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Comment by ianlevesque | Hacker News Reader

I really want to feel that way too (particularly compared to HDMI) but I seem to have so many weird issues that just never existed with DVI. On my work issued M1 Studio for example my displays (bog standard Dell 4K) commonly come up at 30hz or don’t get detected at all until an unplug and replug. I’ve tried all manner of cables and adapters and it’s just not reliable.

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This is a macOS issue. In my experience macOS handles DP much worse than windows. Windows will keep asking the device for its information, while macOS waits for the device to inform the OS. This can cause issues with monitor detection, as you're experiencing.

Does macOS still not support DP-MST properly?

Properly? I thought not at all.

Apparently, if you connect two identical monitors to a mac via dp-mst, it will display the same image on both monitors.

I'm not sure if it's intentional, but it is at least giving an image.

Doesn't support on purpose, though on intel macs alternative OSes could use it.

DDC is also fraught with peril when you want to change settings from OS on non-Apple display.

I had a similar issue with HP 4k displays and docks with M1 MacBooks. The was a MacOS update at some point that broke how these devices work through USB-C. One day they worked, the next they didn’t unless you direct connect to the monitor via HDMI.

It’s really irritating, as we bought these displays specifically because the previous Dell displays didn’t work well with Macs.

I never isolated it because I hadn’t been to that office for 4-5 months during the pandemic. It’s also miserable as the logging for this stuff sucks and nobody really understands how this stuff works. One of my colleagues had success with a thunderbolt dock.

I'm also constantly having issues with DisplayPort that I don't recall ever having with HDMI. The current one is the external monitor just randomly loses the connection and it's a coinflip if I can restore it without rebooting. Usually happens 2-3 times per day.

Just works for me using open graphics drivers on linux, lots of different cards/displays/displayport revisions. HDMI tends to be weirder, at least on linux, with things like HDCP (EDONTCARE) and color space problems.

> On my work issued M1 Studio for example my displays

Do they behave any better if you only have one plugged in at a time? MacOS seems to have problems with multiple identical displays.

They do. But that’s insane for a $5000 desktop computer that claims to support five displays (I’m using two), and honestly shouldn’t be possible. How complicated do we have to make a protocol for moving pixels to a screen?

The protocol is great and works just fine. The problem is with the OS you're using. Install Windows on the same machine and it'll work fine.

Maybe it will, maybe it won't.

My HP laptop with integrated Intel graphics and an HP USB-C dock would have me do a dance of unplugging and replugging the DP monitor at the right time to get 4k@60Hz under Windows. No, plugging it while the PC was running didn't work; for some reason, it was the unplug/replug action which did the trick.

Worked perfectly fine under Linux. Then a Windows or Intel driver update mostly fixed it. Now I "only" get weird "out of range" or a garbled screen when waking from sleep sometimes [0], which usually goes away by switching inputs back and forth on the monitor. Still works fine under Linux.

On the other hand, HDMI via the same dock gives weird-looking colors under Windows, but it always worked at 4k@60. Because of the colors, I never actually used it, so I don't know if it survived a sleep/wake cycle. Never bothered to try HDMI under Linux, though.

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[0] It seems related to how long the PC has been sleeping. If it's only a few minutes, it's OK (say going to the bathroom or similar - default windows settings are quite aggressive for putting the pc to sleep). But if it's longer, like an hour or so, I'd say it's 50-50 whether the screen works properly.

DP sometimes has issues with plug detect on pin 20, using cables with only 19 pins help.

I don't know how many pins my cable has, and never knew there was any such difference. It's the one that came with the monitor.

I chalked it up to a driver issue, since the exact same hardware works great on Linux.

I also have a separate, random Chinese dock off Amazon, which I couldn't get to work under Windows with that particular laptop. It works fine under Linux on that same laptop, and also works fine under Windows with a different, AMD-based laptop.

I haven't tried it in a while, but right after it started working with the HP dock, this particular dock was still not working at all.

It is possible GPU just does not sleep on Linux.

I was going to say “install Windows or Linux” but decided against including the latter bit because I didn’t have sufficient firsthand knowledge of the hardware compatibility story there. I should have trusted my gut ;)

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