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分类： LINUX
2010-08-19 16:19:17
Include\asm-arm\arch-s3c2410\dma.h:
/* enum s3c2410_dma_loadst
*
* This represents the state of the DMA engine, wrt to the loaded / running
* transfers. Since we don't have any way of knowing exactly the state of
* the DMA transfers, we need to know the state to make decisions on wether
* we can
*
* S3C2410_DMA_NONE
*
* There are no buffers loaded (the channel should be inactive)
*
* S3C2410_DMA_1LOADED
*
* There is one buffer loaded, however it has not been confirmed to be
* loaded by the DMA engine. This may be because the channel is not
* yet running, or the DMA driver decided that it was too costly to
* sit and wait for it to happen.
*
* S3C2410_DMA_1RUNNING
*
* The buffer has been confirmed running, and not finisged
*
* S3C2410_DMA_1LOADED_1RUNNING
*
* There is a buffer waiting to be loaded by the DMA engine, and one
* currently running.
*/
enum s3c2410_dma_loadst {
S3C2410_DMALOAD_NONE,
S3C2410_DMALOAD_1LOADED,
S3C2410_DMALOAD_1RUNNING,
S3C2410_DMALOAD_1LOADED_1RUNNING,
};
各种装态注释的很明显了 , 我就不再罗索了 .
Channel 运行时会有一个正在传输的 buf, 一个已经加载的 buf, 还有很多等待加载的 buf.
我们来把这个函数中调用的函数也 逐个分析下 :
Arch\arm\plat-s3c24xx\dma.c:
/* s3c2410_dma_waitforload
*
* wait for the DMA engine to load a buffer, and update the state accordingly
*/
static int
s3c2410_dma_waitforload(struct s3c2410_dma_chan *chan, int line)
{
int timeout = chan->load_timeout; // 初始化时 load_timeout 被设成了 1 << 18
int took;
// 该函数只在 S3C2410_DMALOAD_1LOADED 状态下被调用
if (chan->load_state != S3C2410_DMALOAD_1LOADED) {
printk(KERN_ERR "dma%d: s3c2410_dma_waitforload() called in loadstate %d from line %d\n", chan->number, chan->load_state, line);
return 0;
}
if (chan->stats != NULL)
chan->stats->loads++; // 更新统计信息
while (--timeout > 0) {
// 获取还剩的传输量 , 左移 (32-20) 只是把 [21:20] 位移调 , 因为它仅和 0 比较 , 所以无需确切的数据
if ((dma_rdreg(chan, S3C2410_DMA_DSTAT) << (32-20)) != 0) {
took = chan->load_timeout - timeout; // 等待了这么长时间
// 保存统计信息 , 该函数更新最长 , 最短超时时间 , 并更新总超时时间
s3c2410_dma_stats_timeout(chan->stats, took);
switch (chan->load_state) {
case S3C2410_DMALOAD_1LOADED:
// 因为有数据在传输了 , 因此更新 channel 的状态 , 从这我们也能看到 , 一次只能有一个
//buf 被 load
chan->load_state = S3C2410_DMALOAD_1RUNNING;
break;
default:
printk(KERN_ERR "dma%d: unknown load_state in s3c2410_dma_waitforload() %d\n", chan->number, chan->load_state);
}
return 1;
}
}
if (chan->stats != NULL) {
chan->stats->timeout_failed++;
}
return 0;
}
该函数很简单 , 它等待已经 load 的 buf 被 start 传输 , 然后更新相关统计信息 , 也正因为 load 的 buf 被开始传输了 , 因此该函数完后 , 应该会有一个新的 buf 被 load. 至于原先 load 的 buf 是如何被 start 的 , 我们以后在看 .
