自娱自乐9之Linux DMA使用1（三星平台DMA分析）
和以前一样，我不说dma基础知识，你可以看看ldd3
这次我说的是三星平台的dma，不是三星的某款芯片的dma使用。这主要得益于三星公司统一了接口。比如我后有的例子是在s3c2440上做的但是我是参考s3c64xx的spi驱动。
当然内核还是linux-3.2.36，我们看dma-ops.h
/* arch/arm/plat-samsung/include/plat/dma-ops.h
*
* Copyright (c) 2011 Samsung Electronics Co., Ltd.
* http://www.samsung.com
*
* Samsung DMA support
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#ifndef __SAMSUNG_DMA_OPS_H_
#define __SAMSUNG_DMA_OPS_H_ __FILE__
#include <linux/dmaengine.h>
struct samsung_dma_prep_info {
enum dma_transaction_type cap;//dma处理类型
enum dma_data_direction direction;//dma传输方向
dma_addr_t buf;//内存地址
unsigned long period;//
unsigned long len;//buf长度,sizeof(buf) * width，width在下面struct samsung_dma_info
/*
.c中调用
int len = (info->cap == DMA_CYCLIC) ? info->period : info->len;
...
我不是太清楚period和len区别
*/
void (*fp)(void *data);//dma中断时会调用，一般作为dma传输完成的接口
void *fp_param;//传入上面fp的参数
};
struct samsung_dma_info {
enum dma_transaction_type cap;//dma处理类型
/*
if (info->cap == DMA_CYCLIC)
s3c2410_dma_setflags(dma_ch, S3C2410_DMAF_CIRCULAR);//chan->flags设置
这个可能和芯片有点关系
我的plat-s3c24xx中，通道请求函数
if (chan->flags & S3C2410_DMAF_AUTOSTART) {//如果设置为自动运行，就调用start函数
s3c2410_dma_ctrl(chan->number | DMACH_LOW_LEVEL,
S3C2410_DMAOP_START);
}
没有判断S3C2410_DMAF_CIRCULAR标志
*/
enum dma_data_direction direction;//dma传输方向
enum dma_slave_buswidth width;//要传输的数据宽度，就是（字节、半字、字）
dma_addr_t fifo;//外设地址
struct s3c2410_dma_client *client;
/*
struct s3c2410_dma_client {
char *name;
};
就是一个name,你申请通道时命名就可以了，主要dma中断注册是用、free通道时判断
是不是正确通道
*/
};
struct samsung_dma_ops {
unsigned (*request)(enum dma_ch ch, struct samsung_dma_info *info);//请求会有些限制
//1.总是认为我们的外围设备是一个固定的地址
//2.总是认为我们的内存地址增加
//3.硬件触发
//4.所有传输完成产生中断
//上面这个从数据手册上看是可以设的，但是三星写的驱动代码没有选的可能
int (*release)(unsigned ch, struct s3c2410_dma_client *client);//释放
int (*prepare)(unsigned ch, struct samsung_dma_prep_info *info);//准备
//准备会把内存数据加入链表中，如果有数据在传输，会打开再加载开关
int (*trigger)(unsigned ch);//触发
int (*started)(unsigned ch);//再次开始，实际就是再次载入数据
int (*flush)(unsigned ch);//清除通道数据
int (*stop)(unsigned ch);//停止
};
extern void *samsung_dmadev_get_ops(void);
extern void *s3c_dma_get_ops(void);
//去获取一个struct samsung_dma_ops全局变量，
//然后调用驱动，这个倒是给我们提供了一种驱动之间调用的方法
static inline void *__samsung_dma_get_ops(void)
{
if (samsung_dma_is_dmadev())
return samsung_dmadev_get_ops();
else
return s3c_dma_get_ops();
}
/*
* samsung_dma_get_ops
* get the set of samsung dma operations
*/
//在驱动中调用这个
#define samsung_dma_get_ops() __samsung_dma_get_ops()
#endif /* __SAMSUNG_DMA_OPS_H_ */
如果你只是想看看应用接口，你可以在此打住，直接看《自娱自乐10》中dma使用的例子，增加你的理解。
如果你和我一样死脑筋，你可以看看下面的源码分析：主要有三个文件
下面这个文件，看的时候不要纠结，主要是为第二个通道使用的，知道就行。
/* linux/arch/arm/plat-samsung/dma.c * * Copyright (c) 2003-2009 Simtec Electronics * Ben Dooks <[email protected]> * http://armlinux.simtec.co.uk/ * * S3C DMA core * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. */ struct s3c2410_dma_buf; /* struct s3c2410_dma_buf { struct s3c2410_dma_buf *next; int magic; // magic int size; // buffer size in bytes dma_addr_t data; // start of DMA data dma_addr_t ptr; // where the DMA got to [1] void *id; // client's id }; */ #include <linux/kernel.h> #include <linux/module.h> #include <linux/errno.h> #include <mach/dma.h> #include <mach/irqs.h> /* dma channel state information */ struct s3c2410_dma_chan s3c2410_chans[S3C_DMA_CHANNELS]; struct s3c2410_dma_chan *s3c_dma_chan_map[DMACH_MAX]; /* s3c_dma_lookup_channel * * change the dma channel number given into a real dma channel id */ //查找对应通道的struct s3c2410_dma_chan //这个通道不是dma每个通道，是指外设对应的。 