linux-kernel - Re: [PATCH] devicetree: Add video bus switch

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Message-ID: <75694885.3PuLWzx4qN@avalon>
Date:   Wed, 20 Dec 2017 19:54:12 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Sakari Ailus <sakari.ailus@....fi>, robh+dt@...nel.org,
        devicetree@...r.kernel.org, ivo.g.dimitrov.75@...il.com,
        sre@...nel.org, pali.rohar@...il.com, linux-media@...r.kernel.org,
        galak@...eaurora.org, mchehab@....samsung.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] devicetree: Add video bus switch

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 
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,

Laurent Pinchart