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[83.28.42.246]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-490b56bab73sm954695e9.34.2026.06.02.10.30.51 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Tue, 02 Jun 2026 10:31:04 -0700 (PDT) Date: Tue, 2 Jun 2026 19:30:47 +0200 From: Michal Pecio To: Nikhil Solanke Cc: Alan Stern , linux-usb@vger.kernel.org, gregkh@linuxfoundation.org, mathias.nyman@linux.intel.com, sakari.ailus@linux.intel.com, katieeliu@tencent.com, johannes.bruederl@gmail.com, kees@kernel.org, dengjie03@kylinos.cn, limiao@kylinos.cn, wse@tuxedocomputers.com, dev@a1rm4x.com, vahnenko2003@gmail.com, cs@tuxedo.de, lijiayi@kylinos.cn, oneukum@suse.com, bence98@sch.bme.hu, eeodqql09@gmail.com Subject: Re: USB: Request for guidance investigating configuration descriptor enumeration failure Message-ID: <20260602193047.5fe03b8d.michal.pecio@gmail.com> In-Reply-To: References: <20260531101612.332151d8.michal.pecio@gmail.com> <20260531123843.736bd69a.michal.pecio@gmail.com> <3b79ba92-1c51-420b-a5d2-8a358cafdbf6@rowland.harvard.edu> <20260601084846.433bfc51.michal.pecio@gmail.com> Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 1 Jun 2026 14:31:59 +0530, Nikhil Solanke wrote: > It didn't occur to me before, but since i had a patched kernel which > enumerated and initialized the device properly, i was able to do a usb > device passthrough/redirect of the controller when it is in xinput > mode. I have utilized libvirt for this purpose. I tried doing what > Michal did by using qemu cmdline directly and specifying the location > for pcap file, but for some reason the pcap file only contained > request packets. there were no response packets. It may be a QEMU bug because the same happens to me when I pass through host devices. The full trace I posted was from a QEMU emulated device. You can also run Wireshark on the Linux host and it seems that QEMU forwards all control requests unmodified to the device and Wireshark records responses too. But it also records some additional string descriptor requests (apparently originated by QEMU) and any random traffic on the bus to other devices. I passed through some serial dongles that my Windows had no drivers for and I found that it only issues two requests for the device descriptor, one 255 byte request for the configuration descriptor (possibly another one if configuration exceeds 255 bytes, will try to find such a device) and a few requests for string descriptors. That's it. The other junk only appears when I install class driver for the device. And I still haven't installed Wireshark in QEMU Windows, but it appears that Windows Wireshark only sees that class driver traffic and nothing from core USB subsystem. So it's useless for our purpose. > I have attached the wireshark captures from the linux guest as well as > the libvirt xml. i also had tried using ehci/usb 2 on the guest. I only mentioned EHCI to ask if any of the hosts that you tried had it. The point was to rule out possibility of xhci-hcd bug, when we still believed that Windows issues identical 9 byte requests on the same xHCI controller and somehow succeeds. Now we know that Windows Wireshark traces were misleading and the use of 255 byte requests likely explains how Windows enumerates the device successfully and Linux fails without your patch. Regards, Michal