On Sat, Dec 04, 2021 at 03:15:15PM +0100, Hans de Goede wrote: > 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. I think this is fixed by 09f736aa9547 ("xhci: Fix commad ring abort, write all 64 bits to CRCR register.") in linux-next and I'll be sending it to Linus in a few hours. thanks, greg k-h
