Messages in this thread | | | Date | Tue, 9 Aug 2022 19:04:14 +0530 | Subject | Re: [PATCH 4/8] drm/tidss: Add support for Dual Link LVDS Bus Format | From | Aradhya Bhatia <> |
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Hi Tomi,
On 09-Aug-22 15:21, Tomi Valkeinen wrote: > On 09/08/2022 12:06, Aradhya Bhatia wrote: > >>>> Even in DT, the dss port (for OLDI) connects to the panel port's >>>> endpoint directly. Even in cases of dual link or cloning, it's only a >>>> singular remote-to-endpoint connection between the (OLDI) VP and the >>>> panel port. Hence the requirement of the properties in the earlier >>>> patches of the series. >>> >>> Sorry, I don't follow. If you use cloning, you have two TX outputs, >>> going to two panels, right? So you need two panel DT nodes, and those >>> would connect to two OLDI TX ports in the DSS. >>> > Afaics the existing dual link bridge/panel drivers also use two ports >>> for the connection, so to use the dual link you need two ports in the >>> DSS. >>> >>> I admit I'm not familiar with LVDS dual link, but it's not clear to >>> me how you see the dual OLDI TX being used with other drivers if you >>> have only one port. What kind of setups have you tested? >>> >> In the DTs, the OLDIs are not modeled at all. Since the DSS only has a >> single VP for OLDI, the DT dss port (for OLDI) is connected to a single >> simple-panel node for dual link, bypassing the OLDI TX in DT. I have >> this same OLDI setup and have been testing on this. > > A DSS VP is a DSS internal port, whereas a port node in the DT is an > external port. There doesn't have to be a 1:1 match between those. > > The port in the DT represents some kind of "connector" to the outside > world, which is usually a collection of pins that provide a video bus. > Okay, I now understand what you are saying. Indeed, I was mapping the DSS VP and DT DSS port as 1:1 in my mind, which should not be the case.
> Here, as far as I can see, the DSS clearly has three external ports, two > OLDI ports and one DPI port. > >> I do not have a cloning display setup with me, but I have seen DT DSS >> port connected to one of 2 panel nodes while the other panel (remains as >> a companion panel to the first) without any endpoint connections. Since, >> the OLDI TXes (0 and 1), receive the same clocks and inputs from DSS >> OLDI VP, this 'method' has worked too. > > This, and using simple-panel for dual link with single port connection, > sounds like a hack. > > A practical example: TI's customer wants to use AM625 and THC63LVD1024 > bridge. How does it work? THC63LVD1024 driver uses two LVDS ports for > input, both of which are used in dual-link mode. > Right. There has to be 2 ports for OLDI in DSS, to be connected to 2 ports of a single panel (dual link) or 2 ports of 2 panels (cloning).
>>>> The use of lvds helper functions does not seem feasible in this case, >>>> because even they read DT properties to determine the dual link >>>> connection and those properties need to be a part of a lvds bridge >>>> device. >>> >>> Can you elaborate a bit more why the DRM helpers couldn't be used here? >>> >> The drm_of.c helpers use DT properties to ascertain the presence of a >> dual-link connection. While there wasn't a specific helper to determine >> dual-link or not, the drivers use the odd/even pixel order helper which >> is based on the properties "dual-lvds-odd-pixels" and "dual-lvds-odd- >> pixels". If either of the properties are absent, the helper returns an >> error making the driver to use single link. >> >> These properties are LVDS specific, but they could not be added in the >> DT because there is no OLDI TX DT node for our case. > > If I'm not mistaken, those properties are in the port node, not the > device node, and also, I believe those properties are on the sink side, > so they wouldn't even be in the AM625 data. See, for example: > > arch/arm64/boot/dts/renesas/r8a774c0-ek874-idk-2121wr.dts Yeah, they are indeed on the sink side. I was misunderstood about this. And the onus for properties is not on DSS nodes anymore.
This probably is a different discussion, but since the sink is now responsible for those properties, these should get introduced in the panel-common bindings, right?
The above example has a separate binding, but many dumb dual-link panels will require those properties in panel-common.
> >>>> I have also been considering the idea of implementing a new device >>>> driver for the OLDI TXes, not unlike the renesas' one. That way the >>>> driver could have the properties and the lvds helper functions at their >>>> disposal. I am just slightly unsure if that would allow space for any >>>> conflicts because of the shared register space. >>> >>> No, I don't think new devices are needed here. >> Okay... >> >> I am not quite sure I understand completely what you are recommending >> the OLDI to be. It seems to me that you want the OLDI TXes to be modeled >> as nodes, right? Wouldn't that automatically require some sort of >> standalone driver arrangement for them? Or am I missing something >> important here? > > No, I'm only talking about the DT port nodes. At the moment the AM65x DT > bindings doc says that there are two ports, port@0 for OLDI and port@1 > for DPI. I'm saying AM625 needs three ports. Agreed.
Moreover, I will update the binding to reflect 3 ports for am625-dss.
Regards Aradhya
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