On 03/19/2018 01:00 PM, Pavel Machek wrote: > Hi! > >>> Pavel, >>> >>> I appreciate your efforts of adding support for mc-based devices to >>> libv4l. > > Thanks. > >>> I guess the main poin that Hans is pointing is that we should take >>> extra care in order to avoid adding new symbols to libv4l ABI/API >>> without being sure that they'll be needed in long term, as removing >>> or changing the API is painful for app developers, and keeping it >>> ABI compatible with apps compiled against previous versions of the >>> library is very painful for us. >> >> Indeed. Sorry if I wasn't clear on that. > > Aha, ok, no, I did not get that. > >>> The hole idea is that generic applications shouldn't notice >>> if the device is using a mc-based device or not. >> >> What is needed IMHO is an RFC that explains how you want to solve this >> problem, what the parser would look like, how this would configure a >> complex pipeline for use with libv4l-using applications, etc. >> >> I.e., a full design. >> >> And once everyone agrees that that design is solid, then it needs to be >> implemented. >> >> I really want to work with you on this, but I am not looking for partial >> solutions. > > Well, expecting design to be done for opensource development is a bit > unusual :-). Why? We have done that quite often in the past. Media is complex and you need to decide on a design up front. > I really see two separate tasks > > 1) support for configuring pipeline. I believe this is best done out > of libv4l2. It outputs description file, format below. Currently I > have implemented this is in Python. File format is below. You do need this, but why outside of libv4l2? I'm not saying I disagree with you, but you need to give reasons for that. > 2) support for running libv4l2 on mc-based devices. I'd like to do > that. > > Description file would look like. (# comments would not be not part of file). > > V4L2MEDIADESC > 3 # number of files to open > /dev/video2 > /dev/video6 > /dev/video3 This won't work. The video nodes numbers (or even names) can change. Instead these should be entity names from the media controller. > 3 # number of controls to map. Controls not mentioned here go to > # device 0 automatically. Sorted by control id. > # Device 0 > 00980913 1 > 009a0003 1 > 009a000a 2 You really don't need to specify the files to open. All you need is to specify the entity ID and the list of controls that you need. Then libv4l can just figure out which device node(s) to open for that. > > We can parse that easily without requiring external libraries. Sorted > data allow us to do binary search. But none of this addresses setting up the initial video pipeline or changing formats. We probably want to support that as well. For that matter: what is it exactly that we want to support? I.e. where do we draw the line? A good test platform for this (outside the N900) is the i.MX6 platform. Regards, Hans
