Xilinx VC709开发板，对应的程序中有个performance mode，是查看DMA性能的。
该板子的DMA驱动为xdma_v7.ko，在路径linux_driver_app/driver/xdma中。
选择performance mode后，该模式只使用一个DMA engine(即engine 0)，其有2个通道分别为TX和RX，
对应的设备驱动为xrawdata0.ko，在路径linux_driver_app/driver/xrawdata0中,对应的驱动源程序为sgusr.c。
xraw_data0的驱动需要向XDMA的驱动注册，以完成相应的接口，其在系统中的接口为一个字符文件/dev/xraw_data0。
下面我们具体来看sgusr.c文件的源码。
1.文件前面是各种定义，寄存器地址等。
第277-278行，定义RawTestMode = TEST_STOP,即初始化时，没有开始测试。
RawMinPktSize为64 Byte,RawMaxPktSize为4个内存页(4page=4*4096=32768 Byte)。
2.初始化函数
static int __int rawdata_int(void)
第1457行，初始化xraw_data0的状态为 INITIALIZED,后面依次初始化3个spin_lock.
第1471行，调用alloc_chrdev_region（），请求系统给xrawDev设备分配设备号。
如果设备号分配成功，申请代表字符设备的struct cdev结构来初始化xrawCdev指针,成功后，初始化对应的文件操作函数到这个设备上，即初始化file_operations类型的xrawDevFileOps结构体（1489-1494行），最后第1498行调用cdev_add（）将设备加入内核。
xraw_data0作为使用DMA的应用，需要实现xdma驱动的对应功能的callback函数，想DMA注册。
从第1516行开始，对应的先指定ufuncs中对应的callback，然后使用DmaRegister()将自己注册到base DMA驱动中，比如第1542行DmaRegister (ENGINE_TX, MYBAR, &ufuncs, BUFSIZE))，将xraw_data0应用注册XDMA的ENGINE_TX号引擎上，对应的BAR寄存器地址为MYBAR,对应的函数调用为ufuncs,正常的包大小为BUFFSIZE.
DmaRegister()的实现在xdma驱动源码的xdma_user.c中1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128/*****************************************************************************/
/**
* This function must be called by the user driver to register itself with
* the base DMA driver. After doing required checks to verify the choice
* of engine and BAR register, it initializes the engine and the BD ring
* associated with the engine, and enables interrupts if required.
*
* Only one user is supported per engine at any given time. Incase the
* engine has already been registered with another user driver, an error
* will be returned.
*
* @param engine is the DMA engine the user driver wants to use.
* @param bar is the BAR register the user driver wants to use.
* @param uptr is a pointer to the function callbacks in the user driver.
* @param pktsize is the size of packets that the user driver will normally
* use.
*
* @return NULL incase of any error in completing the registration.
* @return Handle with which the user driver is registered.
*
* @note This function should not be called in an interrupt context
*
*****************************************************************************/
void * DmaRegister(int engine, int bar, UserPtrs * uptr, int pktsize)
{
Dma_Engine * eptr;
u64 barbase;
u32 barbase;
int result;
log_verbose(KERN_INFO "User register for engine %d, BAR %d, pktsize %d\n",
engine, bar, pktsize);
if(DriverState == PM_PREPARE)
{
log_verbose(KERN_ERR "DMA driver state %d - entering into Power Down states\n", DriverState);
return NULL;
}
if(DriverState != INITIALIZED)
{
log_verbose(KERN_ERR "DMA driver state %d - not ready\n", DriverState);
return NULL;
}
if((bar < 0) || (bar > 5)) {
log_verbose(KERN_ERR "Requested BAR %d is not valid\n", bar);
return NULL;
}
if(!((dmaData->engineMask) & (1LL << engine))) {
log_verbose(KERN_ERR "Requested engine %d does not exist\n", engine);
return NULL;
}
eptr = &(dmaData->Dma[engine]);
barbase = (dmaData->barInfo[bar].baseVAddr);
barbase = (u32)(dmaData->barInfo[bar].baseVAddr);
if(eptr->EngineState != INITIALIZED) {
log_verbose(KERN_ERR "Requested engine %d is not free\n", engine);
return NULL;
}
/* Later, add check for reasonable packet size !!!! */
/* Later, add check for mandatory user function pointers. For optional
* ones, assign a stub function pointer. This is better than doing
* a NULL value check in the performance path. !!!!
*/
/* Copy user-supplied parameters */
eptr->user = *uptr;
eptr->pktSize = pktsize;
/* Specify user-specific version information register. Note that this is
* in the BAR0 space.
*/
uptr->versionReg = (dmaData->barInfo[0].baseVAddr) + 0x9000;
uptr->versionReg = (u32)(dmaData->barInfo[0].baseVAddr) + 0x9000;
if ((uptr->UserInit)(barbase, uptr->privData) < 0)
{
log_verbose(KERN_ERR "Initialization unsuccessful\n");
return NULL;
}
spin_lock_bh(&DmaLock);
/* Should inform the user of the errors !!!! */
result = descriptor_init(eptr->pdev, eptr);
if (result) {
/* At this point, handle has not been returned to the user.
* So, user refuses to prepare buffers. Will be trying again in
* the poll_routine. So, do not abort here.
*/
printk(KERN_ERR "Cannot create BD ring, will try again later.\n");
//return NULL;
}
/* Change the state of the engine, and increment the user count */
eptr->EngineState = USER_ASSIGNED;
dmaData->userCount ++ ;
/* Start the DMA engine */
if (Dma_BdRingStart(&(eptr->BdRing)) == XST_FAILURE) {
log_normal(KERN_ERR "DmaRegister: Could not start Dma channel\n");
return NULL;
}
printk("Now enabling interrupts\n");
Dma_mEngIntEnable(eptr);
spin_unlock_bh(&DmaLock);
log_verbose(KERN_INFO "Returning user handle %p\n", eptr);
return eptr;
}
3.DMA写函数
1 | xraw_dev_write (struct file *file, const char __user * buffer, size_t length, loff_t * offset) |
其中调用了1
DmaSetupTransmit(handle[0], 1, buffer, length)
ENGINE_TX:只实现了ufuncs.UserPutPkt = myPutTxPkt;(用来将packet buffer还给application-specific dirver,以便reuse,对应代码里面更新TxSync)
ENGINE_RX:实现了ufuncs.UserPutPkt = myPutRxPkt; 和ufuncs.UserGetPkt = myGetRxPkt;
即write对应的是handle[0],即ENGINE_TX发送。
