Re:VESA Publishes DisplayPort 2.0 Video Standard
by colechristensen on Wednesday June 26, 2019 @03:10PM
(#20288153)
You can (should) do this at a lower level by having the physical layer electrically detect that both ends of a cable are plugged in (bonus points for detecting the type of thing on the other end). Can be done as simply as testing for varying resistance levels between pairs of pins. USB does this for detecting OTG master/slave relationships for example. I think DVI also does this in some way. I remember having to do something to the plugs to get Linux to enable the GPUs in my mining days.
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Re:VESA Publishes DisplayPort 2.0 Video Standard
by simias on Wednesday June 26, 2019 @05:04PM
(#20289175)
This exists in HDMI and I'm pretty sure it has to exist in newer standards. Generally the problem is that figuring out that something is plugged is not enough, you also need to know what is plugged, what resolutions it supports etc...
I don't know how DP does it but previously there was a good old I2C link in the cable that was used to figure out what the screen supported[1]. You only needed an I2C EPROM on the other hand containing the various modes. Without this the computer on the other end can't really prepare itself properly, preallocate the framebuffers etc...
Since the EPROM requires very little energy it might even work if the monitor is not powered, just using the +5V coming from the HDMI cable.
Re:VESA Publishes DisplayPort 2.0 Video Standard
by pault on Wednesday June 26, 2019 @04:37PM
(#20288880)
>I remember having to do something to the plugs to get Linux to enable the GPUs in my mining days.
You also have to do this with certain desktop streaming solutions if the host PC doesn't have a display. You can buy fake HDMI connectors that are just a cap over the HDMI port to trick the video card into thinking there is a display attached.