Messages in this thread | | | Date | Mon, 11 Dec 2006 09:53:15 -0500 (EST) | From | Alan Stern <> | Subject | Re: [linux-usb-devel] [LinuxBIOS] [RFC][PATCH 0/2] x86_64 Early usb debug port support. |
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On Thu, 7 Dec 2006, Peter Stuge wrote:
> On Wed, Dec 06, 2006 at 01:08:14PM -0800, Lu, Yinghai wrote: > > -----Original Message----- > > From: Andi Kleen [mailto:ak@suse.de] > > Sent: Wednesday, December 06, 2006 12:59 PM > > > > >I haven't looked how the other usb_debug works -- if it's polled > > >too then it wouldn't have much advantage. > > > > Need to verify if the two sides of debug cable are identical.
In fact they are not. They are almost identical but not exactly the same.
> I got my device yesterday and after a small plugfest I can confirm > that only one end of the device enumerates when connected to an ICH7 > EHCI driven by 2.6.19.
This is incorrect. Both sides will enumerate. In fact, both sides will enumerate even at full speed (when plugged in to a UHCI controller instead of EHCI).
The difference is that the device will accept power only from one side -- let's call it the A side (the side to the right when you have the PLX logo facing you).
The device is bus-powered, so nothing will happen if the A side isn't plugged in. But if it is then both the A and B sides will enumerate. Their descriptors are almost the same; only the serial numbers are different. The A side's serial number string is "1", and the B side's serial number string is "0". Oddly enough, both sides use the same string index number for the descriptor (3).
> Bus 001 Device 027: ID 0525:127a Netchip Technology, Inc. > Device Descriptor: > bLength 18 > bDescriptorType 1 > bcdUSB 2.00 > bDeviceClass 255 Vendor Specific Class > bDeviceSubClass 0 > bDeviceProtocol 0 > bMaxPacketSize0 64 > idVendor 0x0525 Netchip Technology, Inc. > idProduct 0x127a > bcdDevice 1.01 > iManufacturer 1 NetChip > iProduct 2 NetChip TurboCONNECT 2.0 > iSerial 3 1 ...
> The device is in fact not self-powered. > > My theory is that the same set of descriptors are used for both ends, > but one end has been locked to address 127 in order to work with > simpler debug port drivers that assume it will be there.
No, you are wrong. The device will accept any address on either side.
> I guess that the self-powered error is also to simplify life for > debug port drivers. IIRC most if not all USB power management > concerns are noops for debug ports.
I don't see how it would make life any simpler, but the device certainly does lie about its power source.
Alan Stern
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