Re: [PATCH 3.12 033/118] usb: xhci: Link TRB must not occur within a USB payload burst [NEW HARDWARE]

walt
2014-01-21T22:07:11Z

On 01/21/2014 01:51 AM, David Laight wrote:
> From: Sarah Sharp
>> On Mon, Jan 20, 2014 at 11:21:14AM +0000, David Laight wrote:
> ...
>>> A guess...
>>>
>>> In queue_bulk_sg_tx() try calling xhci_v1_0_td_remainder() instead
>>> of xhci_td_remainder().
>>
>> Why? Walt has a 0.96 xHCI host controller, and the format for how to
>> calculate the TD remainder changed between the 0.96 and the 1.0 spec.
>> That's why we have xhci_v1_0_td_remainder() and xhci_td_remainder().
>
> I just wonder how many of those differences are just differences in the
> specification, rather than differences in the hardware implementation.
> In some cases it might be that the old hardware just ignored the value.
>
> I know that the xhci hardware on my ivy bridge cpu does look at that
> value (at least checking for zero), since things failed in subtle ways
> when I got it wrong.
>
> In this case it was just something easy to change that might be worth
> trying. I didn't necessarily expect it to make a positive difference.

David, I tried the one-liner below, which changed nothing AFAICS, but
then I'm not sure it's the change you intended:

--- xhci-ring.c.orig 2014-01-21 13:28:36.396278813 -0800
+++ xhci-ring.c 2014-01-21 13:35:11.410312814 -0800
@@ -3335,7 +3335,7 @@
}

/* Set the TRB length, TD size, and interrupter fields. */
- if (xhci->hci_version < 0x100) {
+ if (xhci->hci_version > 0x100) {
remainder = xhci_td_remainder(
urb->transfer_buffer_length -
running_total);