Re: [RFC PATCH 1/3] [media] v4l2-mc.h: Add a S-Video C input PAD to demod enum

[Hans Verkuil <hverkuil@xs4all.nl>]

On 03/21/2016 07:34 PM, Mauro Carvalho Chehab wrote:
> Em Mon, 21 Mar 2016 15:24:00 -0300
> Javier Martinez Canillas <javier@osg.samsung.com> escreveu:
> 
>> Hello Hans,
>>
>> On 03/21/2016 03:08 PM, Hans Verkuil wrote:
>>> On 03/21/2016 06:50 PM, Mauro Carvalho Chehab wrote:
>>>> Hi Hans,
>>>>
>>>> Em Mon, 21 Mar 2016 17:01:43 +0100
>>>> Hans Verkuil <hverkuil@xs4all.nl> escreveu:
>>>>
>>>>>> A reasonable solution to simplify converting legacy drivers without creating
>>>>>> these global ugly pad indices is to add a new video (and probably audio) op
>>>>>> 'g_pad_of_type(type)' where you ask the subdev entity to return which pad carries
>>>>>> signals of a certain type.  
>>>>>
>>>>> This basically puts a layer between the low-level pads as defined by the entity
>>>>> and the 'meta-pads' that a generic MC link creator would need to handle legacy
>>>>> drivers. The nice thing is that this is wholly inside the kernel so we can
>>>>> modify it at will later without impacting userspace.
>>>>
>>>> I prepared a long answer to your email, but I guess we're not at the
>>>> same page.
>>>>
>>>> Let be clear on my view. Please let me know where you disagree:
>>>>
>>>> 1) I'm not defending Javier's patchset. I have my restrictions to
>>>> it too. My understanding is that he sent this as a RFC for feeding
>>>> our discussions for the media summit.
>>>>
>>>> Javier, please correct me if I'm wrong.
>>>>
>>
>> That's correct. I wanted to have some patches that were aligned to what
>> were discussed so far in order to have more examples to contribute in
>> the media summit discussion (since I won't be there).
>>
>> The patches are RFC and not meant to upstream since there are too many
>> open questions. I just hoped that having more examples could help of
>> them. I was specially interested in the DT bindings using OF graph to
>> lookup the connectors and the level of detail there.
>>
>>>> 2) I don't understand what you're calling as "meta-pads". For me, a
>>>> PAD is a physical set of pins. 
>>>
>>> Poorly worded on my side. I'll elaborate below.
>>>
>>>> 3) IMO, the best is to have just one PAD for a decoder input. That makes
>>>> everything simple, yet functional.
>>>>
>>>> In my view, the input PAD will be linked to several "input connections".
>>>> So, in the case of tvp5150, it will have:
>>>>
>>>> 	- composite 1
>>>> 	- composite 2
>>>> 	- s-video
>>>>
>>>> 4) On that view, the input PAD is actually a set of pins. In the
>>>> case of tvp5150, the pins that compose the input PADs are
>>>> AIP1A and AIP1B.
>>>>
>>>> The output PAD is also a set of pins YOUT0 to YOUT7, plus some other
>>>> pins for sync. Yet, it should, IMHO, have just one output PAD at
>>>> the MC graph.
>>>
>>> Indeed. So a tvp5150 has three sink pads and one source pad (pixel port).
>>
>> Why 3 sink pads? Are we going to model each possible connection as a PAD
>> instead of an entity or are you talking about physical pins? Because if
>> is the latter, then the tvp5150 has only 2 (Composite1 shares S-Video Y
>> and Composite2 shares C signal).
>>
>>> Other similar devices may have different numbers of sink pads (say four
>>> composite sinks and no S-Video sinks). So the pads the entity creates
>>> should match what the hardware supports.
>>>
>>> So far, so good.
>>>
>>
>> I'm confused. I thought that the latest agreed approach was to model the
>> actual connection signals and input pins as PADs instead of a simplied
>> model that just each connection as a sink.
>>  
>>> If we want to create code that can more-or-less automatically create a MC
>>> topology for legacy drivers, then we would like to be able to map a high-level
>>> description like 'the first S-Video sink pad' into the actual pad. So you'd
>>> have a 'MAP_PAD_SVID_1' define that, when passed to the g_pad_of_type() op
>>> would return the actual pad index for the first S-Video sink pad (or an error
>>> if there isn't one). That's what I meant with 'meta-pad' (and let's just
>>> forget about that name, poor choice from my side).
>>>
>>
>> Can you please provide an example of a media pipeline that user-space should
>> use with this approach? AFAICT whatever PADs are created when initiliazing
>> the PADs for an entity, will be exposed to user-space in the media graph.
>>
>> So I'm not understading how it will be used in practice. I don't mean that
>> your approach is not correct, is just I'm not getting it :)
>>
>>> What I think Javier's patch did was to require subdevs that have an S-Video pad
>>> to use the DEMOD_PAD_C_INPUT + IF_INPUT pad indices for that. That's really
>>> wrong. The subdev driver decides how many pads there are and which pad is
>>> assigned to which index. That shouldn't be forced on them from the outside
>>> because that won't scale.
>>>
>>
>> Yes, that was something that Mauro suggested in [0] as a possible approach
>> but I also was not sure about it and mentioned in the patch comments.
>>
>>> But you can make an op that asks 'which pad carries this signal?'. That's fine.
>>>
>>> I hope this clarifies matters.
>>>
>>> Regards,
>>>
>>> 	Hans
>>>
>>
>> [0]: http://www.spinics.net/lists/linux-media/msg98042.html
> 
> Yeah, I proposed that, but, after more thinking, it seems easier to
> just use a single sink pad for all supported inputs, just like what's
> there today.
> 
> We'll need to do something different for HDMI, as the HDMI input
> may have signals like CEC that would be going through different
> chips, but for TV decoders that have just composite/RF/s-video
> inputs, I don't see any need to make the model complex.

Also devices like the adv7604 have multiple HDMI inputs, and although only one
HDMI input will go out to the pixelport, the others are still used for EDID
and HDCP processing and hotplug detect, etc. So using a single pad won't
work there.

Regards,

	Hans