Re: bus powered hub reported as self powered

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On Tue, 31 Mar 2015, Rong Wang wrote:

> Hi all,
> 
> I'm on USB certification of a vendor SoC, and there's a case called
> "Bus powered hub power exceeded test" in the compliance plan defined
> by the usb.org. It requires an error message when a device (Max power
> descriptor >100mA) is attached to an external bus powered hub.
> 
> But when I attached the bus powered hub to Linux (Ubuntu 14.04), I
> found that it always reported as self powered

...

> The hub->mA_per_port is always set as full_load (500mA for usb 2.0
> hub) since reported as self powered hub.
> So when I attach a usb device with ( 100mA < Max power descriptor <=
> 500mA), linux won't show error messages.
> 
> I'm wondering why the bus powered hub reported as self powered? And is
> any switch to make it bus powered?

The reason is simple: The hub is buggy.  It tells the computer that it 
is self-powered even though it isn't.

No, there is no switch to fix it.

Alan Stern

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