关于kernel2.6中USB host controller driver 的问题

2.6在s3c2410上usb host不工作的直接结果就是提示110错误：
usb 1-1: device descriptor read/64, error -110

追踪错误代码，我们来看看能不能找到导致这个错误的线索。

include/asm-generic/errno.h
#define EPROTO 71 /* Protocol error */
#define EILSEQ 84 /* Illegal byte sequence */
#define ETIMEDOUT 110 /* Connection timed out */

Documentation/usb/error-codes.txt
-EPROTO (*, **) a) bitstuff error
b) no response packet received within the
prescribed bus turn-around time
c) unknown USB error

-EILSEQ (*, **) a) CRC mismatch
b) no response packet received within the
prescribed bus turn-around time
c) unknown USB error

-ETIMEDOUT (**) No response packet received within the prescribed
bus turn-around time. This error may instead be
reported as -EPROTO or -EILSEQ.

由此我们可以判断，这个错误与 usb 设备的超时有关。报告这个错误的地方在drivers/usb/core/hub.c中的hub_port_init部分，由于 usb_get_device_descriptor获取 usb 设备信息的时候产生了超时。这样基本可以确定三种情况，1、usb 设备及接口有问题；2、usb core有问题；3、usb driver有问题。
我们可以很容易地排除1和2的可能性，问题应该在usb driver implement部分造成的。2.6的usb driver把usb规范中对usb接口的操作集中到了core里面，针对不同设备的implement分别归为host、gadget、storage 等。基本确定问题就在ohci-s3c2410.c里。

跟踪进入ohci-s3c2410.c，这里面主要完成s3c2410 usb host设备的初始化工作，包括电源、时钟、寄存器等。

其实很多问题在互联网上已经被遇到和解决，我们要做的就是多参考别人的成功经验，这样可以节省时间，同时能够帮助我们找到一些思路。借助google这双强大的翅膀，我们来看看能找到什么：

http://www.linux-usb.org/FAQ.html#ts6

Q: Why doesn’t USB work at all? I get “device not accepting address”.

A: You may have some problem with your PCI setup that’s preventing your USB host controller from getting hardware interrupts. When Linux submits a request, but never hears back from the controller, this is the diagnostic you’ll see. To see if this is the problem, look at /proc/interrupts to see if the interrupt count for your host controller driver ever goes up. If it doesn’t, this is the problem: either your BIOS isn’t telling the truth to Linux (ACPI sometimes confuses these things, or setting the expected OS to windows in your BIOS), or Linux doesn’t understand what it’s saying.

Sometimes a BIOS fix will b