I would like to know if DSI/LVDS bridge IC is required to support two separate LVDS displays in Verdin iMX8m plus. In the data sheet, it is not stated that the LVDS I/F in the SoM supports two independent single channels. But the block diagram in the date sheet implies that 2 single LVDS channels are supported. Please let me know which one is correct.
Dear @kazu , thanks for reaching out to the Toradex Community!
We haven’t confirmed this but checking NXP documentation, “split” mode should be possible. You would be limited by using single channel each.
Unfortunately, we haven’t tried the split mode yet and we don’t have any device tree’s already implemented with this mode.
You can check all our available device tree overlays here
Another solution is your suggestion of using the DSI-LVDS bridge IC.
Dear @alvaro.tx , thank you for response.
This is a confusing topic. Let me understand it clearly.
As a comparison, Colibri i.MX8X data sheet says that i.MX8X has one display controller with two outputs, which allow driving two independent displays (LVDS1, LVDS2). So, it obviously supports two separate LVDS displays. Is it split-mode or two single modes?
Verdin i.MX8M Plus has three display controllers called LCDIF. For DSI, HDMI, LVDS each. The data sheet does not state that two independent displays are supported in LVDS I/F. To use split-mode, does the application program treat it as a single display I/F and send a mixed stream of display data? It seems to be not an easy task to do.
Yes, I agree that the topic is not clear… I have further checked with our BSP team and it seems that there is a discussion going on since a couple of months ago. This was started through NXP forums: SOM i.MX 8M Plus and a 1920x720 dual LVDS display - NXP Community
Unfortunately, the NXP team hasn’t confirmed this.
Our BSP team feedback: The SoC datasheet doesn’t really mention any of this. The reference manual also doesn’t seem to contain any clear statements. We have strong doubts that this is possible: This so called “split” use case is only mentioned in a single table 13-33 in the TRM. And at other places it clearly mentions “pixels from the single LCDIF display output”. But for a true split mode two separate such display outputs would be needed!
Therefore, we would recommend to use the DSI-LVDS bridge for a second LVDS output.
Thank you for the follow-up. I am a bit confused. If LVDS supports dual channel, then it has enough I/O lines for two single-channels. The question is if it is possible to control the single-channels independently for the two displays (single + single?). The forum topic you mentioned is more about showing images over two physical displays. My goal is to show separate contents on two independent LVDS displays using LVDS LCDIF.
If you find further information, please share with us. The problem with DSI-LVDS bridge is its long lead time.
If LVDS supports dual channel, then it has enough I/O lines for two single-channels.
The question is if it is possible to control the single-channels independently for the two displays (single + single?).
Correct. But this is possibly more a limitation on what is currently supported at Linux. Based on the documentation, in theory seems possible, but maybe at implementation level it requires some development (possibly at driver level).
I wouldn’t recommend this, I personally don’t think it is worth the effort since there is a chance that NXP improves the support of this in the future.
If you find further information, please share with us.
The problem with DSI-LVDS bridge is its long lead time.
I see… What about using an HDMI display in addition to the LVDS display? That way you can directly use the HDMI connector.
Thank you for prompt response and advise. Yes, we started looking into DSI-LVDS, HDMI-LVDS bridges. The reason for not using HDMI displays is that a LVDS display is already selected, and also the use of HDMI connector on the product requires a license fee to pay…
Dear @kazu , we re-evaluated the requirements in case we missed something but unfortunately we are still very confident that the i.MX 8M Plus SoC only supports ONE single LVDS display either in single-channel or dual-channel configuration and such dual-channel can NOT be used in a true split mode to drive two independent displays.
Sorry about this, but you will have to use the other 2 interfaces (DSI or HDMI) for the second LVDS display.
Thank you for the follow-up. I see the whole picture now.