AMD Continues Work On USB4 Support In Their Linux Graphics Driver

[phoronix]

Phoronix: AMD Continues Work On USB4 Support In Their Linux Graphics Driver

Earlier this month AMD's open-source driver engineers began posting patches for the AMDGPU kernel driver to handle USB4 DP tunneling. That tunneling for DisplayPort with USB4 is for upcoming Yellow Carp / Rembrandt APUs. The USB4 driver bring-up within AMDGPU continues...

https://www.phoronix.com/scan.php?page=news_item&px=AMDGPU-More-USB4-DC

[linner]

Judging by AMD's previous attempts at USB, I'm not holding my breath.

[brad0]

Judging by AMD's previous attempts at USB, I'm not holding my breath.

I wouldn't be holding my breath for anything USB period.

[cl333r]

I wouldn't be holding my breath for anything USB period.

Why? Is USB bad?

[Quackdoc]

Is there a difference between Tunneling and alt mode? or just a difference in nomenclature? I am assuming there is, because I can't see why it would need software side work if not. as alt mode is literally just dp in to USB controller.

but what is the difference? will this allow AMD GPUs to utilize onboard USB ports via USB protocol bypassing the need for display in, for usb4 cards.

or is this just for APUs in practice, refining the code to play nice with DP to USB controllers?

[WonkoTheSaneUK]

Is it really called USB4 this time?

Or will they change it to USB 3.2 Gen 2.11.13.563.785.786.74856 before release? /s

[tstrunk]

I hope for AMD TB4 support. It's really the only thing missing from their laptops.

[stormcrow]

Why? Is USB bad?

It's been a mismanaged cluster-ef since its inception. It displays the worst attributes of design-by-committee (and the foxes guarding the hen house - the committee is made of "stakeholders" i.e. the companies with tendencies towards proprietary connectors): partially incompatible implementations, race-to-the-bottom designs, 'fix it in the driver', multiple incompatible connectors, multiple completely incompatible standards using the same connector, etc.

The USB driver subsection has a huge list of "quirks" to work around hardware bugs and complete breakage. Historically, AMD and USB have been pretty problematic with breakage in their hardware implementations. I know of one such chipset that was so broken, AMD required main board makers to ship an add-on board so it would have functional USB.

[agd5f]

Is there a difference between Tunneling and alt mode? or just a difference in nomenclature?

Yes they are different. See slides 21, 22, and 36 of this presentation for more details:
https://www.usb.org/sites/default/fi...B%20Type-C.pdf

[Quackdoc]

Yes they are different. See slides 21, 22, and 36 of this presentation for more details:
https://www.usb.org/sites/default/fi...B%20Type-C.pdf

Apologies, I am still a little confused, I was reading the slides from the linked presentation and slides 17 and 27 imply that a display tunneling is a single end to end path, described as a one way logical connection. Now I do have a few guesses as to what it is, but I doubt any of them are accurate. and the one you linked does do quite frankly a poor job at distinguishing the difference, though does make me realize they are two different technologies, My strongest guess as to the difference is as follows,

-USB Alt mode works by assigning a protocol to a lane, (leading to a bunch of crappy USB hubs). My strongest guess is that USB tunneling on the other hand works purely in configuration layer, hence allowing the USB4 routers to dynamically choose what to prioritize (possibly on the fly?).

I realize I am not the smartest man, but this is the only thing I can think of that holds any real possibility, but if this is the case, I don't see why a gpu driver would need to implement support for this, as I would think it would be done purely within USB4, so I doubt that my guess is entirely accurate, or at least missing some critical information. Regardless thanks for the reply, it helped me understand that there is in fact a difference in the two technologies, even if I don't understand what that difference is.

https://www.usb.org/sites/default/files/D1T1-3%20-%20USB4%20System%20Overview.pdf