struct s3c2410_dma_chan *s3c_dma_lookup_channel(unsigned int channel) { if (channel & DMACH_LOW_LEVEL) return &s3c2410_chans[channel & ~DMACH_LOW_LEVEL]; else return s3c_dma_chan_map[channel]; } /* do we need to protect the settings of the fields from * irq? */ int s3c2410_dma_set_opfn(enum dma_ch channel, s3c2410_dma_opfn_t rtn) { struct s3c2410_dma_chan *chan = s3c_dma_lookup_channel(channel); if (chan == NULL) return -EINVAL; pr_debug("%s: chan=%p, op rtn=%p\n", __func__, chan, rtn); chan->op_fn = rtn; //从下面可以看出在开始和结束时会调用这个函数 return 0; } EXPORT_SYMBOL(s3c2410_dma_set_opfn); int s3c2410_dma_set_buffdone_fn(enum dma_ch channel, s3c2410_dma_cbfn_t rtn) { struct s3c2410_dma_chan *chan = s3c_dma_lookup_channel(channel); if (chan == NULL) return -EINVAL; pr_debug("%s: chan=%p, callback rtn=%p\n", __func__, chan, rtn); //在s3c2410_dma_flush和中断函数中调用 chan->callback_fn = rtn; return 0; } EXPORT_SYMBOL(s3c2410_dma_set_buffdone_fn); //设置标志 int s3c2410_dma_setflags(enum dma_ch channel, unsigned int flags) { struct s3c2410_dma_chan *chan = s3c_dma_lookup_channel(channel); if (chan == NULL) return -EINVAL; chan->flags = flags; return 0; } EXPORT_SYMBOL(s3c2410_dma_setflags);
下面是plat-s3c24xx中的，应该只适用s3c24xx芯片
文件有点大，我提供一个看的方法
1. 看init函数。
2. 看request函数。
3. 看s3c2410_dma_ctrl，里面有停止、开始等。
4. 看中断函数。
5. 看电源管理。
/* linux/arch/arm/plat-s3c24xx/dma.c * * Copyright 2003-2006 Simtec Electronics * Ben Dooks <[email protected]> * * S3C2410 DMA core * * http://armlinux.simtec.co.uk/ * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. */ #ifdef CONFIG_S3C2410_DMA_DEBUG #define DEBUG #endif #include <linux/module.h> #include <linux/init.h> #include <linux/sched.h> #include <linux/spinlock.h> #include <linux/interrupt.h> #include <linux/syscore_ops.h> #include <linux/slab.h> #include <linux/errno.h> #include <linux/io.h> #include <asm/system.h> #include <asm/irq.h> #include <mach/hardware.h> #include <mach/dma.h> #include <mach/map.h> #include <plat/dma-s3c24xx.h> #include <plat/regs-dma.h> /* io map for dma */ static void __iomem *dma_base; static struct kmem_cache *dma_kmem; static int dma_channels; static struct s3c24xx_dma_selection dma_sel; //调试功能就不看了 /* debugging functions */ #define BUF_MAGIC (0xcafebabe) #define dmawarn(fmt...) printk(KERN_DEBUG fmt) #define dma_regaddr(chan, reg) ((chan)->regs + (reg)) #if 1 #define dma_wrreg(chan, reg, val) writel((val), (chan)->regs + (reg)) #else static inline void dma_wrreg(struct s3c2410_dma_chan *chan, int reg, unsigned long val) { pr_debug("writing %08x to register %08x\n",(unsigned int)val,reg); writel(val, dma_regaddr(chan, reg)); } #endif #define dma_rdreg(chan, reg) readl((chan)->regs + (reg)) /* captured register state for debug */ struct s3c2410_dma_regstate { unsigned long dcsrc; //源 unsigned long disrc; //目标 unsigned long dstat; //状态 unsigned long dcon; //配置 unsigned long dmsktrig; //触发屏蔽 }; //下面还是调试，不看了 #ifdef CONFIG_S3C2410_DMA_DEBUG /* dmadbg_showregs * * simple debug routine to print the current state of the dma registers */ static void dmadbg_capture(struct s3c2410_dma_chan *chan, struct s3c2410_dma_regstate *regs) { regs->dcsrc = dma_rdreg(chan, S3C2410_DMA_DCSRC); regs->disrc = dma_rdreg(chan, S3C2410_DMA_DISRC); regs->dstat = dma_rdreg(chan, S3C2410_DMA_DSTAT); regs->dcon = dma_rdreg(chan, S3C2410_DMA_DCON); regs->dmsktrig = dma_rdreg(chan, S3C2410_DMA_DMASKTRIG); } static void dmadbg_dumpregs(const char *fname, int line, struct s3c2410_dma_chan *chan, struct s3c2410_dma_regstate *regs) { printk(KERN_DEBUG "dma%d: %s:%d: DCSRC=%08lx, DISRC=%08lx, DSTAT=%08lx