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[83.28.83.227]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48e53895effsm29069145e9.3.2026.05.06.01.34.46 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Wed, 06 May 2026 01:34:47 -0700 (PDT) Date: Wed, 6 May 2026 10:34:42 +0200 From: Michal Pecio To: "Fischer, Simon" Cc: "regressions@lists.linux.dev" Subject: Re: Lowspeed USB device enumerationg under 5.4.288, but not under 6.8.1 Message-ID: <20260506103442.0ab840ef.michal.pecio@gmail.com> In-Reply-To: <50fff510499b47d09df9317855680552@ipp.mpg.de> References: <50fff510499b47d09df9317855680552@ipp.mpg.de> Precedence: bulk X-Mailing-List: regressions@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 6 May 2026 07:19:53 +0000, Fischer, Simon wrote: > I have been able to reproduce the problem with a current (6.19) > kernel and independent of PREEMPT_RT status. But I have also been > able to identify that the difference between my Ubuntu provided 5.4 > and 6.8 kernels that leads to the problem, is actually the CONFIG_HZ > build config parameter. > > Ubuntu's 6.8 kernel is by default built with CONFIG_HZ=1000, while > the old 5.4 kernel was built with CONFIG_HZ=250. If I rebuild > Ubuntu's 5.4 with 1000Hz, I also cannot talk to the devices, and when > I compile 6.19 or 6.8 with 250Hz, they work (currently running a > rebuilt Ubuntu 6.8.1 with only that one parameter updated, I > sometimes still see errors, but an automatic retry of the driver is > then successful). Quite fascinating ;) BTW, I would still be interested to see 'lsusb -v' of any low-speed isochronous device. Can such a thing seriously work with xhci? > So, a regression this is not :-) > > Since I cannot imagine in what way the system interrupt frequency > would directly affect this part in such a reproducible and > significant manner, I would think it more likely that the USB core or > xhci drivers actually use that setting value somewhere themselves and > maybe wrongly. So this should probably realy go to some other list. > If you know which, I would greatly appreciate you forwarding my > information or telling me where to take it. Per Documentation/admin-guide/reporting-issues.rst, try your best guess which kernel part might be responsible and report there. In short: linux-usb@vger.kernel.org Regards, Michal