Re: USB devices fail unnecessarily on unpowered hubs

[Andrew Morton]

On Thu, 1 Jun 2006 10:58:43 -0400 (EDT)
Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> 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.

> Configurations that exceed the power budget by less than that amount would
> still be accepted.  I don't know whether this would be enough of a help,
> however.  I've heard of devices that claim to require 200 mA, for
> instance.  It just doesn't seem right to enable them when the upstream hub
> can only provide 100 mA.

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).

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