学步园

Linux-USB Gadget : Part 6: dummy hcd 驱动简介

作者： zjujoe 转载请注明出处

Email：zjujoe@yahoo.com

BLOG：http://blog.csdn.net/zjujoe

前言

一直没有弄明白 dummy hcd 到底有什么用，因为它位于 gadget 目录里，以为是一个软件模拟的 udc 驱动。但是想想 gadget
驱动功能需要主机端触发，不知道这么一个假的 udc 驱动到底怎么触发数据传输。

今天简单的分析了一下代码。发现原来 dummy hcd 包含了 host controller 及 device controller 驱动， 这样， 就可以在同一台机器上进行 host 和 device 端的传输。如果你正在写主机端的 client 驱动或者设备端的 gadget 驱动，使用 dummy hcd 是很高效的。 下面简单分析一下这个驱动。

代码

看一下初始化代码：

 

2021 static int __init init (void)

2022 {

2023        
int     retval;

2024

2025         if (usb_disabled
())

2026                
return -ENODEV;

2027

2028         retval
= platform_driver_register
(&dummy_hcd_driver);

2029         if
(retval < 0)

2030                
return retval;

2031

2032         retval
= platform_driver_register
(&dummy_udc_driver);

2033         if
(retval < 0)

2034                
goto err_register_udc_driver;

2035

2036         retval
= platform_device_register
(&the_hcd_pdev);

2037         if
(retval < 0)

2038                
goto err_register_hcd;

2039

2040         retval
= platform_device_register
(&the_udc_pdev);

2041         if
(retval < 0)

2042                
goto err_register_udc;

2043         return
retval;

2044

2045 err_register_udc:

2046         platform_device_unregister
(&the_hcd_pdev);

2047 err_register_hcd:

2048         platform_driver_unregister
(&dummy_udc_driver);

2049 err_register_udc_driver:

2050         platform_driver_unregister
(&dummy_hcd_driver);

2051         return
retval;

2052 }

2053 module_init
(init);

 

同时注册了 usb 主机端、设备端 的驱动及设备。再看一下该“设备”提供的 “端点”:

 

124
static const char *const ep_name [] =
{

125         ep0name,                                /*
everyone has ep0 */

126

127         /* act like a net2280: high
speed, six configurable endpoints */

128         "ep-a", "ep-b",
"ep-c", "ep-d", "ep-e", "ep-f",

129

130         /*
or like pxa250: fifteen fixed function endpoints */

131         "ep1in-bulk", "ep2out-bulk", "ep3in-iso", "ep4out-iso",
"ep5in-int",

132         "ep6in-bulk", "ep7out-bulk",
"ep8in-iso",
"ep9out-iso", "ep10in-int",

133         "ep11in-bulk", "ep12out-bulk", "ep13in-iso", "ep14out-iso",

134                
"ep15in-int",

135

136         /*
or like sa1100: two fixed function endpoints */

137         "ep1out-bulk", "ep2in-bulk",

138 };

 

可见，dummy_hcd 提供了丰富的端点类型。可以用来测试各种上层驱动。

 

再研究一下数据是怎么在host 端和 client 端进行传输的， 我们使用
kft 工具画出一次数据传输的函数调用流程：

 

 

数据通过 usb_submit_urb 提交后，函数
dummy_timer 会调用 transfer 函数进行数据传输：

 

1065
/* transfer up to a frame's worth; caller must own lock */

1066
static int

1067
transfer
(struct dummy
*dum, struct urb
*urb, struct dummy_ep
*ep, int limit)

1068
{

1069         struct dummy_request    *req;

1070

。。。

1111                         /* else transfer
packet(s) */

1112                         ubuf = urb->transfer_buffer
+ urb->actual_length;

1113                         rbuf = req->req.buf +
req->req.actual;

1114                         if (to_host)

1115                                 memcpy (ubuf,
rbuf, len);

1116                         else

1117                                 memcpy (rbuf,
ubuf, len);

1118                         ep->last_io = jiffies;

。。。

 

这里， transfer 函数会调用 memcpy 进行数据 ”传输”。

 

再看一下控制传输， 先看调用图：

以及代码：

1238 /* drive both sides of the transfers; looks
like irq handlers to

1239
 * both drivers except the
callbacks aren't in_irq().

1240
 */

1241
static void dummy_timer
(unsigned long _dum)

1242
{

。。。

1336                
/* handle control requests */

1337                
if (ep == &dum->ep [0] && ep->setup_stage) {

1338                         struct usb_ctrlrequest          setup;

1339                         int                             value = 1;

1340                         struct dummy_ep                 *ep2;

1341                         unsigned                        w_index;

1342                         unsigned                        w_value;

1343

1344                 
       setup =
*(struct usb_ctrlrequest*)
urb->setup_packet;

1345                         w_index = le16_to_cpu(setup.wIndex);

1346                         w_value = le16_to_cpu(setup.wValue);

1347                         if (le16_to_cpu(setup.wLength)
!=

1348                                         urb->transfer_buffer_length)
{

1349                                 maybe_set_status
(urb, -EOVERFLOW);

1350                                 goto
return_urb;

1351                         }

1352

。。。

1366

1367                         /* gadget driver
never sees set_address or operations

1368                          * on standard feature
flags.  some hardware doesn't

1369                          * even expose them.

1370                          */

1371                         ep->last_io = jiffies;

1372                         ep->setup_stage =
0;

1373                         ep->halted = 0;

1374                         switch (setup.bRequest)
{

1375                         case USB_REQ_SET_ADDRESS:

1376                                 if (setup.bRequestType
!= Dev_Request)

1377                                         break;

1378                                 dum->address =
w_value;

1379                                 maybe_set_status
(urb, 0);

1380                                 dev_dbg (udc_dev(dum),
"set_address = %d/n",

1381                                                
w_value);

1382                                 value = 0;