Hi Luca, On Fri, Mar 22, 2019 at 05:52:15PM +0100, Luca Ceresoli wrote: > Hi, > > thanks for the follow-up. > > On 20/03/19 18:14, Jacopo Mondi wrote: > >>>> This is probably the wrong patch to use an example, as this one is for > >>>> a multiplexed interface, where there is no need to go through an > >>>> s_stream() for the two CSI-2 endpoints, but as you pointed out in our > >>>> brief offline chat, the AFE->TX routing example for this very device > >>>> is a good one: if we change the analogue source that is internally > >>>> routed to the CSI-2 output of the adv748x, do we need to s_stream(1) > >>>> the now routed entity and s_stream(0) on the not not-anymore-routed > >>>> one? > >>>> > >>>> My gut feeling is that this is up to userspace, as it should know > >>>> what are the requirements of the devices in the system, but this mean > >>>> going through an s_stream(0)/s_stream(1) sequence on the video device, > >>>> and that would interrupt the streaming for sure. > >>>> > >>>> At the same time, I don't feel too much at ease with the idea of > >>>> s_routing calling s_stream on the entity' remote subdevices, as this > >>>> would skip the link format validation that media_pipeline_start() > >>>> performs. > >>> > >>> The link validation must be done in this case as well, it may not be > >>> simply skipped. > >> > >> Agreed. > >> > >> The routing VS pipeline validation point is a very important one. The > >> current proposed workflow is: > >> > >> 1. the pipeline is validated as a whole, having knowledge of all the > >> entities > > > > let me specify this to avoid confusions: > > "all the entities -with an active route in the pipeline-" > > > >> 2. streaming is started > >> 3. s_routing is called on an entity (not on the pipeline!) > >> > >> Now the s_routing function in the entity driver is not in a good > >> position to validate the candidate future pipeline as a whole. > >> > >> Naively I'd say there are two possible solutions: > >> > >> 1. the s_routing reaches the pipeline first, then the new pipeline is > >> computed and verified, and if verification succeeds it is applied > >> 2. a partial pipeline verification mechanism is added, so the entity > >> receiving a s_routing request to e.g. change the sink pad can invoke > >> a verification on the part of pipeline that is about to be > >> activated, and if verification succeeds it is applied > >> > >> Somehow I suspect neither is trivial... > > > > I would say it is not, but if you have such a device that does not > > require going through a s_stream(0)/s_stream(1) cycle and all the > > associated re-negotiation and validations, it seems to me nothing > > prevents you from handling this in the driver implementation. Maybe it > > won't look that great, but this seems to be quite a custom design that > > requires all input sources to be linked to your sink pads, their > > format validated all at the same time, power, stream activation and > > internal mux configuration controlled by s_routing. Am I wrong or > > nothing in this series would prevent your from doing this? > > You're right, nothing prevents me from doing a custom hack for my custom > design. It's what I'm doing right now. My concern is whether the > framework will evolve to allow modifying a running pipeline without > custom hacks. > > > tl;dr: I would not make this something the framework should be > > concerned about, as there's nothing preventing you from > > implementing support for such a use case. But again, without a real > > example we can only guess, and I might be overlooking the issue or > > missing some relevant detail for sure. > > I'm a bit surprised in observing that my use case looks so strange, > perhaps yours is so different that we don't quite understand each other. > So below is an example of what I have in mind. Can you explain your use > case too? I'm mostly interested in this series as it allows me to add data lane negotiation at run time. In my case, there are no stream continuity constraints, but I get your point here. > > > Here's a use case. Consider a product that takes 3 camera inputs, > selects one of them and produces a continuous video stream with the > camera image and an OSD on top of it. The selected camera can be changed > at any time (e.g. upon user selection). > > OSD FB ---. > | > .--------. V > Camera 0 -->| | .-----. > Camera 1 -->| MUX |-->| OSD |--> DMA --> /dev/video0 > Camera 2 -->| | `-----' > `--------' > > A prerequisite is obviously that each piece of hardware and software > involved is able to cope with a sudden stream change. Perhaps not that > common, but no rocket science. > > It looks to me that each of these pieces can be modeled as an entity and > the s_routing API is a perfect fit for the mux block. Am I wrong? > Personally, I would say that your muxer driver, if able to switch source without requiring a pipeline restart, should handle it internally. There are specific details that the mux should be able to handle, and we're still pretty vague on the details. As a start, which is the bus type your sources connects to the muxer with? Parallel? CSI-2? How is the video stream multiplexed? with CSI-2 VC? Do you need to control your source power during inactive period? I'm sure there are more questions... I agree a partial pipeline restart might be something to consider, but at the same time I think this is not something strictly required to get this series merged, isn't it? Thanks j > Thanks, > -- > Luca
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