DMT=%02lx, DCON=%08lx\n", chan->number, fname, line, regs->dcsrc, regs->disrc, regs->dstat, regs->dmsktrig, regs->dcon); } static void dmadbg_showchan(const char *fname, int line, struct s3c2410_dma_chan *chan) { struct s3c2410_dma_regstate state; dmadbg_capture(chan, &state); printk(KERN_DEBUG "dma%d: %s:%d: ls=%d, cur=%p, %p %p\n", chan->number, fname, line, chan->load_state, chan->curr, chan->next, chan->end); dmadbg_dumpregs(fname, line, chan, &state); } static void dmadbg_showregs(const char *fname, int line, struct s3c2410_dma_chan *chan) { struct s3c2410_dma_regstate state; dmadbg_capture(chan, &state); dmadbg_dumpregs(fname, line, chan, &state); } #define dbg_showregs(chan) dmadbg_showregs(__func__, __LINE__, (chan)) #define dbg_showchan(chan) dmadbg_showchan(__func__, __LINE__, (chan)) #else #define dbg_showregs(chan) do { } while(0) #define dbg_showchan(chan) do { } while(0) #endif /* CONFIG_S3C2410_DMA_DEBUG */ /* s3c2410_dma_stats_timeout * * Update DMA stats from timeout info */ //记录dma传输用时 static void s3c2410_dma_stats_timeout(struct s3c2410_dma_stats *stats, int val) { if (stats == NULL) return; if (val > stats->timeout_longest) stats->timeout_longest = val; if (val < stats->timeout_shortest) stats->timeout_shortest = val; stats->timeout_avg += val; } /* s3c2410_dma_waitforload * * wait for the DMA engine to load a buffer, and update the state accordingly */ //等待DMA引擎载入一个缓冲 static int s3c2410_dma_waitforload(struct s3c2410_dma_chan *chan, int line) { int timeout = chan->load_timeout;//1 << 18 int took; 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++;//载入加一 while (--timeout > 0) { if ((dma_rdreg(chan, S3C2410_DMA_DSTAT) << (32-20)) != 0) {//左移11位，如果等于0，就表示DMA控制器就绪且传输计数值为0 took = chan->load_timeout - timeout;//已计时间 s3c2410_dma_stats_timeout(chan->stats, took);//在上面 switch (chan->load_state) { case S3C2410_DMALOAD_1LOADED: 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++;//超时，错误加一 } return 0; } /* s3c2410_dma_loadbuffer * * load a buffer, and update the channel state */ //载入 static inline int s3c2410_dma_loadbuffer(struct s3c2410_dma_chan *chan, struct s3c2410_dma_buf *buf) { unsigned long reload; if (buf == NULL) { dmawarn("buffer is NULL\n"); return -EINVAL; } pr_debug("s3c2410_chan_loadbuffer: loading buff %p (0x%08lx,0x%06x)\n", buf, (unsigned long)buf->data, buf->size); /* check the state of the channel before we do anything */ //状态检查，并警告 if (chan->load_state == S3C2410_DMALOAD_1LOADED) {//有一个载入 dmawarn("load_state is S3C2410_DMALOAD_1LOADED\n"); } if (chan->load_state == S3C2410_DMALOAD_1LOADED_1RUNNING) {//一个载入一个运行 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); //next为空说明是最后一个，就不需要再次载入 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) {//内存物理地址从0x30000000开始 dmawarn("dmaload: buffer is %p\n", (void *)buf->data); } writel(buf->data, chan->addr_reg);//数据写入 dma_wrreg(chan, S3C2410_DMA_DCON, chan->dcon | reload | (buf->size/chan->xfer_unit));//配置 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; } /* s3c2410_dma_call_op * * small routine to call the op routine with the given op if it has been * registered */ static void s3c2410_dma_call_op(struct s3c2410_dma_chan *chan, enum s3c2410_chan_op op) { //通过s3c2410_dma_set_opfn函数赋值 if (chan->op_fn != NULL) { (chan->op_fn)(chan, op); } } /* 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 0 pr_debug("callback_fn=%p, buf=%p, id=%p, size=%d, result=%d\n", chan->callback_fn, buf, buf->id, buf->size, result); #endif if (chan->callback_fn != NULL) { (chan->callback_fn)(chan, buf->id, buf->size, result); } } /* 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) { pr_debug("s3c2410_start_dma: