USB-C how to check if it has HDMI signal?

Xwang · 2021-08-31 12:06:52

Hi to all,
I've an Asus N752VX which has both usb-c port and hdmi output.
I've seen that there are some usb-c hubs which have hdmi and LAN port.
If I find one which is compatible with linux, is it enough to have a second hdmi outport or should I check previously if the usb-c port contains the hdmi signal?
On an asus help page there is an explanation of usb ports symbols according to which my laptop usb-c port does not have a video signal.
However I'm not sure if that page is for my laptop tooo and, moreover, I've not understood if it is a software (Windows) limitation or an hardware one.
Is there any way in linux to understand if an usb-c port outputs a video signal?

Last edited by Xwang (2021-08-31 12:07:08)

Lone_Wolf · 2021-08-31 13:23:02

Usb-c has optional alternate modes which allow displayport , hdmi and such options .
Support for those modes needs to be provided by the hardware.

Complicating things is that Thunderbolt3 uses the same connector and has support for DisplayPort screens .

No idea how to check for usb-c alternate modes, but the thunderbolt controller has its own kernel module.

$ lsmod | grep bolt

should clarify if your laptop has thunderbolt connections.

Xwang · 2021-08-31 13:35:59

Lone_Wolf wrote:

Usb-c has optional alternate modes which allow displayport , hdmi and such options .
Support for those modes needs to be provided by the hardware.
Complicating things is that Thunderbolt3 uses the same connector and has support for DisplayPort screens .
No idea how to check for usb-c alternate modes, but the thunderbolt controller has its own kernel module.
$ lsmod | grep bolt
should clarify if your laptop has thunderbolt connections.

Thank you,
without anything connected to the port I've tried to give that command. Since it returned nothing, I think that the laptop doesn't have thunderbird connections.
Regarding usb I'll continue to investigate about the alternate modes.

progandy · 2021-08-31 13:38:34

I think there should be some indication in /sys/class/typec, but that may only show if something is plugged in.

Xwang · 2021-08-31 13:49:16

progandy wrote:

I think there should be some indication in /sys/class/typec, but that may only show if something is plugged in.

I've tried to connect a usb hub to the usb-c port, but there is no /sys/class/typec folder of file.

solskog · 2021-08-31 14:13:13

If you are referring to a USB-C to HDMI adapter, Yes it works. I use one myself with archlinux. I think the necessary hardware is the adapter itself.

progandy · 2021-08-31 15:04:50

solskog wrote:

If you are referring to a USB-C to HDMI adapter, Yes it works. I use one myself with archlinux. I think the necessary hardware is the adapter itself.

A good adapter needs a USB-C port that provides a displayport alternate mode.

There are "displaylink" adapters that do not need that, but those do not work well on linux, sometimes only delivering 1 frame per second or not working at all.

Xwang · 2021-08-31 15:40:27

solskog wrote:

If you are referring to a USB-C to HDMI adapter, Yes it works. I use one myself with archlinux. I think the necessary hardware is the adapter itself.

Could you tell me which one are you using, please?
I've seen some of those usb-c hubs with hdmi and lan ports (sometimes also SD card readers) which advertise compatibility with windows/mac/linux/chromeOS but do not say anything about the fact that usb-c port must have specific capabilities.

Last edited by Xwang (2021-08-31 15:45:21)

solskog · 2021-08-31 16:00:47

Lone_Wolf wrote:

A good adapter needs a USB-C port that provides a displayport alternate mode.

I agree! and an HDMI alternate mode in my case.

https://www.ugreen.com/products/9-in-1- … th-4k-hdmi
Widely compatible
It is an ideal USB-C expansion hub for Apple MacBook, Apple MacBook Air, Apple MacBook Pro, Apple iMac / iMac Pro (21.5 inches, 27 inches), Google ChromeBook Pixel, Dell, as US, HP, Lenovo, and many other Type C laptops. Supported systems drive free for Windows 10/8.1/8/7/XP; linux; MAC OS; IOS; Android.

Available on amazon.com a while ago, maybe not now anymore, but you may find a replacement.

Xwang · 2021-08-31 16:23:06

solskog wrote:

Lone_Wolf wrote:
A good adapter needs a USB-C port that provides a displayport alternate mode.
I agree! and an HDMI alternate mode in my case.
https://www.ugreen.com/products/9-in-1- … th-4k-hdmi
Widely compatible
It is an ideal USB-C expansion hub for Apple MacBook, Apple MacBook Air, Apple MacBook Pro, Apple iMac / iMac Pro (21.5 inches, 27 inches), Google ChromeBook Pixel, Dell, as US, HP, Lenovo, and many other Type C laptops. Supported systems drive free for Windows 10/8.1/8/7/XP; linux; MAC OS; IOS; Android.
Available on amazon.com a while ago, maybe not now anymore, but you may find a replacement.

