Hi Geert, On Tue, Jul 17, 2018 at 02:23:16PM +0200, Geert Uytterhoeven wrote: > Hi Jacopo, > > On Tue, Jul 17, 2018 at 2:13 PM jacopo mondi <jacopo@xxxxxxxxxx> wrote: > > I'm replying here, even if a new version of the bindings for this > > chip has been posted[1], as they have the same ports layout. > > > > [1] https://www.spinics.net/lists/linux-renesas-soc/msg29307.html > > > > On Wed, Jun 06, 2018 at 08:34:41AM +0200, Geert Uytterhoeven wrote: > > > Hi Kieran, > > > > > > On Wed, Jun 6, 2018 at 1:34 AM, Kieran Bingham > > > <kieran.bingham+renesas@xxxxxxxxxxxxxxxx> wrote: > > > > Provide device tree binding documentation for the MAX9286 Quad GMSL > > > > deserialiser. > > > > > > > > Signed-off-by: Kieran Bingham <kieran.bingham+renesas@xxxxxxxxxxxxxxxx> > > > > > > Thanks for your patch! > > > > > > > --- /dev/null > > > > +++ b/Documentation/devicetree/bindings/media/i2c/max9286.txt > > > > @@ -0,0 +1,75 @@ > > > > +* Maxim Integrated MAX9286 GMSL Quad 1.5Gbps GMSL Deserializer > > > > + > > > > +Required Properties: > > > > + - compatible: Shall be "maxim,max9286" > > > > + > > > > +The following required properties are defined externally in > > > > +Documentation/devicetree/bindings/i2c/i2c-mux.txt: > > > > + - Standard I2C mux properties. > > > > + - I2C child bus nodes. > > > > + > > > > +A maximum of 4 I2C child nodes can be specified on the MAX9286, to > > > > +correspond with a maximum of 4 input devices. > > > > + > > > > +The device node must contain one 'port' child node per device input and output > > > > +port, in accordance with the video interface bindings defined in > > > > +Documentation/devicetree/bindings/media/video-interfaces.txt. The port nodes > > > > +are numbered as follows. > > > > + > > > > + Port Type > > > > + ---------------------- > > > > + 0 sink > > > > + 1 sink > > > > + 2 sink > > > > + 3 sink > > > > + 4 source > > > > > > I assume the source and at least one sink are thus mandatory? > > > > > > Would it make sense to use port 0 for the source? > > > This would simplify extending the binding to devices with more input > > > ports later. > > > > I see your point, but as someone that has no idea how future chips could look > > like, I wonder why having multiple outputs it's more un-likely to > > happen than having more inputs added. > > I also don't know. > I was just thinking "What if another chip has less or more sinks?". > > > Do you have any suggestion on how we can handle both cases? > > Instead of having a single "ports" subnode, you could split it in two subnodes, > "sinks" and "sources"? I don't know if that's feasible. > Maybe I didn't get you here, and sorry to repeat something obvious for you but, that would be against basic assumptions both in fwnode/of framework and in media framework too. See the graph.txt documentation and video_interfaces.txt, the layout with a single 'ports' node with multiple 'port' sub-nodes is not avoidable, afaik. What is not -theoretically- forbidden is to have port subnodes with multiple endpoints, which is also used as an example in multiple places in the documentation files I mentioned above. Unfortunately, as we experienced with the ADV748x and the R-Car CSI-2 receiver upstreaming effort, the v4l2-async framework relies on matching on the remote endpoint's parent device node, and Kieran and Niklas had to use a custom endpoint matching logic for the R-Car CSI-2 and adv748x combo, something I'm sure nobody wants to repeat here. We said that multiple times that we would like to tackle this limitation (if that's limitation) in the v4l2_async framework, maybe if GMSL-like devices with multiple input/output ports comes out, we might have enough motivation to do that ;) ? Thanks j > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds
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