already running (%d)\n", chan->state); local_irq_restore(flags); return 0; } //记录状态 chan->state = S3C2410_DMA_RUNNING; /* check wether there is anything to load, and if not, see * if we can find anything to load */ //判断是否已载入载入 if (chan->load_state == S3C2410_DMALOAD_NONE) { if (chan->next == NULL) { printk(KERN_ERR "dma%d: channel has nothing loaded\n", chan->number); chan->state = S3C2410_DMA_IDLE;//没有可载入的state记为空闲 local_irq_restore(flags); return -EINVAL; } s3c2410_dma_loadbuffer(chan, chan->next);//载入缓存 } dbg_showchan(chan);//调试信息 /* enable the channel */ if (!chan->irq_enabled) { enable_irq(chan->irq);//如果中断关闭，开启中断 chan->irq_enabled = 1; } /* start the channel going */ tmp = dma_rdreg(chan, S3C2410_DMA_DMASKTRIG); tmp &= ~S3C2410_DMASKTRIG_STOP; tmp |= S3C2410_DMASKTRIG_ON; dma_wrreg(chan, S3C2410_DMA_DMASKTRIG, tmp);//开始运行 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);//回调 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 */ if (chan->next != NULL) { if (chan->load_state == S3C2410_DMALOAD_1LOADED) {//已有一个正在载入 if (s3c2410_dma_waitforload(chan, __LINE__) == 0) {//等待... pr_debug("%s: buff not yet loaded, no more todo\n", __func__); } else { //这里还有下面的，可以看出在s3c2410_dma_loadbuffer中 //S3C2410_DMALOAD_1RUNNING会使用AUTORELOAD模式 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; } /* 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) { if (chan->load_state == S3C2410_DMALOAD_NONE || chan->load_state == S3C2410_DMALOAD_1RUNNING) return 1; return 0; } /* 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. */ //把数据加入链表 int s3c2410_dma_enqueue(unsigned int channel, void *id, dma_addr_t data, int size) { struct s3c2410_dma_chan *chan = s3c_dma_lookup_channel(channel); struct s3c2410_dma_buf *buf; unsigned long flags; if (chan == NULL) return -EINVAL; pr_debug("%s: id=%p, data=%08x, size=%d\n", __func__, id, (unsigned int)data, size); buf = kmem_cache_alloc(dma_kmem, GFP_ATOMIC);//申请内存 if (buf == NULL) { pr_debug("%s: out of memory (%ld alloc)\n", __func__, (long)sizeof(*buf)); return -ENOMEM; } //pr_debug("%s: new buffer %p\n", __func__, buf); //dbg_showchan(chan); //给buf赋值 buf->next = NULL; buf->data = buf->ptr = data; buf->size = size; buf->id = id; buf->magic = BUF_MAGIC; local_irq_save(flags); //chan->curr赋值并把buf加入链表中 if (chan->curr == NULL) { /* we've got nothing loaded... */ pr_debug("%s: buffer %p queued onto empty channel\n", __func__, buf); chan->curr = buf; chan->end = buf; chan->next = NULL; } else { pr_debug("dma%d: %s: buffer %p queued onto non-empty channel\n", chan->number, __func__, buf); if (chan->end == NULL) pr_debug("dma%d: %s: %p not empty, and chan->end==NULL?\n", chan->number, __func__, chan); chan->end->next = buf; chan->end = buf; } /* if necessary, update the next buffer field */ if (chan->next == NULL) chan->next = buf; /* check to see if we can load a buffer */ if (chan->state == S3C2410_DMA_RUNNING) { if (chan->load_state == S3C2410_DMALOAD_1LOADED && 1) {//当前是否有一个在传输 if (s3c2410_dma_waitforload(chan, __LINE__) == 0) {//等待 printk(KERN_ERR "dma%d: loadbuffer:" "timeout loading buffer\n", chan->number); dbg_showchan(chan); local_irq_restore(flags); return -EINVAL; } } while (s3c2410_dma_canload(chan) && chan->next != NULL) {//可加载且chan->next不为空 s3c2410_dma_loadbuffer(chan, chan->next); } } else if (chan->state == S3C2410_DMA_IDLE) { if (chan->flags & S3C2410_DMAF_AUTOSTART) {//如果设置为自动运行，就调用start函数 s3c2410_dma_ctrl(chan->number | DMACH_LOW_LEVEL, S3C2410_DMAOP_START); } } local_irq_restore(flags); return 0; } EXPORT_SYMBOL(s3c2410_dma_enqueue); static