Re: [linux-usb-devel] Re: hotplugging to deal with firmware download

[David Brownell <david-b@pacbell.net>]

>>>I see no plan to do it with the present power management system.
>>>The devices are simply assumed to switch from suspended to working
>>>in kernel space. Suspended may mean off here.
>>
>>Well, the usb device drivers _do_ need individual suspend()/resume()
>>callbacks.  The "new device model" stuff exists in part to ensure
>>that devices get those calls appropriately.
>
> I agree. But usbcore should help as far as possible.

What were you thinking would transform the "device model" level
suspend/resume calls into USB level ones?  :)


>>For example, suspending a bus-powered hub would need to morph into
>>disconnecting the devices it could no longer power ... and in your
>>case, suspending a network device that discards its firmware would
>>also need to morph into a disconnect.
>
> That's exactly what you must _not_ do, you need to retain the information 
> which devices was on which port to resume correctly.

Why would that be?  In those cases, the device MUST re-enumerate from
scratch, there will be no USB state to resume.  In those cases the
devices can't suspend; they can only disconnect/reconnect.

And it'd be pointless, since if any device driver wants to save
information about devices across reconnects -- like usb-storage does
today -- it has all the tools it needs to do that already.  There's
no need to bloat the core with such stuff.

Given that userspace tools can already be used to make network device
names be pseudo-stable ("eth2" is always the one with address NN), and
network drivers can even request specific names ("eth3") I don't see
any reason any network device driver should want such functionality.

- Dave



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