接下来我们看 s3c2410_dma_canload 函数 :
Arch\arm\plat-s3c24xx\dma.c:
/* s3c2410_dma_canload
*
* work out if we can queue another buffer into the DMA engine
*/
static int
s3c2410_dma_canload(struct s3c2410_dma_chan *chan)
{
// 在这 2 个状态下是可以 load 的
if (chan->load_state == S3C2410_DMALOAD_NONE ||
chan->load_state == S3C2410_DMALOAD_1RUNNING)
return 1;
return 0;
}
跑完 s3c2410_dma_waitforload 后如果正确 , 则状态应该是 S3C2410_DMALOAD_1RUNNING, 所以这里就是可以加载了 , 那当然要看加载函数了
Arch\arm\plat-s3c24xx\dma.c:
/* 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 */
// 状态错误 , 只能有 1 个 loaded 的 buf
if (chan->load_state == S3C2410_DMALOAD_1LOADED) {
dmawarn("load_state is S3C2410_DMALOAD_1LOADED\n");
}
// 状态错误 , 只能有 1 个 loaded 的 buf
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...
*/
// 判断是否要自动加载后续的 buf, 如果有后续的 buf 则自动加载
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); // 写地址寄存器
// 不解释了 , 看寄存器说明吧
dma_wrreg(chan, S3C2410_DMA_DCON,
chan->dcon | reload | (buf->size/chan->xfer_unit));
chan->next = buf->next; // 更新链表
/* update the state of the channel */
// 更新状态
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;
}
该函数主要是把要传输的数据的 地址先存入寄存器中 , 等当前的传输完成后会根据时候 auto reload 的情况来确定是否开始这次的传输 .
OK, 到目前为止讲完了所有的 export 的函数 , 现在还剩下 dma 的操作函数和中断函数没讲了 , let’s go!
我们先看中断函数 , 该函数在一次传输完成后被调用
Arch\arm\plat-s3c24xx\dma.c:
static irqreturn_t
s3c2410_dma_irq(int irq, void *devpw)
{
struct s3c2410_dma_chan *chan = (struct s3c2410_dma_chan *)devpw;
struct s3c2410_dma_buf *buf;
buf = chan->curr; // 当前传输完毕的 buf
dbg_showchan(chan);
/* modify the channel state */
// 修改当前状态
switch (chan->load_state) {
case S3C2410_DMALOAD_1RUNNING:
/* TODO - if we are running only one buffer, we probably
* want to reload here, and then worry about the buffer
* callback */
chan->load_state = S3C2410_DMALOAD_NONE;
break;
case S3C2410_DMALOAD_1LOADED:
/* iirc, we should go back to NONE loaded here, we
* had a buffer, and it was never verified as being
* loaded.
*/
chan->load_state = S3C2410_DMALOAD_NONE;
break;
case S3C2410_DMALOAD_1LOADED_1RUNNING:
/* we'll worry about checking to see if another buffer is
* ready after we've called back the owner. This should
* ensure we do not wait around too long for the DMA
* engine to start the next transfer
*/
chan->load_state = S3C2410_DMALOAD_1LOADED;
break;
case S3C2410_DMALOAD_NONE:
printk(KERN_ERR "dma%d: IRQ with no loaded buffer?\n",
chan->number);
break;
default:
printk(KERN_ERR "dma%d: IRQ in invalid load_state %d\n",
chan->number, chan->load_state);
break;
}
if (buf != NULL) {
/* update the chain to make sure that if we load any more
* buffers when we call the callback function, things should
* work properly */
chan->curr = buf->next; // 更新传输的 buf
buf->next = NULL;
if (buf->magic != BUF_MAGIC) {
printk(KERN_ERR "dma%d: %s: buf %p incorrect magic\n",
chan->number, __FUNCTION__, buf);
return IRQ_HANDLED;
}
s3c2410_dma_buffdone(chan, buf, S3C2410_RES_OK); //buf 传输完成后的操作
