Adrian (a.delete@this.acm.org) on December 11, 2020 12:37 am wrote:
> anonymou5 (no.delete@this.spam.com) on December 10, 2020 3:12 pm wrote:
> > sorry, not interested in the BS portion
> >
> > back to the display problem at hand
> >
> > I see that some C-to-DP cables are bidirectional, i.e. people can drive
> > 4K displays with C ports from a device that has an outgoing DP
> >
> > does this work for C-to-HDMI cables too? anyone? the web isn't so clear on it to me (for now)
> >
> > specifically, what about hooking one of these...
> >
> > https://www.sonnetstore.com/products/egfx-breakaway-puck-560
> >
> > ...to the TB on the Mac, and then driving the 4K LG displays from there, with the aforementioned cables?
> >
> > bonus points if it works for 4 displays, not just 2 -- hence
> > the HDMI question above (as the puck has 3x DP + 1x HDMI)
> >
> > real world tech problems ;-)
>
>
> That one is not an adapter, but an external Radeon GPU, so the same as a second graphic card, connected
> through PCIe over Thunderbolt. As long as the operating system supports it, which should be true
> for any MacOS, you can connect any monitors to it, like to any other graphic card.
>
> The only limitation is that the external graphic card is connected through a 4-lane
> PCIe 3.0 instead of through a 16-lane PCIe 3.0, like an internal card.
>
> It is weird that on that page there is no mention about the size of
> the internal memory, though on other sites it is given as 4 GB.
>
>
> To connect an HDMI monitor to a Thunderbolt or USB Type-C connector, there are 4 possible ways:
>
> 1. If the connector is Thunderbolt, an external graphic card, connected through PCIe
> over Thunderbolt, with a HDMI connector on the external GPU, like in your example
>
> 2. If the connector is Thunderbolt, an adapter from DisplayPort to HDMI, connected
> through DisplayPort over ThunderBolt. The adapter can be a box with Type-C & HDMI connectors,
> or it can be just a cable with Type-C and HDMI connectors at the 2 ends.
>
> 3. If the connector supports the alternate mode DisplayPort of the USB standard, an adapter from DisplayPort
> to HDMI, connected through DisplayPort over Type-C USB. The adapter can be a box with Type-C & HDMI
> connectors, or it can be just a cable with Type-C and HDMI connectors at the 2 ends.
>
> 4. If the connector supports the alternate mode HDMI of the USB standard, an adapter from Type-C
> USB to HDMI, connected through HDMI over Type-C USB. The adapter can be a box with Type-C & HDMI
> connectors, or it can be just a cable with Type-C and HDMI connectors at the 2 ends.
>
>
> The first 3 kinds are common. I have not seen any equipment that supports the 4th kind, with alternate mode
> HDMI, but they might exist, but not for Apple products, as I never heard about Apple supporting this mode.

The problem is that ALL of these assume an HDMI monitor endpoint. That's easy, no-one denies that.
What's problematic is a monitor that doesn't have HDMI, just USB-C alt. That's the problem we are trying to solve (especially if you want to "split" the bandwidth to drive two such monitors. Hence my point that, at least when buying for myself, I'd avoid a monitor with only USB-C as the single input port type.