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Date:   Wed, 24 Nov 2021 08:04:21 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Jupiter <jupiter.hce@gmail.com>
Cc:     linux-usb <linux-usb@vger.kernel.org>
Subject: Re: Kernel 5.10 USB issues
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On Wed, Nov 24, 2021 at 11:46:06AM +1100, Jupiter wrote:
> Hi,
> 
> I connected a USB bus between an iMX6ULZ and an 4G LTE modem, it was
> running well in kernel 4.19.75. I've just upgraded kernel to 5.10.59,
> the USB is broken, the USB drivers were disconnected / connected
> repeatedly:
> 
> [12781.730889] usb 1-1: USB disconnect, device number 84
> [12781.808317] option1 ttyUSB0: GSM modem (1-port) converter now
> disconnected from ttyUSB0

That is usually a hardware problem, the kernel can not disconnect a
device from the bus through software.

But, if 4.19 is working, can you use 'git bisect' between the two
kernels to find what caused the problem?

thanks,

greg k-h