb_interface or + platform_device instance). + + - model must be filled with the device model name as a NUL-terminated UTF-8 + string. The device/model revision must not be stored in this field. + +The following fields are optional: + + - serial is a unique serial number stored as a NUL-terminated ASCII string. + The field is big enough to store a GUID in text form. If the hardware + doesn't provide a unique serial number this field must be left empty. + + - bus_info represents the location of the device in the system as a + NUL-terminated ASCII string. For PCI/PCIe devices bus_info must be set to + "PCI:" (or "PCIe:") followed by the value of pci_name(). For USB devices, + the usb_make_path() function must be used. This field is used by + applications to distinguish between otherwise identical devices that don't + provide a serial number. + + - hw_revision is the hardware device revision in a driver-specific format. + When possible the revision should be formatted with the KERNEL_VERSION + macro. + + - driver_version is formatted with the KERNEL_VERSION macro. The version + minor must be incremented when new features are added to the userspace API + without breaking binary compatibility. The version major must be + incremented when binary compatibility is broken. + +Upon successful registration a character device named media[0-9]+ is created. +The device major and minor numbers are dynamic. The model name is exported as +a sysfs attribute. + +Drivers unregister media device instances by calling + + media_device_unregister(struct media_device *mdev); + +Unregistering a media device that hasn't been registered is *NOT* safe. -- cgit v1.2.3