Re: Thunderbolt3/USB4 targeting: should the wiki materials be more explicit about Thunderbolt 3 vs. Thunderbolt 4 distinctions?

Hey Mark!

How are you doing ?

Very glad to see you interested in USB4 and it's related technologies, and
I do notice that you are, just like myself, also generally interested in
USB based on some encounters on mailing lists and Discord.

To help make this discussion thread be more productive and to make sure it
goes in the right direction, allow me to ask a couple of questions before I
respond with any answers or opinions:
- Which wiki materials you are referring to ?
- Would you please share the resources based on which you extracted this
information ? This will allow me, and hopefully others, to review them and
see if we all come to the same conclusions or insights

Looking forward to your reply

On Mon, Jan 20, 2025 at 5:58 AM Mark Millard <marklmi@yahoo.com> wrote:

> Here is my quick attempt at noting distinctions and some possible
> handling points. It is possible that protocols make some of this
> more automatic/clear than I presume. (I would not know.)
>
>
> Overall: Is it a goal to have a Thunderbolt 4 capable PC be able to
> operate as a Thunderbolt 3 PC when booted by FreeBSD? That would be
> different then just allowing FreeBSD to reject such a PC or to end
> up without even Thunderbolt 3 support for such a PC.
>
> I'm not claiming that "converting a Thunderbolt 4 capable PC into
> a Thunderbolt 3 PC instead" should be avoided: It should be explicitly
> documented if targeted and, if not targeted, the alternative should
> instead be explicitly documented. It might be too early to say yet for
> some of the example issues. (I view this more issue by issue
> contributions to the overall status than just the final overall status.
> Different issues might go different directions.)
>
>
> Ports per accessory:
>
> Thunderbolt 3: Allow configuring up to 2 ports (so: daisy chain only by
> accessories)
> Thunderbolt 4: Allow configuring up to 4 ports (so: star is possible)
>
> So:       No support for star (3 or 4 ports used)?
> Possibly: Only support devices with 1 or 2 ports?
> But:      What about 2 used of 3 or 4 present?
> Note: Mixes with hot plugging!
>
> So:   Lack of SW support could turn a PC capable of Thunderbolt 4
>        into a Thunderbolt 3 PC?
>
>
> Minimum PCIe bandwidth (minimums):
>
> Thunderbolt 3: Must support 16 Gbps or more
> Thunderbolt 4: Must support 32 Gbps or more
>
> Not so sure that this aspect makes a difference.
>
>
> Monitors (minimums):
>
> Thunderbolt 3: No 8K monitor support but 1 5K monitor optionally supported
> Thunderbolt 4: Allow configuring for 2 4K monitors or 1 8K monitor
> Note: Some Thunderbolt 3 implementations can support 2 4K monitors
> Note: USB4 apparently does not specify a minimum nK-ish figure.
> Note: Looks like frequency for Dual Full HD is another difference
>
> So: Do not support 8K monitors? (What of 2 4K monitors?)
>
> So: Do not support the higher Dual Full HD frequency?
>
> So: Lack of SW support could turn a PC capable of Thunderbolt 4
>      into a Thunderbolt 3 PC?
>
>
> Power (minimum for most ports):
>
> Thunderbolt 3: At least 15W
> Thunderbolt 4: At least 15W
> Note: USB4: At least 7.5W
>
> Not so sure that this aspect makes a difference.
>
>
> At least Power port for PC charging for thin and light notebooks that
> require < 100W to charge:
>
> Thunderbolt 3: No requirement
> Thunderbolt 4: At least one such port on the notebook
>
> So: Lack of SW support could turn such a notebook capable of Thunderbolt 4
>      into a Thunderbolt 3 notebook?
>
>
> Wake from Sleep Mode:
>
> Thunderbolt 3: Optionally keyboard/mouse input to wake a sleeping computer
> Thunderbolt 4: Required keyboard/mouse input to wake a sleeping computer
>
> So: Do not support keyboard and mouse input waking a sleeping computer?
>      (Lack of SW support could turn a PC capable of Thunderbolt 4 into
>      a Thunderbolt 3 PC?)
>
>
> Compatibility:
>
> Thunderbolt 3: Need not be compatible with some Thunderbolt 4 specific
> requirements
> Thunderbolt 4: Required to be compatible with Thunderbolt 3
> devices/requirements
>
> So: Various examples of SW potentially turning a Thunderbolt 4 capable PC
>      into a Thunderbolt 3 PC
>
>
> Security:
>
> Thunderbolt 3: Allows optional VT-D based DMA or equivalent
> Thunderbolt 4: Required to support VT-D based DMA or equivalent
>
> So: Is there to be support for uses "VT-D based DMA or equivalent"?
> Or: Is this an example of SW converting a Thunderbolt 4 capable PC
>      into a Thunderbolt 3 PC instead?
>
> USB4 Specification Status:
>
> Thunderbolt 3: Compatible
> Thunderbolt 4: Compliant
> (I've seen references to such a distinction but do not well understand the
> specifics.)
>
>
> ===
> Mark Millard
> marklmi at yahoo.com
>
>
>
-- 
Thanks
- Mohammad Noureldin
--
"Life is like riding a bicycle. To keep your balance you must keep moving"
- Albert Einstein