[U-Boot] [PATCH] usb: Move determination of TT hub address/port into seperate function

[Stefan Bruens]

On Friday 18 December 2015 11:00:19 Hans de Goede wrote:
> Hi,
> 
> On 18-12-15 02:11, Stefan Brüns wrote:
> > Start split and complete split tokens need the hub address and the
> > downstream port of the first HS hub (device view).
> > 
> > The core of the function was duplicated in both host/ehci_hcd and
> > musb-new/usb-compat.h.
> > 
> > Signed-off-by: Stefan Brüns <stefan.bruens at rwth-aachen.de>
> 
> Thanks for working on this, I think I've spotted one small bug though, see
> comments inline.

Ah, sorry for not mentioning this.

Yes, this changes the musb code, but this was on purpose. Rationale:

The ifdef'ed Linux kernel code uses the 1 based port number, whereas U-Boot 
puts a 0 based port number into the register. The reason the 0 based port 
number apparently works can probably be taken from the USB 2.0 spec:

8.4.2.2 Start-Split Transaction Token
... The host must correctly set the port field for single and multiple TT hub 
implementations. A single TT hub implementation *may ignore* the port field.

Actually, as far as I unterstand, a multi TT hub defaults to single TT 
(bAlternateSetting: 0) until switched via SetInterface, so even "port 42" 
would work.

I have somewhat verified this assumption by hardcoding the port number and 
split transactions still work. Used hubs are the RPi onboard SMC9514 and an 
external "05e3:0608 Genesys Logic, Inc. USB-2.0 4-Port HUB". The former is a 
multi TT hub, the latter single TT only.

I have no board with musb, but I think a 0 based port number is wrong.
 
> This function is usb-2 controller / hub specific, maybe rename it to:
> "usb_find_usb2_hub_address_port" to reflect this ?

Yes, sounds reasonable.

Kind regards,

Stefan
	


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