Hello Mauro,
On 02/26/2016 09:13 AM, Mauro Carvalho Chehab wrote:
We had some discussions on Feb, 12 about how to represent connectors via
the Media Controller:
https://linuxtv.org/irc/irclogger_log/v4l?date=2016-02-12,Fri&sel=31#l27
We tried to finish those discussions on the last two weeks, but people
doesn't seem to be available at the same time for the discussions. So,
let's proceed with the discussions via e-mail.
So, I'd like to do such discussions via e-mail, as we need to close
this question next week.
QUESTION:
========
How to represent the hardware connection for inputs (and outputs) like:
- Composite TV video;
- stereo analog audio;
- S-Video;
- HDMI
Problem description:
===================
During the MC summit last year, we decided to add an entity called
"connector" for such things. So, we added, so far, 3 types of
connectors:
#define MEDIA_ENT_F_CONN_RF (MEDIA_ENT_F_BASE + 10001)
#define MEDIA_ENT_F_CONN_SVIDEO (MEDIA_ENT_F_BASE + 10002)
#define MEDIA_ENT_F_CONN_COMPOSITE (MEDIA_ENT_F_BASE + 10003)
However, while implementing it, we saw that the mapping on hardware
is actually more complex, as one physical connector may have multiple
signals with can eventually used on a different way.
One simple example of this is the S-Video connector. It has internally
two video streams, one for chrominance and another one for luminance.
It is very common for vendors to ship devices with a S-Video input
and a "S-Video to RCA" cable.
At the driver's level, drivers need to know if such cable is
plugged, as they need to configure a different input setting to
enable either S-Video or composite decoding.
So, the V4L2 API usually maps "S-Video" on a different input
than "Composite over S-Video". This can be seen, for example, at the
saa7134 driver, who gained recently support for MC.
Additionally, it is interesting to describe the physical aspects
of the connector (color, position, label, etc).
Proposal:
========
It seems that there was an agreement that the physical aspects of
the connector should be mapped via the upcoming properties API,
with the properties present only when it is possible to find them
in the hardware. So, it seems that all such properties should be
optional.
However, we didn't finish the meeting, as we ran out of time. Yet,
I guess the last proposal there fulfills the requirements. So,
let's focus our discussions on it. So, let me formulate it as a
proposal
Thanks for writing down as a proposal what was discussed over IRC.
We should represent the entities based on the inputs. So, for the
already implemented entities, we'll have, instead:
#define MEDIA_ENT_F_INPUT_RF (MEDIA_ENT_F_BASE + 10001)
#define MEDIA_ENT_F_INPUT_SVIDEO (MEDIA_ENT_F_BASE + 10002)
#define MEDIA_ENT_F_INPUT_COMPOSITE (MEDIA_ENT_F_BASE + 10003)
The MEDIA_ENT_F_INPUT_RF and MEDIA_ENT_F_INPUT_COMPOSITE will have
just one sink PAD each, as they carry just one signal. As we're
describing the logical input, it doesn't matter the physical
connector type. So, except for re-naming the define, nothing
changes for them.
Devices with S-Video input will have one MEDIA_ENT_F_INPUT_SVIDEO
per each different S-Video input. Each one will have two sink pads,
one for the Y signal and another for the C signal.
So, a device like Terratec AV350, that has one Composite and one
S-Video input[1] would be represented as:
https://mchehab.fedorapeople.org/terratec_av350-modified.png
[1] Physically, it has a SCART connector that could be enabled
via a physical switch, but logically, the device will still switch
from S-Video over SCART or composite over SCART.
More complex devices would be represented like:
https://hverkuil.home.xs4all.nl/adv7604.png
https://hverkuil.home.xs4all.nl/adv7842.png
NOTE:
The labels at the PADs currently can't be represented, but the
idea is adding it as a property via the upcoming properties API.
Anyone disagree?
What you described is what I understood that was the last proposal
and I believe everyone agreed that it was the way to move forward.
I've just one question, why the PAD's labels / symbolic names will
be added as a property instead of just having a name or label field
in struct media_pad?
For example, in the Terratec AV350 chip you mentioned, the AIP1{A,B}
source pads are real pins in the tvp5150 package and are documented
in the datasheet and a S-Video connector will always have a Y and C
sinks pads for the 2 signals and a Composite connector a single pad.
So why can't the driver just set those when creating the connectors
entities? Or maybe I'm misunderstanding how the properties API work.
Regards,
Mauro
Best regards,
--
Javier Martinez Canillas
Open Source Group
Samsung Research America
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