[U-Boot-Users] U-Boot USB on MIPS

[Hans Zuidam]

Hi,

I am trying to get the PCI OHCI driver (drivers/usb_ohci.c in the u- 
boot-usb.git archive) to work on a MIPS 4KEc system, but facing a  
couple of problems:

Endianess poses a problem in that the 4KEc runs in little endian mode  
and #defining LITTLEENDIAN still introduces some swaps that should  
not be done.  My guess is that USB has only been used on big endian  
CPUs.  For the time being I have removed all the swaps, just to get  
the driver going.  Once the driver is working I will put the swaps  
back in.

A more nasty problem has to do with address spaces: MIPSen always use  
virtual memory, even when the MMU is off.  For example: kernel code  
(and thus U-Boot too) runs in host memory from 0x80000000 to  
0x9FFFFFFF (cached) or 0xA0000000 to 0xBFFFFFFF (uncached).  Both  
these memory spaces are mapped to physical memory 0x00000000 to  
0x1FFFFFFF.

As far as I can see the PCI OHCI driver does not do address  
translations when moving addresses (pointers) to and from the host  
controller.  For example the HcHCCA register is programmed with a  
virtual address, not the physical address as it should be.  Likewise  
for the HcControlHeadED register and the other memory pointers used  
by the controller.  This leads to PCI bus errors (e.g. Received  
Master Abort errors) when the driver initialises the root hub.

The instances where these registers are written are easy enough to  
find and fix, but the code manipulating the endpoint descriptors is  
much more difficult.  It is hard to figure out when a particular  
pointer is handed off to the controller and when it is actually used  
by the CPU.

The original Linux driver (from a 2.4 release if I am not mistaken)  
does cater for the translation between kernel virtual memory  
addresses and device physical addresses.  To fix the address  
translations my idea is to take the Linux OHCI driver from which the  
U-Boot driver was derived and do a careful comparison of the two,  
moving the address translations back into the U-Boot driver.

Therefore two questions:
	From which Linux kernel version is the U-Boot PCI OCHI driver derived?
	Is the above approach viable or is there a better strategy?

Thanks in advance.

With kind regards,
Hans Zuidam
--
Hans Zuidam
De Koppele 136, 5632 LD Eindhoven, The Netherlands
Tel. +31 40 2481546, Mob. +31 6 42345456
h.zuidam at computer.org