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

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Message-ID: <52DEEF88.8090709@gmail.com>
Date:	Tue, 21 Jan 2014 14:07:04 -0800
From:	walt <w41ter@...il.com>
To:	David Laight <David.Laight@...LAB.COM>,
	'Sarah Sharp' <sarah.a.sharp@...ux.intel.com>
CC:	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: Re: [PATCH 3.12 033/118] usb: xhci: Link TRB must not occur within
 a USB payload burst [NEW HARDWARE]

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);

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