[GTALUG] USB-C/3.1 Video and Linux

[Russell]

On March 24, 2018 9:53:59 AM EDT, Russell Reiter <rreiter91 at gmail.com> wrote:
>On 24 March 2018 at 08:08, Giles Orr via talk <talk at gtalug.org> wrote:
>> On 23 March 2018 at 20:01, Scott Sullivan via talk <talk at gtalug.org>
>wrote:
>>>
>>> On 2018-03-23 12:50 PM, Giles Orr via talk wrote:
>>>>
>>>> A couple days ago I got a Best Buy flyer, and they have this item:
>>>>
>>>>
>>>>
>https://www.bestbuy.ca/en-ca/product/asus-zenscreen-15-6-fhd-60hz-5ms-gtg-ips-lcd-monitor-mb16ac-dark-grey/10737845.aspx
>>>>
><https://www.bestbuy.ca/en-ca/product/asus-zenscreen-15-6-fhd-60hz-5ms-gtg-ips-lcd-monitor-mb16ac-dark-grey/10737845.aspx>?
>>>>
>>>> It's a portable IPS LCD screen from Asus.  I have a similar item
>from
>>>> about three years ago that has two connectors, one for USB
>power-only and
>>>> the other for VGA/HDMI.  There were other models at the time that
>used only
>>>> one connector, USB for both data and power - but that required a
>driver (and
>>>> would have been painfully slow if it was USB2).
>>>>
>>>> But now here's this new model: it's one connector only, USB-C.  And
>>>> presumably USB3.1.  And USB3.1 can carry video.  But at this point
>I get
>>>> lost among the standards and their implementations and which one
>supports
>>>> what.  I have an Asus Zenbook (it's Linux-only at this point) that
>has a
>>>> USB-C connector, but I suspect it's USB3.0.  So the first question
>is: how
>>>> do I check that?  Second, does Linux support video-over-USB3.1?  Do
>I need a
>>>> special cable?  Is this "Thunderbolt?"  How can I check if my
>machine would
>>>> support this?
>>>
>>>
>>> The Spec you linked say it's DisplayLink, which is the software
>based
>>> video solution that requires a driver.
>>>
>>> https://en.wikipedia.org/wiki/DisplayLink
>>>
>>> USB-C is only a specification for a cable and connector, and
>somewhat
>>> agnostic about the data communications spec used across it. The
>cables are
>>> of high enough quality that they can support multiple data
>communications
>>> specs, generally referred to as alt-modes.
>>>
>>>
>https://en.wikipedia.org/wiki/USB-C#Alternate_Mode_partner_specifications
>>>
>>> Thunderbolt 3 for example co-oped the USB-C cable spec for it's
>cables,
>>> much like in the previous generations it co-oped the
>mini-displayport cable
>>> spec.
>>>
>>> Intel makes a point that a port carrying Thunderbolt 3 should also
>be
>>> cross wired with USB 3.X and Display Port hardware to output those
>signals
>>> as well.
>>>
>>> So if you want a monitor that uses a Type-C connector, your looking
>for a
>>> display-port monitor. Which your not likely to find in the portable
>market
>>> yet.
>>>
>>
>> Now that I knew what to look for, re-examination of the text and
>pictures
>> shows a couple interesting things: "USB Type-C connectivity with
>hybrid
>> signal solution for Type-C and Type-A source compatibility (requires
>a
>> DisplayLink driver for Type-A connection)."  So it's implying that it
>> doesn't need a driver for Type-C.  And looking at the pictures,
>there's a
>> "DisplayPort" icon next to one of the buttons on the front.  So ...
>>
>> My other questions stand:
>>
>> - how can I figure out what USB protocol (3.0 or 3.1) the type-C
>connector
>> on my Linux computer supports?
>
>lspci -d ::0c03 -k  will display the vendors controller and kernel
>driver in use.
>
>> - (clearer understanding leads to a clearer question here, although
>I'm
>> still not sure I'm saying it right) does Linux support DisplayPort
>video
>> over USB-C?

Oops. No usb-c display context for this monitor. This test used the display link binary and a USB 2 adapter on Ubuntu LTS.  

https://www.phoronix.com/scan.php?page=article&item=asus-mb16ac-zenscreen&num=2

>
>I think the short answer is yes. If you can hard wire a DisplayPort to
>HDMI adapter
>cable you must surely be able to sink to the host connections logically
>as well.
>
>Has somebody done this yet, I don't know.
>
>Since kernel 4.12 there has been development on a state machine for
>hosting sinks.
>
>https://www.phoronix.com/scan.php?page=news_item&px=USB-Type-C-Promotion-Linux-4.15
>
>Power management and signalling are all represented, soft-jacking is
>another issue.
>
>https://superuser.com/questions/1192638/whats-up-with-hdmi-and-displayport-over-usb-c
>
>*Alternate mode data*
>
>https://github.com/torvalds/linux/blob/master/drivers/usb/typec/tcpm.c
>
>HTH
>>
>> --
>> Giles
>> https://www.gilesorr.com/
>> gilesorr at gmail.com
>>
>> ---
>> Talk Mailing List
>> talk at gtalug.org
>> https://gtalug.org/mailman/listinfo/talk
>>

-- 
Russell