Re: [PATCH v2] usb: core: add a pre_probe callback for device drivers that may defer

[James Clark <jjc@jclark.com>]

On Fri, 30 Oct 2026 15:41:34 +0000, sashiko-bot@kernel.org wrote:
> However, err_pre_probe only invokes udriver->disconnect(udev) and does not
> undo usb_generic_driver_probe(udev) or usb_autoresume_device(udev) the way
> usb_unbind_device() does:
[...]
> Similarly, on the -ENODEV fallback path where udev->use_generic_driver is set
> to 1 and usb_probe_device() returns -EPROBE_DEFER, won't leaving
> usb_generic_driver_probe(udev) and usb_autoresume_device(udev) in place cause
> the subsequent usb_generic_driver probe to call usb_generic_driver_probe() a
> second time and emit a duplicate USB_DEVICE_ADD notification without an
> intervening USB_DEVICE_REMOVE?

Both of Sashiko's points are correct, but both are pre-existing and this
patch does not change them.

Before the patch, a probe() failure returned straight after
usb_generic_driver_probe() had run, with neither the configuration nor
the runtime PM reference undone. That has been so since commit
c9d503370f24 ("USB: Make it possible to "subclass" usb_device_driver").
The -ENODEV fallback has re-run the generic probe under
usb_generic_driver since commit 88b7381a939d ("USB: Select better
matching USB drivers when available").

The patch deliberately handles a pre_probe() error other than
-EPROBE_DEFER exactly as it handles the same error from probe(), so that
the fallback keeps working. This is stated in the kerneldoc. The only
new code on the error path is the disconnect() call, which undoes what
pre_probe() set up. A complete unwind in usb_probe_device() would be a
separate change.

James