Re: USB devices fail unnecessarily on unpowered hubs

[Alan Stern <stern@rowland.harvard.edu>]

On Thu, 1 Jun 2006, Andrew Morton wrote:

> On Thu, 1 Jun 2006 10:58:43 -0400 (EDT)
> Alan Stern <stern@rowland.harvard.edu> wrote:
> 
> > As an alternative, we could allow an "over-budget window" of say 10%.  
> 
> That, plus we should provide a suitable i-know-what-im-doing user override,
> with the appropriate warnings, as well as a printk which directs users to
> this option when we decided to disable their device.

The user override already exists, as do the appropriate warnings.  Daniel 
Drake just added a printk explaining why the device was not configured, 
although it doesn't tell how to configure the device by hand.  Perhaps a 
FAQ entry at www.linux-usb.org would be appropriate.

> The power supply spec is a conservative minimum, whereas the device spec is
> a worst-case maximum.  One would expect a lot of devices will work OK when
> run "out of spec".
> 
> (Goes away and pats all his 240V plugpacks which are happily working off 110V).

They probably will.  The question is, how far out-of-spec should the 
kernel allow by default?  200% is likely to be too far (your plugpacks 
notwithstanding).

Alan Stern

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