From: Hans de Goede <hdegoede@redhat.com>
To: Mathias Nyman <mathias.nyman@intel.com>,
Pavankumar Kondeti <pkondeti@codeaurora.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb <linux-usb@vger.kernel.org>
Subject: Regression: "xhci: Fix command ring pointer corruption while aborting a command" breaks USB on Intel controllers
Date: Sat, 4 Dec 2021 15:15:15 +0100 [thread overview]
Message-ID: <0a4d723c-221f-a42a-434c-34283a4cdab7@redhat.com> (raw)
Hi All,
There are several bug reports (arch and Fedora) about USB problems
starting with kernel 5.14.14 (5.14.13 is ok):
https://bugzilla.redhat.com/show_bug.cgi?id=2019788
https://bbs.archlinux.org/viewtopic.php?pid=2006862
And 5.16.6, which has the hub address0_mutex fixes does not
fix these problems for some users.
Looking at the history between those 2 commit ff0e50d3564f
("xhci: Fix command ring pointer corruption while aborting a command"):
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ff0e50d3564f
stood out to me as a possible cause of this. So I've build
a test 5.15.6 kernel for Fedora users with that commit reverted
and 2 users have now reported that this fixes things for them
(see https://bugzilla.redhat.com/show_bug.cgi?id=2019788).
The reason why this stood out to me is because doing a 32 bit
write over a possibly 64 bit databus to the xHCI controller may
result in the hw doing a 64 bit read + modify 32 bit + 64 bit write,
so I think that the following is happening after the commit:
sw: read 32 bit
hw: read 64 bit, return 32 bit
sw: modify it
sw: write 32 bit
hw: read 64 bit
hw: modify 32 bit of 64 bit wor5d
hw: write 64 bit
Which actually makes the chances of hitting the problem the commit
tries to fix larger on controllers using a 64 bit data bus.
Note this is just a theory, but it seems plausible to me.
All problem reports are people using integrated Intel xHCI controllers
which I believe are likely to use a 64 bit data-bus.
Regards,
Hans
next reply other threads:[~2021-12-04 14:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-04 14:15 Hans de Goede [this message]
2021-12-05 6:46 ` Regression: "xhci: Fix command ring pointer corruption while aborting a command" breaks USB on Intel controllers Thorsten Leemhuis
2021-12-05 8:20 ` Greg Kroah-Hartman
2021-12-05 8:20 ` Greg Kroah-Hartman
2021-12-05 12:48 ` Greg Kroah-Hartman
2021-12-07 0:46 ` Tobias Bachmann
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