Hi Javier, On Friday 26 February 2016 10:13:48 Javier Martinez Canillas wrote: > 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. Creating input entities instead of connector entities was indeed proposed, but when we closed the meeting I was still pondering on the implications, I wouldn't call that an agreement on 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? Same reason as for entity labels in general, using the property API will avoid wasting space for an optional string property that would otherwise have to be stored in every pad structure (and we'll have lots of them). Another additional benefit of the property API (or at least of the way I envision it) is that we won't be bound by a predefined short(ish) label maximum length. > 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. Another point that needs to be discussed, when we'll talk about pad labels, is how to differentiate pads from userspace in general. Applications will need to refer to pads when using kernel APIs (to set formats for instance), so they will need a way to find the pad(s) they're interested in. Given that pad IDs are not stable we can't rely on them to look a pad up. So far we've always used pad indexes for this purpose, and I would prefer keeping that as the prime pad lookup method instead of making it string-based. This doesn't preclude adding labels for informative purpose of course. I wonder if we can keep this topic separate from the connector entities discussion, or if it needs to be discussed already. For instance if we decide to model entities in such a way that the number of pads can vary depending on the way the entity is instantiated, we'll have to make sure already that we can offer userspace a way to locate pads. This doesn't have to involve labels, but pad look up must be considered. -- Regards, Laurent Pinchart -- 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
