On 02/26/2016 01:13 PM, 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 > > 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. What if my device has an SVIDEO output (e.g. ivtv)? 'INPUT' denotes the direction, and I don't think that's something you want in the define for the connector entity. As was discussed on irc we are really talking about signals received or transmitted by/from a connector. I still prefer F_SIG_ or F_SIGNAL_ or F_CONN_SIG_ or something along those lines. I'm not sure where F_INPUT came from, certainly not from the irc discussion. > 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. I think this is a separate discussion. It's not needed for now. When working on the adv7604/7842 examples I realized that pad names help understand the topology a lot better, but they are not needed for the actual functionality. > > Anyone disagree? I agree except for the naming. Regards, Hans -- 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
