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List:       linux-usb-devel
Subject:    Re: [linux-usb-devel] [linux-pm] Re: The evilness of struct
From:       "Rafael J. Wysocki" <rjw () sisk ! pl>
Date:       2007-09-28 20:29:06
Message-ID: 200709282229.06825.rjw () sisk ! pl
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On Friday, 28 September 2007 17:11, Alan Stern wrote:
> On Fri, 28 Sep 2007, Rafael J. Wysocki wrote:
> 
> > > That's because the notifications go up the device tree, not down.  When 
> > > a child is suspended, the parent is notified.  Then if the driver sees 
> > > that all the children are suspended, the parent can be suspended as 
> > > well.
> > > 
> > > Oliver has been trying to subvert this model by making usb-storage 
> > > responsible for suspending the SCSI disk and CD/DVD drivers, which are 
> > > located beneath it in the device tree.  I've been trying to convince 
> > > him that the proper way to handle things is to let the SCSI drivers 
> > > decide for themselves when their devices can be suspended, and then 
> > > have them inform usb-storage.
> > 
> > Yes, I think that the SCSI layer should decide.
> > 
> > I guess that the SCSI layer is not really autosuspend-aware, is it?
> 
> Not yet.  I would like it to become autosuspend-aware.  Oliver wants to
> avoid that by keeping all the awareness in usb-storage.  (But then what
> about all the other SCSI host-adapter drivers?  Will they each have
> their own way of deciding when a SCSI device can be suspended?)

IMO, this is a more general issue.

The problem, as I see it, is which layer of drivers should be responsible of
making autosuspend decisions if there are many layers stacked on top of one
another.

I think that it should be the layer which communicates with processes, eg. via
syscalls.

Greetings,
Rafael

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