Vostro 5590: Why no Intel Display Audio support for DisplayPort over USB-C

@cramcram  I'm looking at Computer Management and I'm not seeing an "Audio Inputs and Outputs" section, but those types of devices can also be shown under Control Panel > Sound and Device Manager. If they're grayed out wherever you're looking at them, then based on the fact that you said you don't have anything connected, it's likely because Windows grays out audio devices that aren't currently in a usable state, and Intel Audio-based output devices wouldn't be usable when nothing is connected to the outputs that the Intel GPU controls, namely the HDMI and USB-C/DisplayPort outputs.  You would likely find that if you DID connect your system to a device that could receive audio over HDMI or DisplayPort, such as a TV or AV receiver, at least one of those devices would no longer be grayed out.

As for the claim that the Vostro 5590 supports DisplayPort over USB-C without audio, I'm not sure what you're basing that on.  Did you read something somewhere?  Or did you just infer that based on seeing grayed out devices while you didn't have anything connected to the system?  I've successfully transmitted audio using USB-C to DP and USB-C to HDMI cables while they were connected to systems controlled by Intel GPUs, and the presence of Intel Audio devices in your system (even if currently inactive) suggests that your system would support that too.  Of course not all displays you might connect to the system support receiving audio over their HDMI/DP inputs, but that wouldn't be the system's fault.

Just curious as what is the maximum resolution and refresh rate you can get over the USB-C Displayport?

@markmike  when using a USB-C to DP cable, you'd have a full DisplayPort 1.2 interface available, which would support 4K 60 Hz as well as some ultrawide resolutions -- and you would also be able to run multiple simultaneous independent displays via DisplayPort daisy chaining or an MST hub so long as the total bandwidth requirements of your displays didn't exceed the bandwidth available over a DisplayPort 1.2 interface.  But for single displays, basically if the display can be driven at its maximum resolution over a regular DisplayPort connection, then the overwhelming likelihood is that it only requires DisplayPort 1.2 and therefore will run normally via a USB-C to DP cable.  There are very few displays on the market that require something more "exotic" like DisplayPort 1.3 or better, or Thunderbolt 3, or dual DisplayPort connections.  But if you're curious, such displays would include LG's UltraFine 5K resolution display (5120x2880, requires Thunderbolt 3) and Dell's 8K display (7680x4320, requires two DisplayPort 1.4 connections to run at 60 Hz).  Short of that, even ultrawide displays like Dell's U4919DW (5120x1440) can run over regular old DisplayPort 1.2.

There are also a very small handful of systems that can support DisplayPort 1.4 over USB-C.  If you have one of those and a USB-C to DP cable that specifically supports DisplayPort 1.4 (these are quite rare right now), then you can support even higher-end display setups.  Precisely how high you can go is less clear because DisplayPort 1.4 can optionally include support for DisplayPort DSC (Display Stream Compression), and if THAT is supported, then you can go a LOT higher.  But even if the system doesn't support DSC, a DP 1.4 interface has enough bandwidth to run a 5K display (if it offers a DisplayPort 1.3 or higher input rather than only accepting TB3) or dual 4K 60 Hz displays.

@markmike  one minor note to add to what I wrote above.  The answer I gave assumes that you are using all four high speed lanes in a USB-C cable for DisplayPort, as would be the case when using a USB-C to DP cable.  If on the other hand you're connecting to a USB-C device that configures the link to support video and USB 3.x data simultaneously, then USB 3.x requires two lanes, which means DisplayPort bandwidth gets cut in half.  Most USB-C (non-Thunderbolt) docking stations set up the USB-C link this way.  Some USB-C displays also work this way if they have USB 3.x ports built into them, although some recent Dell USB-C displays offer an option within the display settings to allow you to choose how you want the display to set up the USB-C link.  You can have it run video over all four lanes and then only have USB 2.0 data speeds available (USB 2.0 runs over dedicated pins within a USB-C connector), or have it run two lanes each of video and USB 3.x.  This flexibility comes in handy because there are certain single display setups (and daisy chain setups that might begin with a USB-C display) where a system that supports DisplayPort 1.4 over USB-C would be able to run the display setup as normal over two lanes, i.e. with two lanes left over for USB 3.x data, while a DisplayPort 1.2 over USB-C system would have to use all four lanes for video to run that display setup.  So if a user had a DP 1.2 system and was fine with only USB 2.0 because they only had basic peripherals plugged into the display's USB ports (or they weren't using them at all), they can optimize for video bandwidth as much as possible.  Meanwhile, a user with a DP 1.4 system would still be able to run the same display setup with the added benefit of running USB 3.x as well.

And then in terms of maximum refresh rate, again as long as the combination of resolution and refresh rate fits within a DisplayPort 1.2 link, you'd be able to run it over USB-C -- as long as there weren't GPU limitations involved.  I know Intel GPUs can go up to at least 120 Hz, but I don't know if they can go higher than that regardless of resolution.  I just haven't tested it.

@cramcram  glad it's fixed, although I'm not sure why you had to switch to a different audio device to get the Intel Audio devices to even appear.  Sounds like a bug in some driver to me.  I wouldn't expect BIOS enumeration to be the issue here given that Intel Audio devices will come and go during the same Windows session as you connect and disconnect display devices that can receive audio -- or at least that's how it's supposed to work.  When I dock and undock my own system, I can see audio devices for my displays come and go as normal without any reboots.  But as long as it's working now, I guess!

I found out that the intel audio device will disappear if you shutdown the laptop with the Realtek speakers selected as the default output device.  On the next boot, the intel device is missing, even from the device manager.  To fix you have to choose something else as the default output device (like say, the headphones) and reboot.  When it comes back up the intel device re-appears as a choice.

Not sure if it is the BIOS or the device drivers (or both) but it is a very repeatable bug.