inline void s3c2410_dma_freebuf(struct s3c2410_dma_buf *buf) { int magicok = (buf->magic == BUF_MAGIC); buf->magic = -1; if (magicok) { kmem_cache_free(dma_kmem, buf); } else { printk("s3c2410_dma_freebuf: buff %p with bad magic\n", buf); } } /* 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) { /* flag error? */ printk(KERN_ERR "dma%d: timeout waiting for load (%s)\n", chan->number, __func__); return; } break; case S3C2410_DMALOAD_1LOADED_1RUNNING: /* I believe 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... */ dma_wrreg(chan, S3C2410_DMA_DCON, chan->dcon | S3C2410_DCON_NORELOAD); } #define dmadbg2(x...) 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; dbg_showchan(chan); /* modify the channel state */ //更新状态 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 */ //更新链表 chan->curr = buf->next; buf->next = NULL; if (buf->magic != BUF_MAGIC) { printk(KERN_ERR "dma%d: %s: buf %p incorrect magic\n", chan->number, __func__, buf); return IRQ_HANDLED; } s3c2410_dma_buffdone(chan, buf, S3C2410_RES_OK);//回调，使一些事情工作正常 /* free resouces */ s3c2410_dma_freebuf(buf);//释放空间 } 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 */ 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) {//等待传输完 /* flag error? */ printk(KERN_ERR "dma%d: timeout waiting for load (%s)\n", chan->number, __func__); 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);//再次载入 local_irq_restore(flags); } else { s3c2410_dma_lastxfer(chan);//最后一个缓冲区 /* 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 } } no_load: return IRQ_HANDLED; } static struct s3c2410_dma_chan *s3c2410_dma_map_channel(int channel); /* s3c2410_request_dma * * get control of an dma channel */ //获取一个dma通道 //下面你会看到，获取一个通道信息并注册中断 int s3c2410_dma_request(enum dma_ch 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); //请求一个通道，下面有详细说明 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;//标志为使用 if (!chan->irq_claimed) { pr_debug("dma%d: %s : requesting irq %d\n", channel, __func__, chan->irq); chan->irq_claimed = 1;//中断声明标志为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; } EXPORT_SYMBOL(s3c2410_dma_request); /* 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. */ int s3c2410_dma_free(enum dma_ch channel, struct s3c2410_dma_client *client) { struct s3c2410_dma_chan *chan = s3c_dma_lookup_channel(channel); unsigned long flags; if (chan == NULL) return -EINVAL; local_irq_save(flags); if (chan->client != client) {//检查是否为正确通道 printk(KERN_WARNING "dma%d: possible free from different client (channel %p, passed %p)\n", channel, chan->client, client); } /* sort out stopping and freeing the channel */ if (chan->state != S3C2410_DMA_IDLE) { pr_debug("%s: need to stop dma channel %p\n", __func__, chan); /* possibly flush the channel */ s3c2410_dma_ctrl(channel, S3C2410_DMAOP_STOP);//不是空闲，就停止通道 } chan->client = NULL; chan->in_use = 0; if (chan->irq_claimed) free_irq(chan->irq, (void *)chan);//如果注册的中断就释放 chan->irq_claimed = 0; if (!(channel & DMACH_LOW_LEVEL)) s3c_dma_chan_map[channel] = NULL;//对应的数据置空 local_irq_restore(flags); return 0; } EXPORT_SYMBOL(s3c2410_dma_free); static int s3c2410_dma_dostop(struct s3c2410_dma_chan *chan) { unsigned long flags; unsigned long tmp; pr_debug("%s:\n", __func__); dbg_showchan(chan);//调试不看了 local_irq_save(flags); s3c2410_dma_call_op(chan, S3C2410_DMAOP_STOP); //(chan->op_fn)(chan, op); 回调函数 tmp = dma_rdreg(chan, S3C2410_DMA_DMASKTRIG);//读对应通道的寄存器 tmp |= S3C2410_DMASKTRIG_STOP;//DMASKTRIG的第2位是STOP //tmp &= ~S3C2410_DMASKTRIG_ON; dma_wrreg(chan, S3C2410_DMA_DMASKTRIG, tmp); #if 0 //为了适合WinCE，关闭再加载 /* 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 /* should stop do this, or should we wait for flush? */ chan->state = S3C2410_DMA_IDLE;//dma状态 chan->load_state = S3C2410_DMALOAD_NONE;//dma数据传输状态 local_irq_restore(flags); return 0; } static void s3c2410_dma_waitforstop(struct s3c2410_dma_chan *chan) { unsigned long tmp; unsigned int timeout = 0x10000; while (timeout-- > 0) { tmp = dma_rdreg(chan, S3C2410_DMA_DMASKTRIG); if (!