Re: [PATCH] USB: disable autosuspend by default for non-hubs

Am Montag 20 August 2007 schrieb Alan Stern:
> On Mon, 20 Aug 2007, Oliver Neukum wrote:
> 
> > Am Montag 20 August 2007 schrieb Alan Stern:
> > > This patch (as965) disables autosuspend by default for all USB devices
> > > other than hubs.  We are seeing too many devices that can't suspend or
> > > resume properly, the blacklist is growing unreasonably quickly, and
> > > this sort of thing should be handled in userspace.
> > 
> > This is unreasonably broad. The drivers may dictate that a device cannot
> > autosuspend by not setting the flag. Why do you want to override their
> > decision if they do set the flag?
> 
> Three reasons:
> 
>      1. It takes time to load driver modules, especially during bootup
> 	when lots of things are happening.  During that time a device
> 	can be autosuspended by mistake, even though the driver (had
> 	it been present) would not have allowed it.

How can that happen? The proposal is to not suspend devices without drivers
unless told via sysfs and leave the decision for devices with drivers to
the drivers.

>      2. Drivers don't know about all possible bad devices.  By erring
> 	on the side of safety we can prevent (for example) storage 
> 	devices that work in 2.6.22 from breaking in 2.6.23.
> 
>      3. It isn't a complete override of the driver's decision, since
> 	the user can still enable autosuspend.  In fact there should be
> 	a user program that checks each USB device, as it is detected,
> 	against a database to see whether it should be allowed to
> 	autosuspend and what the idle delay should be.

But you are forcing them through yet another hoop in user space.
Drivers can do anything they want with their interfaces. It makes
no sense to force it through user space for every driver. We must
trust drivers.

	Regards
		Oliver

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