Re: [PATCH] usb: usbfs: Add reset_resume callback to usbfs.

[Alan Stern]

On Fri, Aug 22, 2025 at 10:46:02AM +0800, ccc194101@xxxxxxx wrote:
> From: chenchangcheng <chenchangcheng@xxxxxxxxxx>
> 
> When an Apple device is inserted into the host, and the host
> wakes up from S3/S4 power states, if the reset_resume process
> is triggered, the absence of a reset_resume callback in usbfs will
> cause the device to unbind.
> By adding a reset_resume callback to usbfs and reporting REMOVE and ADD
> uevents in reset_resume, the userspace is prompted to reissue commands
> to re-establish the binding with usbfs.

usbfs has no way to inform userspace when the device is reset.  This is 
true for normal resets as well as for reset-resumes (no pre_reset, 
post_reset, or reset_resume callbacks).  I don't see any point in trying 
to add support for the latter but not the former.

Unbinding the device forces userspace to re-open the device file and 
establish a new binding.  How does adding REMOVE and ADD uevents make 
the situation any better than it already is?

Alan Stern