这是我的第一篇文章，所以如果有任何错误，请告诉我。
我的目标是让大约 150MB 的数据从 KERNEL 传输到用户空间。[这是因为我正在 OMAP l138 上为 DMA 设备构建驱动程序，以在 DMA DEVICE 和 FPGA 之间传输和接收数据]
- 现在在 LINUX 内核中，我使用 dma_alloc_coherent 分配 VARIABLE 大小的 BUFFER
- 然后我将此缓冲区的物理地址传递给用户空间作为用户空间的 OFFSET 参数，用于从用户空间调用 mmap。
- 然后从用户空间向内核复制和读取数据
此逻辑工作正常，直到缓冲区大小为 4096。高于 4k 时 mmap 失败并返回“MAP_FAILED”
static int driver_mmap(struct file *f, struct vm_area_struct *vma)
{
u32bit ret;
u32bit size = (vma->vm_end)-(vma->vm_start);
vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
if (size > (NUM_PAGE*PAGE_SIZE)){
return(-1);
}
if ((ret = remap_pfn_range(vma,vma->vm_start,
(virt_to_phys((void *)krnl_area) >> PAGE_SHIFT),
size,vma->vm_page_prot)) < 0)
{
return ret;
}
printk("\nDVR:The MMAP returned %x to USER SAPCE \n",ret);
return 0;
}
//MMAP STEP 1
dmasrc_ptr = dma_alloc_coherent( NULL ,GLOBAL_BUFFER_SIZE , &dmasrc ,0);
if( !dmasrc_ptr ) {
printk(KERN_INFO "DMA_ALLOC_FAILED for the source buffer ...\n");
return -ENOMEM;
}else{
printk( "\n--->The address of SRC is %x..\n",dmasrc_ptr);
}
temp_source=dmasrc_ptr;
//MMAP STEP 2
// Round the allocated KERNEL MEMORY to the page bondary
krnl_area=(int *)((((unsigned long)dmasrc_ptr) + PAGE_SIZE - 1)&PAGE_MASK);
printk(KERN_CRIT "DVR:The KERNEL VIRTUAL ADDRS is %x..\n",krnl_area);
//MMAP STEP 3
// Marking the PAGES as RESERVED
for (i = 0; i < (NUM_PAGE * PAGE_SIZE); i+= PAGE_SIZE) {
SetPageReserved(virt_to_page(((unsigned long)krnl_area) + i));
//Application code part
while(1){
fflush(stdin);
fflush(stdout);
printf("\n\n\n----------------------------------------------------\n");
printf("USR:Please enter your requirement ");
printf("\n----------------------------------------------------\n");
printf("\t1----->GET_UPP_OFFSET\n");
printf("\t2----->UPP_MMAP_CALL\n");
printf("\t3----->IOCTL_UPP_WRITE\n");
printf("\t4----->IOCTL_UPP_READ\n");
printf("\n");
scanf("%d",&option);
printf("\nThe OPTION is %d..\n",option);
printf("\n");
switch(option){
case 1 :
{
offset=0;
ret = ioctl(dev_FD ,IOCTL_UPP_START, &info);
if (ret < 0) {
printf("dma buffer info ioctl failed\n");
}
offset = info.var;
printf("THE ADDRESS WE GOT IS %X..\n",offset);
}
break;
case 2 :
{
printf("THE OFFSET is %X..\n",offset);
mmap_Ptr= mmap(0,BUFFER_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, dev_FD, 0);
if (mmap_Ptr == MAP_FAILED){
printf("USR[UPP] :MMAP FAiled \n\n");
close(dev_FD);
exit(-1);
}
printf("THE MMAP address is %X..\n",mmap_Ptr);
}
break;
case 3:
{
struct upp_struct user_local_struct;
printf("\n***************************************************\n");
for (i = 0; i <(1024);i++) {
*(mmap_Ptr+i)=test_var;
printf("WR:%X ",*(mmap_Ptr+i));
//test_var++;
}
ioctl(dev_FD , IOCTL_UPP_WRITE ,&user_local_struct);
printf("\n***************************************************\n\n\n");
for(i=0;i<20402;i++){
//NOP
}
//test_var=0x00;
}
break;
case 4:
{
struct upp_struct user_local_struct;
ioctl(dev_FD , IOCTL_UPP_READ,&user_local_struct);
for(i=0;i<20402;i++){
//NOP
}
printf("\n***************************************************\n");
for (i = 0; i <(1024);i++) {
printf("RD:%X",*(mmap_Ptr+i));
}
printf("\n***************************************************\n\n\n");
}
break;
default:
{
printf("USR:You have entered an wrong option \n");
printf("\nUSR:CLosing the FILE ENTERIES ...\n");
munmap(mmap_Ptr,BUFFER_SIZE);
free(source_ptr);
free(dest_ptr);
close(dev_FD);
exit(0);
}
break;
} //END OF SWITCH LOOP
} //END OF WHILE LOOP