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s3c2410的dma操作的一般步驟

s3c2410的dma操作的一般步驟

一般的，在s3c2440中，要想進行dma傳輸，需要一下七個步驟：

一：
/* s3c2410_request_dma
*
* get control of an dma channel
*/
int s3c2410_dma_request(unsigned int channel,
                        struct s3c2410_dma_client *client,
                        void *dev)

s3c2410_dma_client的定義為：
struct s3c2410_dma_client {
    char    *name;
};

二：
/* DMA configuration for each channel
*
* DISRCC -> source of the DMA (AHB(系統總線),APB(外圍總線))
* DISRC  -> source address of the DMA
* DIDSTC -> destination of the DMA (AHB,APD)
* DIDST  -> destination address of the DMA
*/
/* s3c2410_dma_config
*
* xfersize:     size of unit in bytes (1,2,4)
* dcon:         base value of the DCONx register
*/

int s3c2410_dma_config(dmach_t channel,
                       int xferunit,
                       int dcon)
根據xferunit以及dcon設置通道的控制寄存器DCONx
xferunit為每次傳輸的數據大小：0:byte 1:half word 2:word

每個 DMA 通道都有 9 個控制寄存器（4 個通道 DMA 控制器共計 36 個寄存器）。
6 個寄存器用來控制 DMA 傳輸，其他三個監視 DMA 控制器的狀態。這些寄存器的詳細情況如下：
（1）DMA 初始源寄存器(DISRC)
（2）DMA初始源控制寄存器(DISRCC)
（3）DMA初始目的寄存器(DIDST)
（4）DMA初始目的控制寄存器(DIDSTC)
（5）DMA控制寄存器(DCON)
（6）DMA狀態寄存器（DSTAT）
（7）DMA當前源寄存器(DCSRC)
（8）DMA當前目的寄存器(DCDST)
（9）DMA屏蔽觸發寄存器(DMASKTRIG)

三：
int s3c2410_dma_set_buffdone_fn(dmach_t channel, s3c2410_dma_cbfn_t rtn)
{
    struct s3c2410_dma_chan *chan = lookup_dma_channel(channel);
    if (chan == NULL)
        return -EINVAL;
    pr_debug("%s: chan=%p, callback rtn=%p\n", __func__, chan, rtn);
    chan->callback_fn = rtn;
    return 0;
}
設置相應的dma通道完成一次dma傳輸后的回調函數，也即是s3c2410_dma_enqueue完成后會調用的函數

回調函數應具有一下格式：
/* s3c2410_dma_cbfn_t
*
* buffer callback routine type
*/
typedef void (*s3c2410_dma_cbfn_t)(struct s3c2410_dma_chan *,
                                   void *buf, int size,
                                   enum s3c2410_dma_buffresult result);

buf可以傳遞一些有用的數據，在uda1314的驅動中，傳遞的是audio_buf_t結構體

四：
int s3c2410_dma_setflags(dmach_t channel, unsigned int flags)
{
    struct s3c2410_dma_chan *chan = lookup_dma_channel(channel);
    if (chan == NULL)
        return -EINVAL;
    pr_debug("%s: chan=%p, flags=%08x\n", __func__, chan, flags);
    chan->flags = flags;
    return 0;
}

五：
/* s3c2410_dma_devconfig
*
* configure the dma source/destination hardware type and address
*
* 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=source is AHB, 1=source is APB
*
* devaddr:   physical address of the source
*/

int s3c2410_dma_devconfig(int channel,
                          enum s3c2410_dmasrc source,
                          int hwcfg,
                          unsigned long devaddr)

六：
/*
* Allocate memory for a coherent(連續的) mapping.
*/
void *dma_alloc_coherent(struct device *dev,size_t size,dma_addr_t *dma_handle,int flag)
如:
void *pLogicAddr = NULL;/*邏輯地址*/
dma_addr_t pBusAddr = NULL;/*總線地址(實際物理地址)*/
pLogicAddr = dma_alloc_coherent(NULL, 480*640, &pBusAddr, GFP_KERNEL | GFP_DMA);

該函數實際獲得兩個地址，
1、函數的返回值是一個void *，代表緩沖區的內核虛擬地址
2、相關的總線地址，保存在dma_handle中

dma關心的是總線地址。
物理地址與總線地址
1) 物理地址是與CPU相關的。在CPU的地址信號線上產生的就是物理地址。在程序指令中的虛擬地址經過段映射和頁面映射后，就生成了物理地址，這個物理地址被放到CPU的地址線上。
2) 總線地址，顧名思義，是與總線相關的，就是總線的地址線或在地址周期上產生的信號。外設使用的是總線地址。
3) 物理地址與總線地址之間的關系由系統的設計決定的。在x86平臺上，物理地址與PCI總線地址是相同的。在其他平臺上，也許會有某種轉換，通常是線性的轉換。

