With the older cable it wouldn't even know what the other side could be capable of.
That's actually untrue because for USB2 vs USB3 my computers already showed notifications that the USB2 cable is slower than necessary. The computer KNOWS the other device, it has a driver for it, and the driver can say "this device is capable of more".
Sometimes yes, other times it might be possible in another way, but a lot of drivers are generic and don't have an exhaustive list of all devices in existence. Devices only need to be identified as a certain (generic) type.
It's still certainly possible for a device to report it's capabilities and plenty of devices seem to correctly do it already.
It would know, the wSpeedsSupported field on the device tells the host which speeds the device is capable of.
but it could at least report the capacity of the cable. that's still useful when you get a badly advertised cable that you thought could do more, or worse, got a fake cable.
This. Apple does something similar if you try to pull too much power
Only in the power case -- how can it know that you didn't intend to use USB 1? It wouldn't be able to tell what the other side is capable of in that case, hence the fallback.
It could know via USB descriptors, and match the device capabilities from the descriptors against what the cable allows.
Re:USB4 Specification
by egypturnash on Wednesday September 04, 2019 @01:27AM
(#20874256)
Does any computer actually do such a thing?
Windows 7 did for USB2 devices plugged into a USB1 port: https://www.makeuseof.com/tag/usb-speederror/
If the computer can identify the device’s capabilities (using some kind of bus command, I’m not very familiar with the USB protocol) separately from speed testing the cable+device combination, no reason why it couldn’t work for USB 2/3/4.
Of course, this approach relies on the device accurately reporting its capabilities, which may not be the case for the more cheap-and-cheerful gadgets.
Windows 8 (and perhaps 10, can't remember) alerted me when I used a USB 3 thumbdrive in a USB 2 port
Re:USB4 Specification
by organsnyder on Wednesday September 04, 2019 @09:28AM
(#20876981)
Windows 10 shows a notification whenever my USB-C portable monitor is using USB video (via the monitor's DisplayLink chip) rather than DisplayPort.
Why would it be silent? The computer would hopefully show a small notification that the transfer is happening slower than it would with a newer cable