Message-ID: <20070509170742.GA29806@kroah.com>
Date:	Wed, 9 May 2007 10:07:42 -0700
From:	Greg KH <greg@...ah.com>
To:	david@...g.hm
Cc:	Cornelia Huck <cornelia.huck@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Adrian Bunk <bunk@...sta.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Duncan Sands <duncan.sands@...h.u-psud.fr>
Subject: Re: Please revert 5adc55da4a7758021bcc374904b0f8b076508a11
	(PCI_MULTITHREAD_PROBE)

On Wed, May 09, 2007 at 09:18:10AM -0700, david@...g.hm wrote:
>  On Wed, 9 May 2007, Cornelia Huck wrote:
> 
> > On Wed, 9 May 2007 02:25:10 -0700 (PDT),
> > david@...g.hm wrote:
> >
> >> makeing up an example
> >>
> >> today the process would be
> >> call driver X to initialize it's devices.
> >>
> >> driver X follows these steps
> >>
> >> 1. see if a compatible chipset/device appears to be available
> >>
> >> 2. initialize the chipset/device (loading firmware)
> >>
> >> 3. query the now partially initialized chipset/device to see what specific
> >> options are enabled in the hardware
> >>
> >> 4. for each 'thing' that's enabled in hardware, initialize and register
> >> it.
> >
> > The sync ->probe() could return after step 1 (when it is clear the
> > driver wants to bind to the device). The remainder should be done in
> > the async function, so that the bus could go on with other devices. The
> > driver should then signal when it is done with its registrations.
> 
>  but then won't the devices get registered in a random order? (i.e. whenever 
>  the async portion finishes the probing and finds the details of what there 
>  is to register)

So?  We have busses today that have devices get registered in random
order, our userspace tools can handle it just fine now.

> >> to acommodate both of these device models it seems to me that you can't
> >> defice either
> >> async followed by sync
> >> or
> >> sync followed by async
> >> but instead need to support the combined
> >> sync followed by async followed by sync.
> >>
> >> now, it's very possible that I'm mistaken and one of the two-part models
> >> can be used for everything, if so then it's definantly simpler to do so.
> >
> > Hm, maybe I'm dense, but I really don't understand the problem here.
> > Why should (optional) sync followed by (optional) async followed by bus
> > synchonization not cover all cases? The async portion can also do some
> > "sync" stuff and then signal completion, can't it?
> >
> > If you're worried about notifications to userspace, you could first
> > suppress the add uevent via uevent_suppress and then generate it when
> > you signal completion to the bus.
> 
>  I'm not worried about notification to userspace, I'm worried about devices 
>  getting registered during the async stage appearing in different orders on 
>  different boots due to different timeings.
> 
>  if you can identify the device well enough to register it quickly then the 
>  approach that Linus proposed works well, which is
> 
>  sync probe, identify devices, register devices
>  async initialize devices
>  wait for all async to complete
> 
>  however I'm talking about cases where you can't fully identify the devices 
>  (at least not well enough to register them with the kernel) and am saying 
>  that doing
> 
>  sync probe
>  async initialize device, register device
>  wait for all async to complete
> 
>  results in unpredictable device ordering, but if instead you did
> 
>  sync probe
>  async initialize device
>  sync wait for all async to complete, register device
> 
>  you can get back to predictable ordering

No, don't worry about that, the ordering can be made different due to
any number of different things (bios upgrade, new device added, phase of
the moon, etc.)  So stop worrying about being predictable, we have never
really had that...

thanks,

greg k-h
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