/* free resouces */
s3c2410_dma_freebuf(buf); // 释放 buf, 我们看到传输前有申请 buf
} else {
}
/* only reload if the channel is still running... our buffer done
* routine may have altered the state by requesting the dma channel
* to stop or shutdown... */
/* todo: check that when the channel is shut-down from inside this
* function, we cope with unsetting reload, etc */
// 还有要传输的 buf, 则继续传输
if (chan->next != NULL && chan->state != S3C2410_DMA_IDLE) {
unsigned long flags;
switch (chan->load_state) {
case S3C2410_DMALOAD_1RUNNING:
/* don't need to do anything for this state */
break;
case S3C2410_DMALOAD_NONE:
/* can load buffer immediately */
break;
case S3C2410_DMALOAD_1LOADED:
if (s3c2410_dma_waitforload(chan, __LINE__) == 0) { // 等待被传输
/* flag error? */
printk(KERN_ERR "dma%d: timeout waiting for load (%s)\n",
chan->number, __FUNCTION__);
return IRQ_HANDLED;
}
break;
case S3C2410_DMALOAD_1LOADED_1RUNNING:
goto no_load;
default:
printk(KERN_ERR "dma%d: unknown load_state in irq, %d\n",
chan->number, chan->load_state);
return IRQ_HANDLED;
}
local_irq_save(flags);
s3c2410_dma_loadbuffer(chan, chan->next); // 加载下一个 buf
local_irq_restore(flags);
} else { // 所有的传输完成
s3c2410_dma_lastxfer(chan); // 完成处理工作
/* see if we can stop this channel.. */
if (chan->load_state == S3C2410_DMALOAD_NONE) {
pr_debug("dma%d: end of transfer, stopping channel (%ld)\n",
chan->number, jiffies);
s3c2410_dma_ctrl(chan->number | DMACH_LOW_LEVEL,
S3C2410_DMAOP_STOP); // 停止 dma 传输
}
}
no_load:
return IRQ_HANDLED;
}
我们看到当传输队列中还有 buf 要传输时 , 没有看到 start 的操作 , 这是为什么呢 ? 因为在 load 的时候我们分析过 , 如果后续还有 buf 要传输 , 则自动加载运行 , 所以这里没有必要手工 start.
s3c2410_dma_buffdone() 函数仅仅是调用前面注册的回调函数 , 这里不列出来了 .
s3c2410_dma_freebuf() 也很简单 , 就是把 buf 归还到缓冲池去 .
我们看下 s3c2410_dma_lastxfer
Arch\arm\plat-s3c24xx\dma.c:
/* s3c2410_dma_lastxfer
*
* called when the system is out of buffers, to ensure that the channel
* is prepared for shutdown.
*/
static inline void
s3c2410_dma_lastxfer(struct s3c2410_dma_chan *chan)
{
#if 0
pr_debug("dma%d: s3c2410_dma_lastxfer: load_state %d\n",
chan->number, chan->load_state);
#endif
switch (chan->load_state) {
case S3C2410_DMALOAD_NONE:
break;
case S3C2410_DMALOAD_1LOADED:
if (s3c2410_dma_waitforload(chan, __LINE__) == 0) { // 等待加载的 buf 被执行
/* flag error? */
printk(KERN_ERR "dma%d: timeout waiting for load (%s)\n",
chan->number, __FUNCTION__);
return;
}
break;
case S3C2410_DMALOAD_1LOADED_1RUNNING:
/* I belive in this case we do not have anything to do
* until the next buffer comes along, and we turn off the
* reload */
return;
default:
pr_debug("dma%d: lastxfer: unhandled load_state %d with no next\n",
chan->number, chan->load_state);
return;
}
/* hopefully this'll shut the damned thing up after the transfer... */
// 清楚自动加载标记 , 因为无后续要传输的 buf, 所以要清这个标记
dma_wrreg(chan, S3C2410_DMA_DCON, chan->dcon | S3C2410_DCON_NORELOAD);
}
很简单的一个函数 , 这里不多说了 .
好了 , 到这个该着中分析操作函数了 .
