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List:       linux-usb-devel
Subject:    Re: [linux-usb-devel] i.MX21 USB driver - hub 1-0:1.0: Cannot
From:       Alan Stern <stern () rowland ! harvard ! edu>
Date:       2007-09-27 17:06:59
Message-ID: Pine.LNX.4.44L0.0709271300180.7735-100000 () iolanthe ! rowland ! org
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On Thu, 27 Sep 2007, Midhun A wrote:

>    I am investigating this problem. I have the following observations:
> 
> 1. As soon as I plug in my flash drive, the port status is 0x103 -
> which I could find from the USB specification that the port is powered
> (bit 8), port is enabled (bit 1) and that a device has been connected
> to the port (bit 0). The port status change bits are 0x0.

That isn't what it should be.  You should see connect status and 
connect-change status, and you shouldn't see port enabled.  Ports 
aren't supposed to get enabled until they have been reset.

> 2. The kernel then says:
>  "usb 1-2: new full speed USB device using imx21-hc and address 2"

At this point the system tries to reset the port.  You appear to have 
omitted this step.

> 3. The system now tries to read the port status again and it gets
> 0x101 - which is port is powered (bit 8) and device is connected to
> the port (bit 0). But the port status change are 0x12 - which is port
> reset is complete (bit 4) and PORT IS DISABLED DUE to Port_Error
> condition (bit 1).

Right.  The reset is supposed to leave the port enabled.  If it doesn't 
then something is wrong.

>   I want to know what this Port_Error condition is. I have read
> section 11.8 of the specification. But it does not say how to resolve
> this error.

The USB spec won't help; it's too general.  You need to know the
details of the behavior of the imx21.  If you can hook up an 
oscilloscope and watch the signal levels change, that might give you 
some ideas.  It could be something as simple as a bad capacitance.

Alan Stern


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