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

[Oliver Neukum <Oliver.Neukum@lrz.uni-muenchen.de>]

Am Mittwoch, 5. Juni 2002 16:19 schrieb David Brownell:
> Oliver Neukum wrote:
> >>>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?  :)
> >
> > OK, but where do we handle the case where resumption is impossible
> > because the device has been unplugged ?
>
> If that's not already handled, it'd be a bug in the hub driver.

Well, how will we handle it with respect to the resume function ?
Do we report failure if there's no longer a device at the physical
location ? IMHO we do.
Do we have checks in the core for identity, or do we leave that
to the driver ? I am not sure.

> >>>>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.
> >
> > That is not the entire truth.
> > The hub will be told to resume first. If we than scan the physical bus
> > and initiate initialisation of the devices found, there'll be chaos
> > once the "driverfs" layer tells devices to resume.
>
> You said "initiate initialisation"; that's normally called "enumeration".
> Which by definition is NOT done for a USB device being resumed!!!!

Now I am puzzeled. There must be some misunderstanding.
Could you please outline, how we deal with a resumption
if the devices lost power under the new scheme ?

> > The point of suspend/resume cycles is that the system is restored
> > to the state it had. IP, mac, filtering etc... must be restored, not only
> > names.
>
> Then there's always reality to deal with.  Like when a network link gets
> removed during suspend.

Yes, that should concern the network layer, not a device driver.
But the device driver must reset MAC and IP at least.

> > In fact, if we have persistent names we don't need to care about names.
>
> Erm, that doesn't make sense.  Having them persistent means someone is
> caring a heck of a lot about names and assignment policies.

We meaning device driver maintainers ;-)

	Regards
		Oliver

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