Arch\arm\plat-s3c24xx\dma.c:
/* s3c2410_dma_start
*
* start a dma channel going
*/
static int s3c2410_dma_start(struct s3c2410_dma_chan *chan)
{
unsigned long tmp;
unsigned long flags;
pr_debug("s3c2410_start_dma: channel=%d\n", chan->number);
local_irq_save(flags);
if (chan->state == S3C2410_DMA_RUNNING) { // 已经有 run 的了
pr_debug("s3c2410_start_dma: already running (%d)\n", chan->state);
local_irq_restore(flags);
return 0;
}
chan->state = S3C2410_DMA_RUNNING; // 更新状态
/* check wether there is anything to load, and if not, see
* if we can find anything to load
*/
if (chan->load_state == S3C2410_DMALOAD_NONE) { // 没有加载过 buf
if (chan->next == NULL) { // 没有 buf 要传送的
printk(KERN_ERR "dma%d: channel has nothing loaded\n",
chan->number);
chan->state = S3C2410_DMA_IDLE;
local_irq_restore(flags);
return -EINVAL;
}
s3c2410_dma_loadbuffer(chan, chan->next); // 加载 buf, 加载状态也会相应更新
}
dbg_showchan(chan);
/* enable the channel */
if (!chan->irq_enabled) {
enable_irq(chan->irq); // 使能中断
chan->irq_enabled = 1;
}
/* start the channel going */
// 启动 DMA 传输 ,
tmp = dma_rdreg(chan, S3C2410_DMA_DMASKTRIG);
tmp &= ~S3C2410_DMASKTRIG_STOP;
tmp |= S3C2410_DMASKTRIG_ON;
dma_wrreg(chan, S3C2410_DMA_DMASKTRIG, tmp);
pr_debug("dma%d: %08lx to DMASKTRIG\n", chan->number, tmp);
#if 0
/* the dma buffer loads should take care of clearing the AUTO
* reloading feature */
tmp = dma_rdreg(chan, S3C2410_DMA_DCON);
tmp &= ~S3C2410_DCON_NORELOAD;
dma_wrreg(chan, S3C2410_DMA_DCON, tmp);
#endif
s3c2410_dma_call_op(chan, S3C2410_DMAOP_START); // 调用注册的 op 回调函数
dbg_showchan(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 */
// 由于当前 load 的已经在运行了 , 因此如果还有要传输的 buf 则 load 进来
if (chan->next != NULL) {
if (chan->load_state == S3C2410_DMALOAD_1LOADED) {
// 等待该 buf 被运行 , 别忘了我们设了自动加载运行 .
if (s3c2410_dma_waitforload(chan, __LINE__) == 0) {
pr_debug("%s: buff not yet loaded, no more todo\n",
__FUNCTION__);
} else {
chan->load_state = S3C2410_DMALOAD_1RUNNING;
s3c2410_dma_loadbuffer(chan, chan->next); // 加载 buf
}
} else if (chan->load_state == S3C2410_DMALOAD_1RUNNING) {
s3c2410_dma_loadbuffer(chan, chan->next); // 加载 buf
}
}
local_irq_restore(flags);
return 0;
}
整个启动流程就这样完了 .
