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[2001:1c00:c1e:bf00:1054:9d19:e0f0:8214]) by smtp.gmail.com with ESMTPSA id u23sm3836068edi.88.2021.12.04.06.15.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 04 Dec 2021 06:15:16 -0800 (PST) Message-ID: <0a4d723c-221f-a42a-434c-34283a4cdab7@redhat.com> Date: Sat, 4 Dec 2021 15:15:15 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Content-Language: en-US To: Mathias Nyman , Pavankumar Kondeti , Greg Kroah-Hartman From: Hans de Goede Subject: Regression: "xhci: Fix command ring pointer corruption while aborting a command" breaks USB on Intel controllers Cc: linux-usb Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org 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