Displayport: A Better Video Interface • Hacker News Board

Re: Displayport: A Better Video Interface

#111

Post by bpye » Tue, Jul 11, 2023, 4:51 PM UTC

jon-wood wrote: post #97

bpye wrote: post #74

Earlier quoted context omitted.

Well except for some of the Apple Silicon machines. The M1 (and maybe M2?) only have two video output blocks, of which one is already used for the internal display. It’s honestly the biggest complaint I have about my M1 MBP. Yes DisplayLink or whatever it’s called exists but the performance is bad.

I assume you got one of the original M1 MBPs. The more recent models have more display blocks. M1 Pro can drive two external displays, and I think the M1 Max can do three or four. I’m still slightly pissed Apple ever shipped the original M1 MBPs, they were horrible machines.

It is really my only complaint about it, and since I needed a new laptop at the time it still made sense. I would definitely rather one of the 14” ones now - but not enough to buy a new device.

Re: Displayport: A Better Video Interface

#112

Post by stephenr » Tue, Jul 11, 2023, 4:51 PM UTC

bpye wrote: post #74

stephenr wrote: post #67

Earlier quoted context omitted.

Technically macOS does support MST. But it only supports it to stitch together for a single display. It does not support daisy chaining two displays. Thankfully, every Mac for the last 7 years has Thunderbolt3 at least, so getting dual-4K-display from a single port/cable is still very doable, you just need a TB3 to dual DisplayPort or HDMI adapter.

Well except for some of the Apple Silicon machines. The M1 (and maybe M2?) only have two video output blocks, of which one is already used for the internal display. It’s honestly the biggest complaint I have about my M1 MBP. Yes DisplayLink or whatever it’s called exists but the performance is bad.

But - and I can't believe I forgot this in my other reply - this is one thing that really grinds my gears about Apple's releases since 2018, on everything except the Mac Pro (both 2019 and 2023).

They hard-code one DisplayPort stream to *something* other than Thunderbolt.

On laptops, they hard-code one via eDP to the display, which is useless if it's in clamshell mode.

On Mac Mini, Mac Studio, and the MacBook Pro with HDMI port, one stream from the GPU is hard-coded to the HDMI port. If you want maximum displays, always has to be from HDMI.

But neither the 2019 or 2023 Mac Pro have this limitation. Even on the 2019 model where the HDMI ports were physically on the card - they could route all video streams via system TB3 ports.

I just checked and the base M2 Mini, and the M2 Pro MBP seem to finally allow using two video streams over the TB4 ports, - but the M2 Ultra Studio, with the exact same SoC as the M2 Ultra Mac Pro, still has this stupid artificial limit.

Re: Displayport: A Better Video Interface

#113

Post by [deleted] » Tue, Jul 11, 2023, 4:51 PM UTC

remix2000 wrote: post #23

With HDMI, I have both video and audio traveling over a single cable. That is _extremely_ convenient. DP _theoretically_ supports audio too, but AFAIK that's not widely implemented.

[deleted]

Re: Displayport: A Better Video Interface

#114

Post by hazebooth » Tue, Jul 11, 2023, 4:52 PM UTC

xxpor wrote: post #108

tivert wrote: post #77

Are there any KVM switches that do Displayport well (i.e. where switching between inputs does not look like a display disconnect to the PC)? I'm still using HDMI because I like to share my home multi-monitor setup between my personal machine and my work laptop, and the KVM switches are able to fool the PCs into thinking the monitor are always connected. Years ago I tried a Displayport switch, but it could not -- I as…

The magic words you're looking for are "EDID emulation". The KVM will continue to send the EDID data from the monitor even after you've switched away, which will fix that issue. It's relatively uncommon and not always implemented super well, but it's a requirement for any DP KVM to be not super annoying IMO. There was one particular KVM brand that was supposed to do it well whose name is escaping me now :/. I was loo…

Were you thinking of Level1techs?

https://store.level1techs.com/products/14-kvm-switch-triple-...

Re: Displayport: A Better Video Interface

#115

Post by xxpor » Tue, Jul 11, 2023, 4:52 PM UTC

yellowapple wrote: post #93

londons_explore wrote: post #66

Earlier quoted context omitted.

