Hi folks, Here are the meeting notes on the IRC meeting that took place 11th and 13th last October. The brief summary is below, the full log can be found here:
<URL:http://www.retiisi.org.uk/v4l2/notes/v4l2-naming-2017-10-11.txt> Attendees: Laurent Pinchart Mauro Chehab Hans Verkuil Lars-Peter Clausen Sylwester Nawrocki Sakari Ailus Notes: - It was decided to call a group of multiple interconnected hardware devices that that are designed to operate together as a "media hardware complex". We haven't had a proper term for this in the past. Effectively this means device that can be accessed through a given media device. - "Device", when it refers to a device node on a file system, shall be replaced by "device node" in uAPI documentation if there's any ambiguity. The same applies to "device" when it refers to hardware, i.e. "hardware device". Further use of the "device" to refer either is fine as long as there is no ambiguity of what it means. - During the discussion on V4L2 sub-devices as V4L2 devices, the following points were brought up: - V4L2 sub-device nodes are V4L2 device nodes in the following respects: - They share the same major number as V4L2 and they are implemented by the V4L2 framework (as instantiated by drivers). - V4L2 sub-devices share some IOCTLs such as V4L2 controls with other V4L2 device nodes. - They do share the "V4L2" in their name. - But there are some differences as well: - V4L2 sub-devices implement only a handful of IOCTLs, most of which are uniformly implemented by all other V4L2 device node types (video, radio, touch). E.g. QUERYCAP is not implemented for sub-devices albeit there have been proposals to add this for unrelated reasons. - Historically V4L2 sub-device documentation has been always outside the main V4L2 documentation (section 1 in particular). This is primarily a documentation issue though. - Some V4L2 sub-device IOCTLs have different arguments from the V4L2 IOCTLs due to e.g. the fact that sub-devices are a control only interface dealing with media bus formats whereas V4L2 video device nodes deal with in-memory V4L2 formats. - Documentation-wise, there's a common need to refer to V4L2 device nodes which are not sub-device nodes as the rest have quite a bit in common. In this case, they should be called "V4L2 video device node" or "V4L2 radio device node", or "V4L2 video/radio device nodes". This technically does not include touch device nodes. - This distinction enables calling also V4L2 sub-device nodes as V4L2 device nodes, which was also agreed. The corresponding changes should be made to the uAPI documentation. Let me know if there are inaccuracies or if you feel something is missing. It's been a while we had the meeting but this is why IRC meetings are great: you can write the meeting notes afterwards with pretty good accuracy. :-) Also thanks to Mauro for reminding me we had no proper notes on the meeting. -- Kind regards, Sakari Ailus e-mail: sakari.ai...@iki.fi
