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From: Hans de Goede <>
To: Mathias Nyman <>,
	Pavankumar Kondeti <>,
	Greg Kroah-Hartman <>
Cc: linux-usb <>
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: <> (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):

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"):

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

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.



             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 ` 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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