L5 Display Port to Auto Head Unit HDMI-In

Hardware Librem 5
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I want to replace the radio in my old truck with a Linux head unit featuring an HDMI-In port. Presumably, I could control/see/hear the L5 from the head unit. In my head, this seems easy enough… if I mount the L5 directly over the cold air vent and find a USB splitter that charges the L5 while simultaneously allowing Display Port out.

Is this possible or a delirious fantasy?

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I would look very closely at the USB splitter to make sure that it actually supports Display Port altmode.

Better would be a head unit that can deliver power directly over USB.

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In my experience, hdmi out is the easy part.

It’s harder to find a setup that provides enough power to actually charge the phone…

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The relevant variable is how much current does the dock provide under 5V. It’s not that hard to find ones that will charge the phone, but it isn’t hard to find ones that won’t either.

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Does this mean that the head unit has a touch screen? If so then HDMI by itself won’t work. The head unit would need a separate USB port to send touch events back to the phone (and you would therefore need a dock to manage that, and you get into compatibility testing). Hence it would be better to have a head unit with just a USB-C port so that all you need is a USB-C to USB-C USB cable and it handles touch events (head unit to phone), power (head unit to phone) and video (phone to head unit).

Of course the head unit itself needs to get power from somewhere. I have assumed that it is independently powered.

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That’s the idea.

I’m off to find a head unit with USB-C that supports PD-out and Display Port Alt-Mode-In. All of the Linux head units I find are locked down so you can’t install packages. I’ll settle for on that will let me display/control the L5… if I can find one.

If not, I may have to build a custom head unit from a Pi, Odroid or other small computer. I think I have the skills but I doubt I have the time.

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Here’s a compatibility list for USB-C PD hubs specifically for the L5.
It’s far from exhaustive but maybe it helps.

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Hmm… very helpful, especially since I haven’t found suitable head units. However, it appears there are small (7 or 8") touchscreen monitors available with USB-C DP ALT MODE.

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