Re: [Qemu-devel] [PATCH] ohci: Clear the interrupt counter for erroneous transfers

[Gerd Hoffmann]

On Sun, Jul 29, 2018 at 09:19:28PM +0200, Sebastian Bauer wrote:
> This is mandated by the ohci specification. It tells at 6.4.4 on page 104
> that for transfer descriptors that are retired with an error the done
> queue interrupt counter is cleared as if the interrupt delay field of the
> descriptions were zero.
> 
> Before this change, error conditions were handled similarly to the
> successful condition which is especially troublesome for control transfers.
> Some drivers (e.g., the AmigaOS-one) as well as the example code in the
> spec, set the setup stage with an interrupt delay of seven (which means no
> interrupt). This is fine under normal conditions, because one usually
> doesn't want to be notified about the completion of this stage. However, if
> an error occurs in this stage, these drivers will not get notified with the
> current implementation. The fix addresses this by following the spec more
> closely. Also, otherwise, the ability to set interrupt delay to seven would
> be useless.
> 
> Note that Linux drivers that I looked at don't seem to be affected as they
> set six as the interrupt delay presumably for the reason that they won't
> get notified otherwise.

Added to usb queue.

thanks,
  Gerd