(tmp & S3C2410_DMASKTRIG_ON))//判断DMASKTRIG寄存器第1位是否为0 return; } pr_debug("dma%d: failed to stop?\n", chan->number); } /* s3c2410_dma_flush * * stop the channel, and remove all current and pending transfers */ //停止通道，并移除当前和即将发生的传输 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", __func__, chan, chan->number); dbg_showchan(chan); local_irq_save(flags); if (chan->state != S3C2410_DMA_IDLE) { pr_debug("%s: stopping channel...\n", __func__ ); //不是空闲，调用s3c2410_dma_dostop s3c2410_dma_ctrl(chan->number, S3C2410_DMAOP_STOP); } buf = chan->curr; if (buf == NULL) buf = chan->next; //清除数据 chan->curr = chan->next = chan->end = NULL; //释放空间 if (buf != NULL) { for ( ; buf != NULL; buf = next) { next = buf->next; pr_debug("%s: free buffer %p, next %p\n", __func__, buf, buf->next); s3c2410_dma_buffdone(chan, buf, S3C2410_RES_ABORT);//回调函数调用 s3c2410_dma_freebuf(buf);//就是调用kmem_cache_free释放 } } dbg_showregs(chan); s3c2410_dma_waitforstop(chan);//等待停止 #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; } 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 */ //下面的判断可以查看s3c2410_dma_start() 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", __func__); } 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; } //dma 控制函数 int s3c2410_dma_ctrl(enum dma_ch channel, enum s3c2410_chan_op op) { struct s3c2410_dma_chan *chan = s3c_dma_lookup_channel(channel); if (chan == NULL) return -EINVAL; switch (op) { case S3C2410_DMAOP_START://开始 return s3c2410_dma_start(chan); case S3C2410_DMAOP_STOP://停止 return s3c2410_dma_dostop(chan); case S3C2410_DMAOP_PAUSE://暂停 case S3C2410_DMAOP_RESUME: return -ENOENT; case S3C2410_DMAOP_FLUSH://冲掉 return s3c2410_dma_flush(chan); case S3C2410_DMAOP_STARTED://再次开始 return s3c2410_dma_started(chan); case S3C2410_DMAOP_TIMEOUT://超时 return 0; } return -ENOENT; /* unknown, don't bother */ } EXPORT_SYMBOL(s3c2410_dma_ctrl); /* DMA configuration for each channel * * DISRCC -> source of the DMA (AHB,APB) * 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) */ int s3c2410_dma_config(enum dma_ch channel, int xferunit) { struct s3c2410_dma_chan *chan = s3c_dma_lookup_channel(channel); unsigned int dcon; pr_debug("%s: chan=%d, xfer_unit=%d\n", __func__, channel, xferunit); if (chan == NULL) return -EINVAL; dcon = chan->dcon & dma_sel.dcon_mask; pr_debug("%s: dcon is %08x\n", __func__, dcon); //DCON寄存器的24~26位选择请求源 switch (chan->req_ch) { case DMACH_I2S_IN: case DMACH_I2S_OUT: case DMACH_PCM_IN: case DMACH_PCM_OUT: case DMACH_MIC_IN: default: dcon |= S3C2410_DCON_HANDSHAKE; dcon |= S3C2410_DCON_SYNC_PCLK; break; case DMACH_SDI: /* note, ensure if need HANDSHAKE or not */ dcon |= S3C2410_DCON_SYNC_PCLK; break; case DMACH_XD0: case DMACH_XD1: dcon |= S3C2410_DCON_HANDSHAKE; dcon |= S3C2410_DCON_SYNC_HCLK; break; } //上面的HANDSHAKE是选择握手模式 //除了SDI要选，其他的都是握手模式，chan->dcon来记录你的dcon的配置 //传输大小 switch (xferunit) { case 1: dcon |= S3C2410_DCON_BYTE; break; case 2: dcon |= S3C2410_DCON_HALFWORD; break; case 4: dcon |= S3C2410_DCON_WORD; break; default: pr_debug("%s: bad transfer size %d\n", __func__, xferunit); return -EINVAL; } dcon |= S3C2410_DCON_HWTRIG;//硬件触发 dcon |= S3C2410_DCON_INTREQ;//所有传输完成产生中断 pr_debug("%s: dcon now %08x\n", __func__, dcon); //记录下配置 chan->dcon = dcon; chan->xfer_unit = xferunit; return 0; } EXPORT_SYMBOL(s3c2410_dma_config); /* s3c2410_dma_devconfig * * configure the dma source/destination hardware type and address * * source: DMA_FROM_DEVICE: source is hardware * DMA_TO_DEVICE: source is memory * * devaddr: physical address of the source */ int s3c2410_dma_devconfig(enum dma_ch channel, enum dma_data_direction source, unsigned long devaddr) { struct s3c2410_dma_chan *chan = s3c_dma_lookup_channel(channel); unsigned int hwcfg; if (chan == NULL) return -EINVAL; pr_debug("%s: source=%d, devaddr=%08lx\n", __func__, (int)source, devaddr); chan->source = source;//源类型，内存或者硬件 chan->dev_addr = devaddr;// switch (chan->req_ch) { case DMACH_XD0: case DMACH_XD1: hwcfg = 0; /* AHB */ break; default: hwcfg = S3C2410_DISRCC_APB; } //除了XD0和XD1在AHB总线上，其他都是APB /* always assume our peripheral desintation is a fixed * address in memory. */ //总是认为我们的外围设备是一个固定的地址 hwcfg |= S3C2410_DISRCC_INC;//在传输后地址不改变 switch (source) { case DMA_FROM_DEVICE://源是硬件 /* source is hardware */ pr_debug("%s: hw source, devaddr=%08lx, hwcfg=%d\n", __func__, devaddr, hwcfg); dma_wrreg(chan, S3C2410_DMA_DISRCC, hwcfg & 3);//源控制 dma_wrreg(chan, S3C2410_DMA_DISRC, devaddr);//源地址 dma_wrreg(chan, S3C2410_DMA_DIDSTC, (0<<1) | (0<<0));//目标控制：系统总线，地址增加 chan->addr_reg = dma_regaddr(chan, S3C2410_DMA_DIDST);//记下内存地址 break; case DMA_TO_DEVICE://源是内存 /* source is memory */ pr_debug("%s: mem source, devaddr=%08lx, hwcfg=%d\n", __func__, devaddr, hwcfg); dma_wrreg(chan, S3C2410_DMA_DISRCC, (0<<1) | (0<<0));//源：系统总线，地址增加 dma_wrreg(chan, S3C2410_DMA_DIDST, devaddr);//目标地址地址 dma_wrreg(chan, S3C2410_DMA_DIDSTC, hwcfg & 3);//目标控制 chan->addr_reg = dma_regaddr(chan, S3C2410_DMA_DISRC);//记下内存地址 break; default: printk(KERN_ERR "dma%d: invalid source type (%d)\n", channel, source); return -EINVAL; } if (dma_sel.direction != NULL)//s3c2440为空 (dma_sel.direction)(chan, chan->map, source); return 0; } EXPORT_SYMBOL(s3c2410_dma_devconfig); /* s3c2410_dma_getposition * * returns the current transfer points for the dma source and destination */ //当前源或目标地址 int s3c2410_dma_getposition(enum dma_ch channel, dma_addr_t *src, dma_addr_t *dst) { struct s3c2410_dma_chan *chan = s3c_dma_lookup_channel(channel); if (chan == NULL) return -EINVAL; if (src != NULL) *src = dma_rdreg(chan, S3C2410_DMA_DCSRC); if (dst != NULL) *dst = dma_rdreg(chan, S3C2410_DMA_DCDST); return 0; } EXPORT_SYMBOL(s3c2410_dma_getposition); /* system core operations */ #ifdef CONFIG_PM static void s3c2410_dma_suspend_chan(struct s3c2410_dma_chan *cp) { printk(KERN_DEBUG "suspending dma channel %d\n", cp->number); if (dma_rdreg(cp, S3C2410_DMA_DMASKTRIG) & S3C2410_DMASKTRIG_ON) { /* the dma channel is still working, which is probably * a bad thing to do over suspend/resume. We stop the * channel and assume that the client is either going to * retry after resume, or that it is broken. */ printk(KERN_INFO "dma: stopping channel %d due to suspend\n", cp->number); s3c2410_dma_dostop(cp); } } static int s3c2410_dma_suspend(void) { struct s3c2410_dma_chan *cp = s3c2410_chans; int channel; for (channel = 0; channel < dma_channels; cp++, channel++) s3c2410_dma_suspend_chan(cp); return 0; } static void s3c2410_dma_resume_chan(struct s3c2410_dma_chan *cp) { unsigned int no = cp->number | DMACH_LOW_LEVEL; /* restore channel's hardware configuration */ if (!cp->in_use) return; printk(KERN_INFO "dma%d: restoring