linux-kernel - Re: [PATCH next] usb: usbfs: Add reset

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Message-ID: <8a16e1c2-fd59-4279-8b36-806a214385b6@rowland.harvard.edu>
Date: Fri, 12 Jul 2024 22:22:24 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Hongyu Xie <xy521521@...il.com>
Cc: gregkh@...uxfoundation.org, oneukum@...e.com, brauner@...nel.org,
	jlayton@...nel.org, xiehongyu1@...inos.cn, jack@...e.cz,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH next] usb: usbfs: Add reset_resume for usbfs

On Fri, Jul 12, 2024 at 11:10:57AM +0800, Hongyu Xie wrote:
> From: Hongyu Xie <xiehongyu1@...inos.cn>
> 
> 
> 
> On 2024/7/11 16:59, Oliver Neukum wrote:
> > 
> > 
> > On 11.07.24 10:43, Hongyu Xie wrote:
> > > During hibernation, usb_resume_interface will set needs_binding to 1 if
> > > the usb_driver has no reset_resume implimentation. The USB interface
> > > will be rebind after usb_resume_complete.
> > > 
> > > Normally, that's fine. But if a USB interface has a matched kernel
> > > driver, and a userspace driver or application is using this USB
> > > interface through usbfs during hibernation, usbfs will be
> > > detatched with the USB interface after resume. And this USB interface
> > > will be bind with a kernel driver instead of usbfs.
> > > 
> > > So add reset_resume to fix this.
> > 
> > The device has lost all settings, yet we continue like nothing
> > changed. That strikes me as a very bad idea. If a device has undergone
> > a reset user space has not requested, we need to return an error upon
> > the next interaction.
> Sorry I don't understand your concern.
> When will "a reset user space has not requested" happen if there is a
> reset_resume in usbfs?

That's what a reset-resume is: a reset that occurs when the device is 
resumed, rather than when the driver has requested a reset.

Alan Stern

> > I am sorry, but this implementation has some fundamental issues.
> > 
> >      Regards
> >          Oliver
> > 
> Regards
> Hongyu Xie