I know that the presentation of the message is the responsibility of the application (user space), but to do this is necesary an event from usb driver (I think it).
A timeout with no activity at all can do it.. That's Userspace C 101 - select() with a timeout...
To implement a timout first, an event is needed. The standar state "when device is attached...". This is a physical event, so at this time the user space needs an event from kernel space, to know that something should be done (start timout, show message or anything else). The problem is that the only message is "unable to enumerate USB device on port...", but this one can't be trapped frome u/mdev (I thought)
Nowdays when a non responsive device is attached, "unable to enumerate USB device on port... " is logged a in dmesg, but not event is dispatched (by example in usb_uevent). Without an event application should poll the log (loading the system unnecessarily) searching new "not responsive devices".
To comply with the standard usb driver should be modified?
No, because userspace can detect the condition on its own and tell a user about it.
I'm probably confusing responsibilities of user and kernel space. I appreciate your opinion/answer.
Yes, you are. Although I suspect the "standard" you're quoting is confusing them as well....