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SubjectRe: klists and struct device semaphores
On Mon, 28 Mar 2005, Patrick Mochel wrote:

> How is this related to (8) above? Do you need some sort of protected,
> short path through the core to add the device, but not bind it or add it
> to the PM core?

Having thought it through, I believe all we need for USB support is this:

Whenever usb_register() in the USB core calls driver_register()
and the call filters down to driver_attach(), that routine
should lock dev->parent->sem before calling driver_probe_device()
(and unlock it afterward, of course).

(For the corresponding remove pathway, where usb_deregister()
calls driver_unregister(), it would be nice if __remove_driver()
locked dev->parent->sem before calling device_release_driver().
This is not really needed, however, since USB drivers aren't
supposed to touch the device in their disconnect() method.)

With that change in place we can guarantee that every time a USB driver's
probe() is called, both the interface and the parent device are locked.

I don't know how cleanly this can be implemented. You probably don't want
to lock dev->parent->sem every time, only when needed. Maybe the simplest
approach would be to add a flag in struct bus_type, which could be set for
the USB bus_type and clear for everything else.

Alan Stern

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