USB-C, Thunderbolt 3, and HDCP

HDCP isn't an issue with USB-C/Thunderbolt itself, since there are a variety of USB-C to HDMI cables that claim support for HDCP.  I don't think they need to do anything special to achieve that; they just list it for marketing and customer reassurance.  However, docks may or may not implement support for passing it through.  The two primary USB-C and Thunderbolt docks from Dell are the WD15 and TB16, respectively.  I just Googled "Dell WD15 HDCP" and "Dell TB16 HDCP", and in each case the top hit was their respective FAQ pages here and here.  Both of them note that they don't support HDCP.  The only other dock that might work with those systems is the D6000, but it uses a DisplayLink chipset as well, and I would recommend against it on that basis alone, especially if you plan to watch movies and such on the attached displays.  You may want to look at third-party USB-C and TB3 docks, although I'm noticing that even some of those specifically claim no HDCP support.  I wouldn't have expected that, but maybe nobody wants to pay the licensing fees for HDCP.  Even more strangely, I'm seeing other forums posts indicating that people can watch Netflix on displays attached via the WD15 and TB16 just fine.  Maybe the docks support an older version of HDCP that's enough for Netflix and simply don't support newer versions required by things like Ultra HD Blu-ray discs?  Then there's this thread on the DisplayLink forums indicating that some DisplayLink setups work fine with HDCP and also noting that Netflix will simply lower its video quality rather than completely refusing to play if HDCP requirements aren't satisfied.

Also note that if you want to be able to CHARGE your system through a dock, Dell docks are your only option if you want an XPS 15, because the XPS 15 requires 130W for proper functionality, which is more than the USB Power Delivery spec's official 100W max.  To charge an XPS 15 through a dock, you need a WD15 with a 180W adapter or a TB16 with a 240W adapter.  Both of those docks are also available with lower wattage adapters, which you would NOT want with an XPS 15.  As for the Inspiron 15 7000, I'm not sure about the system you're talking about since "Inspiron 15 7000" isn't a specific model -- nor is XPS 15 for that matter, but all XPS 15s with USB-C/TB3 connectors use 130W power sources.  But both of those names are essentially product lines that include a variety of models that have been introduced over several years.  That's a bit like saying, "I'm looking at a BMW 3 Series" -- ok, but that doesn't describe a specific model.

Finally, note that not all systems with a USB-C port support using it for display output.  That is a capability called DisplayPort Alt Mode, and it is an optional component of the USB-C spec, just like being able to charge the system via USB-C.  There are some laptops whose USB-C port is simply another USB data port that supports USB data traffic, usually at 3.1 Gen 2 speeds rather than 3.1 Gen 1 speeds, but technically even that's optional.  The XPS 15 models definitely support display output via USB-C/TB3.  I'm not sure about the Inspiron system.  You'd be able to run dual 1080p displays with regular USB-C even through a dock, no need for TB3. I wrote a detailed post about how USB-C and TB3 work, including the different display capabilities depending on what equipment you're using here if you're interested.

Thanks, that was very helpful. I had looked at the product pages for those docks and there was no mention of HDCP but hadn't looked at their knowledge base entries.

 The Inspiron I'm most interested in is 7586. The product page states it has a USB-C port with DP and power delivery. If I understand correctly, this means I should be able to connect two 1080p external displays through this single port (via a dock), but whether there is a dock that will enable me to pass HDCP content is uncertain. Ideally, I would like to use a dock but if that doesn't work and I understand correctly I should be able to achieve a dual external monitor setup without HDCP issues by connecting one display to the USB-C port (with an adapter instead of a dock) and my other display through the HDMI port. Is that correct?

My two external monitors are both Dell U2312HM. These are 1920x1080 panels with VGA, DVI, and DisplayPort input options.

If I go for XPS 15 its likely to be a used/refurbished 9550 or 9560 as my budget probably won’t stretch to 9570 or 9575.

Thanks

Yes, based on the USB-C port description for that system, it supports display output, and therefore yes, if you use a USB-C to DisplayPort cable for one display and a regular HDMI cable for the other, you can run two displays and not have to worry about HDCP issues. If the displays support DisplayPort daisy chaining, you could connect both displays through a single connection to your system by using the DisplayPort OUTPUT on Display #1 to feed the DisplayPort input on Display #2. Good luck!

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@jphughan wrote:

If the displays support DisplayPort daisy chaining, you could connect both displays through a single connection to your system by using the DisplayPort OUTPUT on Display #1 to feed the DisplayPort input on Display #2. Good luck!

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If DisplayPort Alt mode is present and the laptop supports multiple external displays, does it necessarily also mean it will support DisplayPort chaining (MST)?

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@osm wrote:

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@jphughan wrote:

If the displays support DisplayPort daisy chaining, you could connect both displays through a single connection to your system by using the DisplayPort OUTPUT on Display #1 to feed the DisplayPort input on Display #2. Good luck!

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If DisplayPort Alt mode is present and the laptop supports multiple external displays, does it necessarily also mean it will support DisplayPort chaining (MST)?

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DisplayPort Alt Mode just refers to sending DisplayPort (any version of it) over a USB-C connector. DisplayPort MST is part of the DisplayPort 1.2 spec, but it’s an optional component. Multi-display support definitely does not imply MST support since multi-display support existed long before MST. All that said, Intel GPUs for the last several years have supported DisplayPort MST, and most laptops have their display outputs physically wired to the Intel GPU even if the laptop also has a discrete GPU. So MST support on a system recent enough to have USB-C with DP Alt Mode is a very safe bet. However, if you use a dock, some of the dock’s own outputs may not support MST, even if the dock supports receiving an MST signal from the system to feed those outputs. For example, the WD15 dock’s mDP out supports MST, so you can daisy chain displays off that one output (I do this at home), but the TB16’s DP and mDP outputs do not support MST.

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@jphughan wrote:

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All that said, Intel GPUs for the last several years have supported DisplayPort MST, and most laptops have their display outputs physically wired to the Intel GPU even if the laptop also has a discrete GPU. So MST support on a system recent enough to have USB-C with DP Alt Mode is a very safe bet.  

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Thank you once again.

Can I assume from what you have written that if the Intel GPU is wired to the display outputs, whether or not the discrete GPU supports MST is irrelevant?

Is there a resource I can look at online to determine which GPU is wired to the display outputs on Dell systems? I am still interested in the Inspiron 7586, but there are a few other Dell systems I am also interested in so would be useful for me to know were I can look this up myself.

If display outputs are wired to the Intel GPU does it mean the discrete GPU can only be used when no external display is attached?

However, if you use a dock, some of the dock’s own outputs may not support MST, even if the dock supports receiving an MST signal from the system to feed those outputs. For example, the WD15 dock’s mDP out supports MST, so you can daisy chain displays off that one output (I do this at home), but the TB16’s DP and mDP outputs do not support MST.

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Thanks, that's useful to know.

Do you know if these docks are using (or are able to use) MST internally? 

i.e. take a single DisplayPort channel on the input and split to the two display outputs from the dock using MST, or do they require two DisplayPort channels on the input to drive the two outputs?