If this were true, then people would be running datacenter networking over HDMI. Data is data - there is no benefit to designing two entirely different transport mechanisms for video vs other data. You could argue that video data has a deadline to meet - but ethernet already has lots of mechanisms for QoS and bandwidth reservations to make sure that someones torrents don't interrupt something latency sensitive. Sure,…

> If this were true, then people would be running datacenter networking over HDMI. Why would they? If they need more bandwidth than what Ethernet provides, they'd probably just bite the bullet and go with fiber. ...which punts the previous question to why the industry hasn't gone all-in with fiber optic display connectors, like it has with TOSLINK for S/PDIF in the audio world.

TOSLINK/S/PDIF is way out of date and no one uses it any more. Ironically, because it doesn't have enough bandwidth for things like Atmos.

Re: Displayport: A Better Video Interface

#116

Post by hot_gril » Tue, Jul 11, 2023, 4:52 PM UTC

Aaargh20318 wrote: post #83

Perz1val wrote: post #65

Earlier quoted context omitted.

It's not an OS problem, that's how DP is supposed to work and that's in fact stupid

It’s an OS problem for not handling monitors being disconnected and reconnected properly. What is stupid is having half your windows unreachable because they are on a monitor that is turned off. How does that help anyone? Imagine how annoying it would be on a laptop? I use my laptop in a meeting, and have a few windows open on its screen, then I arrive at my desk and plug in my 2 external monitors and keep my laptop…

Makes sense to move the windows if you close a laptop lid, but not if you turn off a monitor. You can't disconnect the laptop screen, but you can easily disconnect the monitor.

I have a cheap laptop that doesn't understand a turned-off monitor as unusable, and it's actually way nicer that way.

Re: Displayport: A Better Video Interface

#117

Post by xxpor » Tue, Jul 11, 2023, 4:54 PM UTC

hazebooth wrote: post #114

xxpor wrote: post #108

Earlier quoted context omitted.

The magic words you're looking for are "EDID emulation". The KVM will continue to send the EDID data from the monitor even after you've switched away, which will fix that issue. It's relatively uncommon and not always implemented super well, but it's a requirement for any DP KVM to be not super annoying IMO. There was one particular KVM brand that was supposed to do it well whose name is escaping me now :/. I was loo…

Were you thinking of Level1techs? https://store.level1techs.com/products/14-kvm-switch-triple-...

I'm 90% sure it was, but it looks like they did a major UI update to the site so it's not triggering the "that was it!" lightbulb in my brain.

Re: Displayport: A Better Video Interface

#118

Post by hot_gril » Tue, Jul 11, 2023, 4:55 PM UTC

lucideer wrote: post #24

Veliladon wrote: post #17

HDMI predates DP by 5 years, switching wouldn't enable any specific use case, and that 5 years head start means HDMI has market inertia. Yes we should use it because it's better but the practicality? There's so much gear that's HDMI that would have to be replaced or require new active adaptors. It's so much industry and consumer effort for such a marginal gain.

Forget all the other pros/cons - MST makes it worth any industry & consumer effort alone.

How many people use multiple external displays? For the power users who do, there are already good enough solutions.

Re: Displayport: A Better Video Interface

#119

Post by crazygringo » Tue, Jul 11, 2023, 4:55 PM UTC

> Just like most digital interfaces nowadays, DisplayPort sends its data in packets. This might sound like a reasonable expectation, but none of the other popular video-carrying interfaces use packets in a traditional sense – VGA, DVI, HDMI and laptop panel LVDS all work with a a stream of pixels at a certain clock rate.

Funny, a stream of data at a constant rate makes much more sense to me intuitively than packets, specifically for uncompressed video.

Are there any downsides to packetization, like increased latency or dropped frames or anything? Or not really, is it all upsides in being able to trivially combine multiple data streams or integrate easily into hubs?

Re: Displayport: A Better Video Interface

#120

Post by dogline » Tue, Jul 11, 2023, 4:55 PM UTC

zerkten wrote: post #95

tivert wrote: post #85

Earlier quoted context omitted.

> If you have multiple screens and a single screen KVM (fairly common) it will do the re-arrangement that you've experienced. With EDID support it keeps both output alive resulting in no re-arrangement. Can you tell me some KVM switches that have a working implementation of that feature? I'm looking for one. I'm still using a DVI KVM, because when I tried to upgrade to Displayport (years ago), I ran into the problem…

I have a TESmart (TES-HDK0402A1U-USBK) from https://www.amazon.com/gp/product/B08259QL5J/ref=ppx_yo_dt_b... which works fine in this regard. This was probably the 4th DisplayPort KVM I tried due to keyboard issues with the others.

I'm looking too, but that one linked has HDMI out only, with DP and HDMI in. Don't you lose the benefit of DP with this setup?