关于2.6.20中的dma的

一些相关函数的说明。供自己日后参考。
--------------------------------------------------------------------------------------
int __init s3c24xx_dma_init_map(struct s3c24xx_dma_selection *sel)
初始化全局变量dma_sel结构，在此函数中大家可能疑惑的是
    nmap = kmalloc(map_sz, GFP_KERNEL);
    if (nmap == NULL)
        return -ENOMEM;

    memcpy(nmap, sel->map, map_sz);
    memcpy(&dma_sel, sel, sizeof(*sel));

    dma_sel.map = nmap;
这 几条语句，为什么用memcpy初始化为了dma_sel，而又要用再分配的nmap结构去给dma_sel赋值。其答案是为了保险，因为dma_sel 中的map成员是个指针。对指针的操作是要很小心的。这里在此函数中重新定义一个指针变量，并指向它，就是为了防止别处定义的指针被撤消而造成越界。其实我认为这没有必要的。

dma_sel的定义为struct s3c24xx_dma_selection dma_sel;
而struct s3c24xx_dma_selection的定义为
struct s3c24xx_dma_selection {
    struct s3c24xx_dma_map    *map;
    unsigned long         map_size;
    unsigned long         dcon_mask;

    void    (*select)(struct s3c2410_dma_chan *chan,
              struct s3c24xx_dma_map *map);
};


--------------------------------------------------------------------------------------------------------
struct s3c2410_dma_chan *s3c2410_dma_map_channel(int channel)
此函数是： turn the virtual channel number into a real, and un-used hardware channel.完成通道的虚实映射
在s3c2440_dma_mappings数组中查找相应channel对应的通道(0--4,有效未使用),并将映射关系记入dma_chan_map[channel]数组中。


---------------------------------------------------------------------------------------------------------
static int __init s3c2410_init_dma(void)
用于初始化s3c2410_dma_chan结构，并完成映射。

-----------------------------------------------------------------------------------------------------------
static struct s3c2410_dma_chan *lookup_dma_channel(unsigned int channel)
DMA通道虚实转换

-----------------------------------------------------------------------------------------------------------
int s3c2410_dma_request(unsigned int channel,
            struct s3c2410_dma_client *client,
            void *dev)
通过s3c2410_dma_map_channel函数找到channel对应的通道，并相应的通道状态，申请中断
-----------------------------------------------------------------------------------------------------------

int s3c2410_dma_started(struct s3c2410_dma_chan *chan)
    /* if we've only loaded one buffer onto the channel, then chec
     * to see if we have another, and if so, try and load it so when
     * the first buffer is finished, the new one will be loaded onto
    * the channel */
-----------------------------------------------------------------------------------------------------------
int s3c2410_dma_free(dmach_t channel, struct s3c2410_dma_client *client)
/* s3c2410_dma_free
 *
 * release the given channel back to the system, will stop and flush
 * any outstanding transfers, and ensure the channel is ready for the
 * next claimant.
 *
 * Note, although a warning is currently printed if the freeing client
 * info is not the same as the registrant's client info, the free is still
 * allowed to go through.
*/

--------------------------------------------------------------------------------------------------------------
static int s3c2410_dma_flush(struct s3c2410_dma_chan *chan)
 * stop the channel, and remove all current and pending transfers

--------------------------------------------------------------------------------------------------------------
int s3c2410_dma_config(dmach_t channel,
               int xferunit,
               int dcon)
根据xferunit设置通道的控制寄存器
--------------------------------------------------------------------------------------------------------------
int s3c2410_dma_setflags(dmach_t channel, unsigned int flags)
根据flags设置通道的flags
--------------------------------------------------------------------------------------------------------------
int s3c2410_dma_devconfig(int channel,
              enum s3c2410_dmasrc source,
              int hwcfg,
              unsigned long devaddr)
参数意义：
 * source:    S3C2410_DMASRC_HW: source is hardware
 *            S3C2410_DMASRC_MEM: source is memory
 *
 * hwcfg:     the value for xxxSTCn register,
 *            bit 0: 0=increment pointer, 1=leave pointer
 *            bit 1: 0=soucre is AHB, 1=soucre is APB
 *
 * devaddr:   physical address of the source

如果source为S3C2410_DMASRC_HW(外设), 配置它的S3C2410_DMA_DISRCC,S3C2410_DMA_DISRC,S3C2410_DMA_DIDSTC
如果source为S3C2410_DMASRC_MEM(内存),配置它的S3C2410_DMA_DISRCC,S3C2410_DMA_DIDST,S3C2410_DMA_DIDSTC
由此可见，地址方面，只配置涉及外设的地址

----------------------------------------------------------------------------------------------------------------