Hi Niklas, On Mon, Apr 24, 2023 at 09:20:22PM +0200, Niklas Söderlund wrote: > Hi Sakari, > > On 2023-04-14 14:07:40 +0300, Sakari Ailus wrote: > > Hi Jacopo, > > > > On Thu, Apr 13, 2023 at 06:50:04PM +0200, Jacopo Mondi wrote: > > > Hi Sakari > > > > > > On Thu, Mar 30, 2023 at 02:58:38PM +0300, Sakari Ailus wrote: > > > > V4L2 async sub-device matching originally used the device nodes only. > > > > Endpoint nodes were taken into use instead as using the device nodes was > > > > problematic for it was in some cases ambiguous which link might have been > > > > in question. > > > > > > > > There is however no need to use endpoint nodes on both sides, as the async > > > > sub-device's fwnode can always be trivially obtained using > > > > fwnode_graph_get_remote_endpoint() when needed while what counts is > > > > whether or not the link is between two device nodes, i.e. the device nodes > > > > match. > > > > > > > > > > As you know I'm a bit debated. > > > > > > Strict endpoint-matching requires one subdev to be registed per each > > > endpoint, and this is tedious for drivers that have to register a > > > subdev for each of its endpoints > > > > > > Allowing a subdev to be matched multiple times on different endpoints > > > gives a way for lazy drivers to take a shortcut and simplify their > > > topologies to a single subdev, when they would actually need more. > > > > I'd say this is really about interface design, not being "lazy". It depends > > on the sub-device. Ideally the framework should be also as easy for drivers > > drivers to use as possible. > > > > What is not supported, though, is multiple sub-devices with a single device > > node. Do we need that? At least I don't think I came across a driver that > > would. > > If I understand you correctly about multiple sub-device from a single > device node, this exists today. The ADV748x driver have a single device > node in DT and register multiple sub-devices, one for each source > endpoint. > > The ADV748x have two CSI-2 transmitters, one 4-lane and one 1-lane as > well as two different video capture "ports" one HDMI and one CVBS. Both > capture ports can be active at the same time and routed internally > inside the ADV748x to the two different CSI-2 transmitters. > > In order todo this the ADV748x register multiple subdevices and modifies > the fwnode to be the endpoint instead of the device node. So the change > in this patch for ADV748x driver would break that driver. Ah, indeed. I guess I'll need to support that case as well then. It doesn't seem to be troublesome to implement, but I'm tempted making it a special case: every other driver would apparently be fine matching with device fwnode whereas doing endpoint-to-endpoint matching adds complexity to the drivers. This patch removes about 100 lines of rather ugly code largely from v4l2-async. There are other issues in the set with connection-subdev relations, I'll post v2 to address those as well. -- Kind regards, Sakari Ailus
