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

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Date:   Thu, 21 Dec 2017 18:36:28 +0200
From:   Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Pavel Machek <pavel@....cz>
Cc:     Sakari Ailus <sakari.ailus@....fi>, robh+dt@...nel.org,
        devicetree@...r.kernel.org, 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,

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