linux-kernel - Re: [RESEND PATCH v6 1/1] Added Digiteq Automotive MGB4 driver

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Message-ID: <313827c0-3b7a-e70a-b281-cbb5f68e6fd2@xs4all.nl>
Date:   Tue, 13 Jun 2023 14:26:34 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Martin Tůma <tumic@...see.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Martin Tůma <martin.tuma@...iteqautomotive.com>
Subject: Re: [RESEND PATCH v6 1/1] Added Digiteq Automotive MGB4 driver

On 12/06/2023 16:36, Martin Tůma wrote:
> On 12. 06. 23 10:42, Hans Verkuil wrote:
>> On 08/06/2023 13:16, Martin Tůma wrote:
>>> Hi,
>>> This is the "technical" part of my response, comments bellow:
>>>
>>> On 07. 06. 23 10:41, Hans Verkuil wrote:
>>>> Hi Martin,
>>>>
>>>> Some comments below:
>>>>
>>>> On 24/05/2023 13:21, tumic@...see.org wrote:
>>>>> From: Martin Tůma <martin.tuma@...iteqautomotive.com>
>>>
>>>>> diff --git a/Documentation/admin-guide/media/mgb4.rst b/Documentation/admin-guide/media/mgb4.rst
>>>>> new file mode 100644
>>>>> index 000000000000..77db2fa64ab4
>>>>> --- /dev/null
>>>>> +++ b/Documentation/admin-guide/media/mgb4.rst
>>>>> @@ -0,0 +1,352 @@
>>>>> +.. SPDX-License-Identifier: GPL-2.0
>>>>> +
>>>>
>>>> Perhaps it is a good idea to start with a high level overview of the
>>>> hardware blocks. That might help understand how the various parts are
>>>> connected.
>>>>
>>>
>>> This is the "admin-guide" documentation and I'm not sure if the admins (= the card users) are interested in some hardware blocks description. I can for sure ad some basic info like that the card (with
>>> the given module) has two inputs and two outputs, but if you hold the card in your hands while installing it into the PCIe slot you definitely notice that ;-)
>>
>> True, but I don't have that module :-).
>>
>> I assume the inputs (and also outputs) are mutually exclusive? I.e., only one at a time can be active?
>>
>> But it is also possible to switch between the inputs/outputs dynamically if you want?
>>
>> Right now it is hard coded through this property, but I assume there is a reason these
>> modules have two inputs and two outputs, so it is odd that it is not possible use
>> VIDIOC_S_INPUT/S_OUTPUT to toggle between them.
>>
> 
> With the current modules, you can not even theoretically (after changing the FPGA bitstream) change the outputs to inputs or vice versa as the the serializers/deserializers are hardcoded on the modules.

I think you misunderstand me.

Let's keep it simple: a source is connected to input 0 and you capture from it with V4L2.

Can I dynamically switch to input 1 and capture from that? I.e., each input has a
different source connected to it, so userspace can select from which input to capture.

Right now it appears that V4L2 just advertises a single input. And the input_id
property is read-only. So that means that input 1 is effectively unusable with
the current driver, or am I missing something?

> 
> I can post here some photo of the card, if it is ok to send image attachement to the mailing list so you have some image of what we are talking about. Or I can even show you the card live when you are
> in Prague in few days.

Actually, I'd like that! We'll meet there anyway, so that's a good opportunity to
see the real deal :-)

Regards,

	Hans