linux-kernel - Re: [PATCH v1] usb: core: fix pipe creation for get

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Message-ID: <04cb3076-6e34-432f-9400-0df84c054e5c@rowland.harvard.edu>
Date: Thu, 6 Mar 2025 16:43:12 -0500
From: Alan Stern <stern@...land.harvard.edu>
To: Colin Evans <colin.evans.parkstone@...il.com>
Cc: eichest@...il.com, francesco.dolcini@...adex.com,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org, stable@...r.kernel.org,
	stefan.eichenberger@...adex.com
Subject: Re: [PATCH v1] usb: core: fix pipe creation for get_bMaxPacketSize0

On Thu, Mar 06, 2025 at 09:06:23PM +0000, Colin Evans wrote:
> > Please try collecting a usbmon trace for bus 2 showing the problem.
> > Ideally the trace should show what happens from system boot-up, but
> > there's no way to do that.  Instead, you can do this (the first command
> > below disables the bus, the second starts the usbmon trace, and the
> > third re-enables the bus):
> > 
> > 	echo 0 >/sys/bus/usb/devices/usb2/bConfigurationValue
> > 	cat /sys/kernel/debug/usb/usbmon/2u >usbmon.txt &
> > 	echo 1 >/sys/bus/usb/devices/usb2/bConfigurationValue
> > 
> > Then after enough time has passed for the errors to show up, kill the
> > "cat" process and post the resulting trace file.  (Note: If your
> > keyboard is attached to bus 2, you won't be able to use it to issue the
> > second and third commands.  You could use a network login, or put the
> > commands into a shell file and run them that way.)
> > 
> > In fact, you should do this twice: The second time, run it on machine 2
> > with the powered hub plugged in to suppress the errors.
> > 
> > Alan Stern
> 
> Happy to try this, but as it stands there is no such file, or file-like
> thing, on my machine-
> 
> # ls /sys/kernel/debug/usb/usbmon/2u
> ls: cannot access '/sys/kernel/debug/usb/usbmon/2u': No such file or
> directory
> 
> # find /sys/kernel/debug/usb -name "2u"
> #
> 
> # ls /sys/kernel/debug/usb
> devices  ehci  ohci  uhci  uvcvideo  xhci
> 
> 
> It seems something is missing?

Ah -- you have to load the usbmon module first:

	modprobe usbmon

Some distributions do this for you automatically.

Alan Stern