So your usb-c has hdmi alternate mode, right?
As far as I have understood, mine doesn not have it.
So in case I buy the same, the hdmi port would be dead on my pc, right?

I wanted to have such a device so that to be able to disconnect all cables by just unplugging the usb-c. Moreover with time the HDMI port of the laptop starts to misbehave with false contacts.

progandy · 2021-08-31 17:01:22

As far as I have understood, mine doesn not have it.

If you are lucky, asus just forgot to add the displayport icon on your model. I found one document that claims some N752VX models have it: https://www.steg-electronics.ch/api/Pro … t/1630751/

So your usb-c has hdmi alternate mode, right?

Maybe. Most hdmi adapters identify as DP and use the DP altmode. The HDMI altmode is rare.

Last edited by progandy (2021-08-31 17:07:43)

solskog · 2021-08-31 22:49:10

progandy wrote:

Maybe. Most hdmi adapters identify as DP and use the DP altmode. The HDMI altmode is rare.

At a closer look, my laptop usb-c port does have an (ss->D) symbol on it. As for the alternate mode, after I read the wiki:
https://en.wikipedia.org/wiki/DisplayPo … ode_(DP++)
I wondering if the usb-c port with displayport alternate mode support DP++? Means it requires an active HDMI adapter?

Xwang wrote:

I wanted to have such a device so that to be able to disconnect all cables by just unplugging the usb-c. Moreover with time the HDMI port of the laptop starts to misbehave with false contacts.

me as well, same reason for purchasing this adapter.

Last edited by solskog (2021-08-31 23:49:16)

Xwang · 2021-09-01 06:38:47

progandy wrote:

As far as I have understood, mine doesn not have it.
If you are lucky, asus just forgot to add the displayport icon on your model. I found one document that claims some N752VX models have it: https://www.steg-electronics.ch/api/Pro … t/1630751/
So your usb-c has hdmi alternate mode, right?
Maybe. Most hdmi adapters identify as DP and use the DP altmode. The HDMI altmode is rare.

Mine is NV752VX-GC132T which is not listed there and the only symbol near the usb-c port id the SS one.
Moreover the user manual does not report anything about hdmi or DP capability odf the usb-c port.

solskog wrote:

progandy wrote:
Maybe. Most hdmi adapters identify as DP and use the DP altmode. The HDMI altmode is rare.
At a closer look, my laptop usb-c port does have an (ss->D) symbol on it. As for the alternate mode, after I read the wiki:
https://en.wikipedia.org/wiki/DisplayPo … ode_(DP++)
I wondering if the usb-c port with displayport alternate mode support DP++? Means it requires an active HDMI adapter?
Xwang wrote:
I wanted to have such a device so that to be able to disconnect all cables by just unplugging the usb-c. Moreover with time the HDMI port of the laptop starts to misbehave with false contacts.
me as well, same reason for purchasing this adapter.

In my case it seems that the usb-c port does not have any alt mode and since it seems to be an hardware configuration, I expect that there should be some way in which the hardware communicate to the operating system this capability.
Just to avoid buying something which does not work.

Arch Linux

#1 2021-08-31 12:06:52

USB-C how to check if it has HDMI signal?

#2 2021-08-31 13:23:02

Re: USB-C how to check if it has HDMI signal?

#3 2021-08-31 13:35:59

Re: USB-C how to check if it has HDMI signal?

#4 2021-08-31 13:38:34

Re: USB-C how to check if it has HDMI signal?

#5 2021-08-31 13:49:16

Re: USB-C how to check if it has HDMI signal?

#6 2021-08-31 14:13:13

Re: USB-C how to check if it has HDMI signal?

#7 2021-08-31 15:04:50

Re: USB-C how to check if it has HDMI signal?

#8 2021-08-31 15:40:27

Re: USB-C how to check if it has HDMI signal?

#9 2021-08-31 16:00:47

Re: USB-C how to check if it has HDMI signal?

#10 2021-08-31 16:23:06

Re: USB-C how to check if it has HDMI signal?

#11 2021-08-31 17:01:22

Re: USB-C how to check if it has HDMI signal?

#12 2021-08-31 22:49:10

Re: USB-C how to check if it has HDMI signal?

#13 2021-09-01 06:38:47

Re: USB-C how to check if it has HDMI signal?

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