Arch\arm\plat-s3c24xx\dma.c:
static int s3c2410_dma_dostop(struct s3c2410_dma_chan *chan)
{
unsigned long flags;
unsigned long tmp;
pr_debug("%s:\n", __FUNCTION__);
dbg_showchan(chan);
local_irq_save(flags);
s3c2410_dma_call_op(chan, S3C2410_DMAOP_STOP); // 通知用户该操作
// 停止 DMA 传输
tmp = dma_rdreg(chan, S3C2410_DMA_DMASKTRIG);
tmp |= S3C2410_DMASKTRIG_STOP;
//tmp &= ~S3C2410_DMASKTRIG_ON;
dma_wrreg(chan, S3C2410_DMA_DMASKTRIG, tmp);
#if 0
/* should also clear interrupts, according to WinCE BSP */
tmp = dma_rdreg(chan, S3C2410_DMA_DCON);
tmp |= S3C2410_DCON_NORELOAD;
dma_wrreg(chan, S3C2410_DMA_DCON, tmp);
#endif
// 更新状态
/* should stop do this, or should we wait for flush? */
chan->state = S3C2410_DMA_IDLE;
chan->load_state = S3C2410_DMALOAD_NONE;
local_irq_restore(flags);
return 0;
}
该函数比较简单 , 接着看
Arch\arm\plat-s3c24xx\dma.c:
/* s3c2410_dma_flush
*
* stop the channel, and remove all current and pending transfers
*/
static int s3c2410_dma_flush(struct s3c2410_dma_chan *chan)
{
struct s3c2410_dma_buf *buf, *next;
unsigned long flags;
pr_debug("%s: chan %p (%d)\n", __FUNCTION__, chan, chan->number);
dbg_showchan(chan);
local_irq_save(flags);
if (chan->state != S3C2410_DMA_IDLE) {
pr_debug("%s: stopping channel...\n", __FUNCTION__ );
s3c2410_dma_ctrl(chan->number, S3C2410_DMAOP_STOP); // 停调传输
}
buf = chan->curr;
if (buf == NULL)
buf = chan->next;
chan->curr = chan->next = chan->end = NULL;
if (buf != NULL) {
for ( ; buf != NULL; buf = next) {
next = buf->next;
pr_debug("%s: free buffer %p, next %p\n",
__FUNCTION__, buf, buf->next);
s3c2410_dma_buffdone(chan, buf, S3C2410_RES_ABORT); // 通知用户中断了传输
s3c2410_dma_freebuf(buf); // 释放 buf
}
}
dbg_showregs(chan);
s3c2410_dma_waitforstop(chan);
#if 0
/* should also clear interrupts, according to WinCE BSP */
{
unsigned long tmp;
tmp = dma_rdreg(chan, S3C2410_DMA_DCON);
tmp |= S3C2410_DCON_NORELOAD;
dma_wrreg(chan, S3C2410_DMA_DCON, tmp);
}
#endif
dbg_showregs(chan);
local_irq_restore(flags);
return 0;
}
该函数的作用就是中断所有的传输 , 并把所有队列中等待传输的 buf 都清掉 .
Arch\arm\plat-s3c24xx\dma.c:
static int s3c2410_dma_started(struct s3c2410_dma_chan *chan)
{
unsigned long flags;
local_irq_save(flags);
dbg_showchan(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 */
// 看注释吧 , 不解释了
if (chan->next != NULL) {
if (chan->load_state == S3C2410_DMALOAD_1LOADED) {
if (s3c2410_dma_waitforload(chan, __LINE__) == 0) {
pr_debug("%s: buff not yet loaded, no more todo\n",
__FUNCTION__);
} else {
chan->load_state = S3C2410_DMALOAD_1RUNNING;
s3c2410_dma_loadbuffer(chan, chan->next);
}
} else if (chan->load_state == S3C2410_DMALOAD_1RUNNING) {
s3c2410_dma_loadbuffer(chan, chan->next);
}
}
local_irq_restore(flags);
return 0;
}
最后的这个函数就由大家自己分 析吧 .
从 s3c2410_dma_config 函数可以看出 , 该驱动只支持硬件请求模式 , 而从 s3c2410_dma_devconfig 函数可以看出 , 该驱动只支持设备和 memory 之间的 DMA 传输 .
至于如何使用的问题 , 可以去代码里搜一下哪些地方调用了 export 出来的函数就懂了 , 2410 的板子上 PCM 会用到 DMA 传输 , 使用流程为 :
s3c2410_dma_request ->
s3c2410_dma_devconfig ->
s3c2410_dma_config ->
s3c2410_dma_ctrl(prtd->params->channel, S3C2410_DMAOP_START);
当然一般还会注册回调函数的 .
到此为止整个 DMA 的操作流程都分析完了 , 希望对你有所帮助 ,
以后会写些 cache, mmu, write buffer 等方面的驱动分析 .
