Re: [PATCH] devicetree: Add video bus switch

[Ivaylo Dimitrov]

Hi,

On 20.12.2017 19:54, Laurent Pinchart wrote:
> Hi Pavel,
>
> On Saturday, 4 February 2017 23:56:10 EET Pavel Machek wrote:
> > Hi!
> >
> > > > > > +Required properties
> > > > > > +===================
> > > > > > +
> > > > > > +compatible	: must contain "video-bus-switch"
> > > > >
> > > > > How generic is this? Should we have e.g. nokia,video-bus-switch? And
> > > > > if so, change the file name accordingly.
> > > >
> > > > Generic for "single GPIO controls the switch", AFAICT. But that should
> > > > be common enough...
> > >
> > > Um, yes. Then... how about: video-bus-switch-gpio? No Nokia prefix.
> >
> > Ok, done. I also fixed the english a bit.
> >
> > > > > > +reg		: The interface:
> > > > > > +		  0 - port for image signal processor
> > > > > > +		  1 - port for first camera sensor
> > > > > > +		  2 - port for second camera sensor
> > > > >
> > > > > I'd say this must be pretty much specific to the one in N900. You
> > > > > could have more ports. Or you could say that ports beyond 0 are
> > > > > camera sensors. I guess this is good enough for now though, it can be
> > > > > changed later on with the source if a need arises.
> > > >
> > > > Well, I'd say that selecting between two sensors is going to be the
> > > > common case. If someone needs more than two, it will no longer be
> > > > simple GPIO, so we'll have some fixing to do.
> > >
> > > It could be two GPIOs --- that's how the GPIO I2C mux works.
> > >
> > > But I'd be surprised if someone ever uses something like that
> > > again. ;-)
> >
> > I'd say.. lets handle that when we see hardware like that.
> >
> > > > > Btw. was it still considered a problem that the endpoint properties
> > > > > for the sensors can be different? With the g_routing() pad op which is
> > > > > to be added, the ISP driver (should actually go to a framework
> > > > > somewhere) could parse the graph and find the proper endpoint there.
> > > >
> > > > I don't know about g_routing. I added g_endpoint_config method that
> > > > passes the configuration, and that seems to work for me.
> > > >
> > > > I don't see g_routing in next-20170201 . Is there place to look?
> > >
> > > I think there was a patch by Laurent to LMML quite some time ago. I
> > > suppose that set will be repicked soonish.
> > >
> > > I don't really object using g_endpoint_config() as a temporary solution;
> > > I'd like to have Laurent's opinion on that though. Another option is to
> > > wait, but we've already waited a looong time (as in total).
> >
> > Laurent, do you have some input here? We have simple "2 cameras
> > connected to one signal processor" situation here. We need some way of
> > passing endpoint configuration from the sensors through the switch. I
> > did this:
>
> Could you give me a bit more information about the platform you're targeting:
> how the switch is connected, what kind of switch it is, and what endpoint


http://plan9.stanleylieber.com/hardware/n900/n900.schematics.pdf, on 
page 2, see N5801 and N5802.

> configuration data you need ?
>
> > > > @@ -415,6 +416,8 @@ struct v4l2_subdev_video_ops {
> > > >                           const struct v4l2_mbus_config *cfg);
> > > >      int (*s_rx_buffer)(struct v4l2_subdev *sd, void *buf,
> > > >                         unsigned int *size);
> > > > +   int (*g_endpoint_config)(struct v4l2_subdev *sd,
> > > > +                       struct v4l2_of_endpoint *cfg);
> >
> > Google of g_routing tells me:
> >
> > 9) Highly reconfigurable hardware - Julien Beraud
> >
> > - 44 sub-devices connected with an interconnect.
> > - As long as formats match, any sub-device could be connected to any
> > - other sub-device through a link.
> > - The result is 44 * 44 links at worst.
> > - A switch sub-device proposed as the solution to model the
> > - interconnect. The sub-devices are connected to the switch
> > - sub-devices through the hardware links that connect to the
> > - interconnect.
> > - The switch would be controlled through new IOCTLs S_ROUTING and
> > - G_ROUTING.
> > - Patches available:
> >   http://git.linuxtv.org/cgit.cgi/pinchartl/media.git/log/?h=xilinx-wip
> >
> > but the patches are from 2005. So I guess I'll need some guidance here...
>
> You made me feel very old for a moment. The patches are from 2015 :-)
>
> > > I'll reply to the other patch containing the code.

Regards,
Ivo