Re: [Bug 220748] usb: xhci_queue_isoc_tx_prepare ignore start_frame and always assumes URB_ISO_ASAP is set

[Michal Pecio <michal.pecio@gmail.com>]

On Thu, 7 May 2026 23:09:18 -0400, Alan Stern wrote:
> On Thu, May 07, 2026 at 11:54:32PM +0200, Michal Pecio wrote:
> > Alan pointed out that kerneldocs are more up to date, but there is
> > still a crucial error there: on ehci-hcd, an URB submitted too late
> > completes with -EXDEV instead of the submission failing with -EXDEV.  
> 
> I don't remember the details exactly, but are you perhaps not taking 
> care to distinguish between URBs that are partially too late (some of 
> their packets' time slots have expired but some have not) and URBs that 
> are entirely too late (all of their packets' time slots are expired)?
> 
> As I recall, the first case is supposed to complete with some of the 
> packet statuses set to -EXDEV, whereas in the second case the entire 
> submission is supposed to fail with -EXDEV.

... which was an artificial distinction requiring drivers to handle
substantially the same problem in two ways. They didn't, therefore

24f531371de1 USB: EHCI: accept very late isochronous URBs

changed it to EXDEV completion in all cases. AFAIK, this code still
stands. I can't find the string "EXDEV" anywhere in ehci-hcd source.
Note: every frame start with this status so in case of missed transfer
the driver simply leaves it unchanged.

Regards,
Michal