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 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? Regards, Mauro -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