七：
/* s3c2410_dma_enqueue
*
* queue an given buffer for dma transfer.
*
* id         the device driver's id information for this buffer
* data       the physical address of the buffer data
* size       the size of the buffer in bytes
*
* If the channel is not running, then the flag S3C2410_DMAF_AUTOSTART
* is checked, and if set, the channel is started. If this flag isn't set,
* then an error will be returned.
*
* It is possible to queue more than one DMA buffer onto a channel at
* once, and the code will deal with the re-loading of the next buffer
* when necessary.
*/

int s3c2410_dma_enqueue(unsigned int channel, void *id,dma_addr_t data, int size)
將dma_alloc_coherent中得到的dmaphys傳遞給s3c2410_dma_enqueue.
s3c2410_dma_enqueue提交一次dma請求，當dma通道可用的時候通過s3c2410_dma_loadbuffer開始一次傳輸，傳輸完成后會產生irq中斷。其dma的中斷服務函數中會繼續啟動dma請求隊列中的請求，傳輸剩下的數據。

/* s3c2410_dma_buffdone
*
* small wrapper to check if callback routine needs to be called, and
* if so, call it
*/
static inline void s3c2410_dma_buffdone(struct s3c2410_dma_chan *chan, struct s3c2410_dma_buf *buf,
                                         enum s3c2410_dma_buffresult result)
{
    if (chan->callback_fn != NULL) {
        (chan->callback_fn)(chan, buf->id, buf->size, result);
    }
}
其中 s3c2410_dma_irq 會調用 s3c2410_dma_buffdone;
static irqreturn_t s3c2410_dma_irq(int irq, void *devpw)

/* s3c2410_request_dma
*
* get control of an dma channel
*/
int s3c2410_dma_request(unsigned int channel,
                        struct s3c2410_dma_client *client,
                        void *dev)
{
    struct s3c2410_dma_chan *chan;
    unsigned long flags;
    int err;

    pr_debug("dma%d: s3c2410_request_dma: client=%s, dev=%p\n",
         channel, client->name, dev);

    local_irq_save(flags);
    chan = s3c2410_dma_map_channel(channel);
    if (chan == NULL) {
        local_irq_restore(flags);
        return -EBUSY;
    }
    dbg_showchan(chan);
    chan->client = client;
    chan->in_use = 1;
    if (!chan->irq_claimed) {
        pr_debug("dma%d: %s : requesting irq %d\n",
             channel, __func__, chan->irq);

        chan->irq_claimed = 1;
        local_irq_restore(flags);
        err = request_irq(chan->irq, s3c2410_dma_irq, IRQF_DISABLED,
                  client->name, (void *)chan);
        local_irq_save(flags);
        if (err) {
            chan->in_use = 0;
            chan->irq_claimed = 0;
            local_irq_restore(flags);
            printk(KERN_ERR "%s: cannot get IRQ %d for DMA %d\n",
                   client->name, chan->irq, chan->number);
            return err;
        }
        chan->irq_enabled = 1;
    }
    local_irq_restore(flags);
    /* need to setup */
    pr_debug("%s: channel initialised, %p\n", __func__, chan);
    return chan->number | DMACH_LOW_LEVEL;
}

/**
*    request_irq - allocate an interrupt line
*    @irq: Interrupt line to allocate
*    @handler: Function to be called when the IRQ occurs
*    @irqflags: Interrupt type flags
*    @devname: An ascii name for the claiming device
*    @dev_id: A cookie passed back to the handler function
*
*    This call allocates interrupt resources and enables the
*    interrupt line and IRQ handling. From the point this
*    call is made your handler function may be invoked. Since
*    your handler function must clear any interrupt the board
*    raises, you must take care both to initialise your hardware
*    and to set up the interrupt handler in the right order.
*
*    Dev_id must be globally unique. Normally the address of the
*    device data structure is used as the cookie. Since the handler
*    receives this value it makes sense to use it.
*
*    If your interrupt is shared you must pass a non NULL dev_id
*    as this is required when freeing the interrupt.
*
*    Flags:
*
*    IRQF_SHARED        Interrupt is shared
*    IRQF_DISABLED    Disable local interrupts while processing
*    IRQF_SAMPLE_RANDOM    The interrupt can be used for entropy
*
*/
int request_irq(unsigned int irq, irq_handler_t handler,
        unsigned long irqflags, const char *devname, void *dev_id)
{
    struct irqaction *action;
    int retval;
    action = kmalloc(sizeof(struct irqaction), GFP_ATOMIC);
    if (!action)
        return -ENOMEM;
    action->handler = handler;
    action->flags = irqflags;
    cpus_clear(action->mask);
    action->name = devname;
    action->next = NULL;
    action->dev_id = dev_id;

