Re: USB Storage Device Not Working

On Tue, Nov 13, 2007 at 02:24:19PM -0500, Alan Stern wrote:
> On Wed, 14 Nov 2007, balajirrao wrote:
> 
> > > Remember also that not all EHCI controllers have companions.  Some have
> > > built-in Transaction Translators; I don't know how to force such
> > > controllers to set a port to full speed (maybe it can't be done).  See
> > > how the ehci_is_TDI() test is used.  Your code must work with both
> > > sorts of controllers.
> > > 
> > I think the hardware takes of this if the device wont work under high
> > speed. 
> 
> Maybe, maybe not.  Remember, the only reason you have this problem in 
> the first place is because the device does provide the proper 
> high-speed chirp signal during reset, so it does get connected at high 
> speed -- it just doesn't _work_ at high speed.
> 
Right. In this case, i need to handle it in the code i guess.
> > > And don't forget that none of this should even be attempted if the port 
> > > doesn't belong to the root hub.  There's no way to tell an external hub 
> > > to force a port to full speed.  Your routine needs to test for this.
> > >
> > But suppose, a full speed device is plugged into a external hub. Wont
> > ehci_hcd then hand it over to the companion controller ? 
> 
> No.  If it did, that would mean handing over the external hub plus all 
> the devices attached to it -- including the high-speed devices!
> 
Oh! right. But I am not able to understand why cant the external hub be 
told to force a port to full speed ? I think I need to get a deeper
understanding about how USB works.
> > Ok. Then I need to find out how to indentify a root hub.
> 
> It's easy.  If (hub->hdev->parent == NULL) then it's a root hub, 
> otherwise it isn't.  In other words, root hubs don't have parents.
> 
OK. Alright.
> Alan Stern
> 
Thank you very much, 

balaji rao

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