Adding Sarah to CC, I just noticed she was the one who added this code.
> -----Original Message-----
> From: Paul Zimmerman
> Sent: Friday, September 09, 2011 1:16 PM
> To: alan stern
> Cc: 'linux-usb@xxxxxxxxxxxxxxx'
> Subject: EHCI isoc scheduling
>
> Hi Alan,
>
> Can you give me a clue about this code in ehci-sched.c/iso_stream_schedule()?
>
> /* For high speed devices, allow scheduling within the
> * isochronous scheduling threshold. For full speed devices
> * and Intel PCI-based controllers, don't (work around for
> * Intel ICH9 bug).
> */
> if (!stream->highspeed && ehci->fs_i_thresh)
> next = now + ehci->i_thresh;
> else
> next = now;
>
> Why does the driver allow scheduling within the threshold? I though the whole
> point of the threshold value in the HCCPARAMS register was to tell the driver
> the earliest time when it is safe to do scheduling.
>
> Plus, the code doesn't seem to be doing what the comment says for the ICH9
> workaround case (ehci->fs_i_thresh = 1). It seems the && should be an ||
> instead.
>
> The driver seems to be violating the EHCI spec here. Or am I misunderstanding
> what the code is doing?
>
> Thanks.
>
> --
> Paul
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