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Daisy Chained monitors not extending
Hi there,
I have 2 monitors daisy chained, however I'm not able to extend them.
I have the following setup:
- Dell XPS 13 9370
- Dell Thunderbolt Dock TB16
- 2 monitors Dell P2719H
- 1 monitor Dell U2715H
The connections:
- Dock connected to laptop's Thunderbolt USB-C (on the left side of the laptop)
- 1 monitor P2719H connected through HDMI to the dock
- 1 monitor U2715H connected through DP to the dock (Dock miniDP output -> monitor DP input)
- 1 monitor P2719H connected through DP to the U2715H monitor (U2715H DP out -> P2719H DP in)
To note that: my monitor U2715H has the setting Display > DP 1.2 DISABLED (see image below) and as well I had to lower the resolution to 1920x1080 for everything to work on.
I don't know what am I missing, but I would like to have the daisy chained monitors extended, but I'm not able to do so.
Maybe, my setup is not even correct?! In the end, how do I connect the 3 monitors in extend mode?
Thanks in advance for your help!
jphughan
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April 29th, 2020 12:00
@Ricardo Saraiva it's been a while, but I seem to remember reading a note in a bit of documentation somewhere that the TB16 itself does not support DisplayPort MST (daisy chaining) on its DisplayPort and Mini-DisplayPort outputs. When you don't have MST support, you get mirrored output on daisy chained displays because the system doesn't see them as independent displays.
Connect the third display to the TB16's DisplayPort output instead, since you seem not to be using that at the moment, and you should be good to go. Note that in order to run 3 external displays, you will first have to disable the built-in display because the Intel GPU in that system only supports 3 simultaneous independent displays total.
jphughan
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April 29th, 2020 13:00
@Ricardo Saraiva There is a way to have more than 3 displays that I'll get to in a moment. But the "official limit" does indeed come from the Intel GPU itself. As of this writing, there are no Intel GPUs that support more than 3 simultaneous independent displays. The TB16 itself can run four displays if the system supports it, but that requires a system that has a discrete GPU that has direct control of the TB3 port, which is fairly rare even among systems that have discrete GPUs in the first place.
The way around the limitation is to use a dock or adapter that uses "indirect display" technology such as DisplayLink. This works because indirect displays are not driven directly by the GPU, so they don't count toward the GPU's maximum number of displays -- but read to the end of this so you know what you're getting into. Given that you already have a TB16, if you just want one more display, the simplest solution would be to get an adapter just for that one extra display. Plugable is a company known for solid products and they make a variety of these adapters, such as this one if you want a DisplayPort output up to 4K 60 Hz, this one if you want HDMI up to 1440p, or this one if you want HDMI up to 4K 60 Hz. You'd just download and install the DisplayLink software, plug one of those into a USB 3.0 port on the TB16, or your system, or some other USB 3.0 hub, and you're good to go. Technically you can use even more of these; I think DisplayLink says they've tested up to 10 displays if I'm not mistaken.
Alternatively, there are whole docks that use DisplayLink. The Dell D6000 is one such dock, and it can run dual displays up to 4K 60 Hz each plus a 4K 30 Hz display. When it's using 3 displays, whichever display is connected to the HDMI output is driven natively by the GPU, but the other two displays use DisplayLink and therefore don't count toward the GPU's maximum.
The catch here is that while the way DisplayLink works allows it to sidestep these GPU limitations, it also comes with some drawbacks that can be significant in certain use cases. I wrote about those drawbacks in the post marked as the answer in this thread. Those issues might not apply to you, or you might decide that it's worth dealing with that issue on one DisplayLink-driven display if the alternative is not being able to run the extra display at all, but just know what you're getting into here. For general productivity use, DisplayLink should be completely fine, but you might have issues if you try to run full screen video on that display, and I definitely wouldn't recommend gaming.
Hopefully this helps!
Ricardo Saraiva
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April 29th, 2020 12:00
If that's the case, I'm not able to have built-in + 3 external displays. Is there any dock that would allow me to do that? Or is this a limitation of my laptop's GPU itself?
Thanks for your answer, BTW.
jphughan
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April 29th, 2020 13:00
@Ricardo Saraiva one somewhat related item I wanted to call out. Be sure you actually WANT to run external displays and the built-in display simultaneously. The reason I say that is because regardless of whether your XPS 13 has the FHD or 4K display, chances are it has some amount of display scaling enabled, i.e. some value above 100%, because even FHD is fairly high pixel density on a 13" display, and 4K is extremely high. By comparison, chances are that on your external displays, you'd be fine with standard 100% scaling. The problem that arises is that while Windows supports running multiple scale factors simultaneously, it does not support optimizing its rendering for multiple scale factors simultaneously. Basically what happens is that when you first log in to Windows, it looks at the scale factor selected for the display that is primary at that time, and it uses that for your entire Windows session. For any other scale factors in use on other displays, or even if the scale factor of the primary display changes, it will continue rendering at that originally selected scale factor and then use GPU scaling to blow up or shrink down the post-render content to suit the other scale factors -- similar to shrinking or blowing up a photo. As you might imagine, this doesn't look as good as actually rendering content for the target scale factor in the first place. The difference is especially noticeable on text, because text is vector-based and therefore can scale virtually infinitely with zero loss of quality as long as you do it pre-render -- but if you essentially render it to an image at one size and then scale it up or down post-render, it won't look as good.
The end result is that when you have displays with multiple scale factors in use simultaneously, you won't be able to have all of your displays looking their best at the same time. Even more annoyingly, remember that I said that Windows chooses its rendering scale factor based on the display that was primary when the user logged in. This means that if the primary display changes in the middle of the Windows session, even the primary display won't look as good as it could, nor will any other display that uses the same scale factor. So for example, let's say you log in while undocked and then connect to your dock where you use an external display as primary, or you log in while docked and then later undock so that you're only using the built-in display. In that case, the "new" primary display won't look as good as it could, and it won't START looking as good as it could until you completely sign out of Windows and sign back in. Locking/unlocking your workstation or just putting your system to sleep won't be good enough.
If you're thinking that this issue would create a huge annoyance for business users who might dock and undock their system several times every day, you'd be absolutely correct. They have to choose between either logging off and back on every time they dock or undock -- which means closing all of their applications -- or else accept that they'll have suboptimal image quality during part of their day.
This is why I tend to recommend that people not try to use displays with very different pixel densities simultaneously, e.g. a laptop built-in display and external displays, or a 24" 1080p display and a 24" 4K display.
Ricardo Saraiva
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April 29th, 2020 16:00
@jphughan thanks for all that useful inputs. That's really good material to help me make a decision.
My setup is for office use (business); for games I prefer my Nintendo Switch.
For now I'll go on with less one display, but I'll study the purchase of that DisplayLink plug.
Thanks a lot! #StaySafe
Happy Donkey
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May 20th, 2021 22:00