linux-kernel - Re: Strange problem with USB device

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Date:   Tue, 8 Jun 2021 14:53:14 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Larry Finger <Larry.Finger@...inger.net>
Cc:     linux-usb@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        ierturk@...e.org
Subject: Re: Strange problem with USB device

On Tue, Jun 08, 2021 at 01:37:07PM -0500, Larry Finger wrote:
> On 6/8/21 1:20 PM, Alan Stern wrote:
> > One thing you might try is to turn on USB debugging before
> > plugging in the device:
> > 
> > echo 'module usbcore =p' >/sys/kernel/debug/dynamic_debug/control
> > 
> > The additional information this adds to the dmesg log may be
> > helpful.
> 
> The BT device is part of the same card as the PCIe wifi device, thus
> there is no "plugging" it in a conventional sense.

I don't get it.  If this is a PCIe device, why should it appear 
on a USB bus?  Wouldn't you expect it to show up as a PCI device 
on a PCI bus instead?

>  Is there some way to
> add the usbcore debugging statement to the kernel options line at boot
> time?

Yes.  Use the kernel boot-line parameter:

	usbcore.dyndbg="=p"

FYI, how to use dynamic debugging is explained at length in the 
kernel source file 
Documentation/admin-guide/dynamic-debug-howto.rst.

Alan Stern

> As I told GregKH, I am having the person with the problem try a rescue
> system with a 5.12 kernel.
> 
> Larry
>