    select_smp_affinity(irq);

    retval = setup_irq(irq, action);
    if (retval)
        kfree(action);

    return retval;
}

/* s3c2410_dma_loadbuffer
*
* load a buffer, and update the channel state
*/
static inline int s3c2410_dma_loadbuffer(struct s3c2410_dma_chan *chan,
                                            struct s3c2410_dma_buf *buf)
{
    unsigned long reload;
    pr_debug("s3c2410_chan_loadbuffer: loading buff %p (0x%08lx,0x%06x)\n",
         buf, (unsigned long)buf->data, buf->size);
    if (buf == NULL) {
        dmawarn("buffer is NULL\n");
        return -EINVAL;
    }
    /* check the state of the channel before we do anything */
    if (chan->load_state == S3C2410_DMALOAD_1LOADED) {
        dmawarn("load_state is S3C2410_DMALOAD_1LOADED\n");
    }
    if (chan->load_state == S3C2410_DMALOAD_1LOADED_1RUNNING) {
        dmawarn("state is S3C2410_DMALOAD_1LOADED_1RUNNING\n");
    }
    /* it would seem sensible if we are the last buffer to not bother
     * with the auto-reload bit, so that the DMA engine will not try
     * and load another transfer after this one has finished

     */
    if (chan->load_state == S3C2410_DMALOAD_NONE) {
        pr_debug("load_state is none, checking for noreload (next=%p)\n",
             buf->next);
        reload = (buf->next == NULL) ? S3C2410_DCON_NORELOAD : 0;
    } else {
        //pr_debug("load_state is %d => autoreload\n", chan->load_state);
        reload = S3C2410_DCON_AUTORELOAD;
    }

    if ((buf->data & 0xf0000000) != 0x30000000) {
        dmawarn("dmaload: buffer is %p\n", (void *)buf->data);
    }

    writel(buf->data, chan->addr_reg);

    dma_wrreg(chan, S3C2410_DMA_DCON,
          chan->dcon | reload | (buf->size/chan->xfer_unit));

    chan->next = buf->next;

    /* update the state of the channel */

    switch (chan->load_state) {
    case S3C2410_DMALOAD_NONE:
        chan->load_state = S3C2410_DMALOAD_1LOADED;
        break;

    case S3C2410_DMALOAD_1RUNNING:
        chan->load_state = S3C2410_DMALOAD_1LOADED_1RUNNING;
        break;

    default:
        dmawarn("dmaload: unknown state %d in loadbuffer\n",
            chan->load_state);
        break;
    }
    return 0;
}

＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝
一些相關函數的說明。供自己日后參考。
--------------------------------------------------------------------------------------
int __init s3c24xx_dma_init_map(struct s3c24xx_dma_selection *sel)
初始化全局變量dma_sel結構，在此函數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;
這幾條語句，為什么用memcpy初始化為了dma_sel，而又要用再分配的nmap結構去給dma_sel賦值。其答案是為了保險，因為dma_sel 中的map成員是個指針。對指針的操作是要很小心的。這里在此函數中重新定義一個指針變量，并指向它，就是為了防止別處定義的指針被撤消而造成越界訪問。其實我認為這沒有必要的。

dma_sel的定義為struct s3c24xx_dma_selection dma_sel;
而struct s3c24xx_dma_selection的定義為
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)
此函數功能是： turn the virtual channel number into a real, and un-used hardware channel.完成DMA通道的虛實映射
在s3c2440_dma_mappings數組中查找相應channel對應的通道(0--4,有效未使用),并將映射關系記入dma_chan_map[channel]數組中。

---------------------------------------------------------------------------------------------------------
static int __init s3c2410_init_dma(void)
用于初始化s3c2410_dma_chan結構，并完成地址映射。

-----------------------------------------------------------------------------------------------------------
static struct s3c2410_dma_chan *lookup_dma_channel(unsigned int channel)
DMA通道虛實轉換

-----------------------------------------------------------------------------------------------------------
int s3c2410_dma_request(unsigned int channel,
            struct s3c2410_dma_client *client,
            void *dev)
通過s3c2410_dma_map_channel函數找到channel對應的通道，并設置相應的通道狀態，申請中斷
-----------------------------------------------------------------------------------------------------------

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)
根據xferunit設置通道的控制寄存器
--------------------------------------------------------------------------------------------------------------
int s3c2410_dma_setflags(dmach_t channel, unsigned int flags)
根據flags設置通道的flags
--------------------------------------------------------------------------------------------------------------

int s3c2410_dma_ctrl(dmach_t channel, enum s3c2410_chan_op op);

0

posted on 2012-12-04 08:58 天下閱讀(830) 評論(0) 編輯收藏引用所屬分類: kernel & Driver

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