configuration\n", cp->number); s3c2410_dma_config(no, cp->xfer_unit); s3c2410_dma_devconfig(no, cp->source, cp->dev_addr); /* re-select the dma source for this channel */ if (cp->map != NULL) dma_sel.select(cp, cp->map); } static void s3c2410_dma_resume(void) { struct s3c2410_dma_chan *cp = s3c2410_chans + dma_channels - 1; int channel; for (channel = dma_channels - 1; channel >= 0; cp++, channel--) s3c2410_dma_resume_chan(cp); } #else #define s3c2410_dma_suspend NULL #define s3c2410_dma_resume NULL #endif /* CONFIG_PM */ /* struct syscore_ops { struct list_head node; int (*suspend)(void); void (*resume)(void); void (*shutdown)(void); }; 这个syscore是通过一个全局的list管理的,如下 LIST_HEAD(syscore_ops_list); */ struct syscore_ops dma_syscore_ops = { .suspend = s3c2410_dma_suspend, .resume = s3c2410_dma_resume, }; /* kmem cache implementation */ //下面看到 static void s3c2410_dma_cache_ctor(void *p) { memset(p, 0, sizeof(struct s3c2410_dma_buf)); } /* initialisation code */ static int __init s3c24xx_dma_syscore_init(void) { //注册的实质就是 //list_add_tail(&ops->node, &syscore_ops_list); //加入链表 register_syscore_ops(&dma_syscore_ops); return 0; } //late_initcall启动时会执行，在那个阶段我们就不管了 late_initcall(s3c24xx_dma_syscore_init); /* 下面这个函数告诉我们这些__init函数的调用位置 static int __init s3c2440_dma_add(struct sys_device *sysdev) { s3c2410_dma_init(); s3c24xx_dma_order_set(&s3c2440_dma_order); return s3c24xx_dma_init_map(&s3c2440_dma_sel); } static struct sysdev_driver s3c2440_dma_driver = { .add = s3c2440_dma_add, }; static int __init s3c2440_dma_init(void) { return sysdev_driver_register(&s3c2440_sysclass, &s3c2440_dma_driver); } struct sysdev_class s3c2440_sysclass = { .name = "s3c2440-core", }; static struct sys_device s3c2440_sysdev = { .cls = &s3c2440_sysclass, }; 在s3c2440_init()中会调用 sysdev_register(&s3c2440_sysdev); 我们从这可以看到设备与驱动的概念，当然这不是我们的重点，我只说想说 s3c2440_dma_add初始化会被调用，我们就安初始化调用过程来看代码 启动时调用 arch_initcall(s3c2440_dma_init); */ //s3c24xx_dma_init在下面s3c2410_dma_init()被调用 //s3c2440或s3c2410平台s3c24xx_dma_init(4, IRQ_DMA0, 0x40); //4个通道，中断号为IRQ_DMA0，0x40 * 4就是io要映射的大小 int __init s3c24xx_dma_init(unsigned int channels, unsigned int irq, unsigned int stride) { struct s3c2410_dma_chan *cp; int channel; int ret; printk("S3C24XX DMA Driver, Copyright 2003-2006 Simtec Electronics\n"); dma_channels = channels; //寄存器映射 dma_base = ioremap(S3C24XX_PA_DMA, stride * channels); if (dma_base == NULL) { printk(KERN_ERR "dma failed to remap register block\n"); return -ENOMEM; } //申请后备缓存 dma_kmem = kmem_cache_create("dma_desc", sizeof(struct s3c2410_dma_buf), 0, SLAB_HWCACHE_ALIGN, s3c2410_dma_cache_ctor); /* 原型： struct kmem_cache *kmem_cache_create(const char *name, size_t size, size_t align, unsigned long flags, void (*ctor)(void *)) SLAB_HWCACHE_ALIGN: 这个标志需要每个数据对象被对齐到一个缓存行; 实际对齐依赖主机平 台的缓存分布. 这个选项可以是一个好的选择, 如果在 SMP 机器上你的 缓存包含频繁存取的项. 但是, 用来获得缓存行对齐的填充可以浪费可 观的内存量. s3c2410_dma_cache_ctor： 构造函数，上面可以看到就是把申请的内存空间清零。 */ if (dma_kmem == NULL) { printk(KERN_ERR "dma failed to make kmem cache\n"); ret = -ENOMEM; goto err; } /* 在mach-s3c2410/include/mach/dma.h下定义的结构体 struct s3c2410_dma_chan s3c2410_chans[S3C_DMA_CHANNELS]; */ for (channel = 0; channel < channels; channel++) { cp = &s3c2410_chans[channel]; memset(cp, 0, sizeof(struct s3c2410_dma_chan)); /* dma channel irqs are in order.. */ cp->number = channel; //通道号 cp->irq = channel + irq; //中断号 cp->regs = dma_base + (channel * stride); //寄存器基地址 /* point current stats somewhere */ /* struct s3c2410_dma_stats *stats; struct s3c2410_dma_stats stats_store; 下面就是个指针初始化 */ cp->stats = &cp->stats_store; cp->stats_store.timeout_shortest = LONG_MAX;//#define LONG_MAX ((long)(~0UL>>1)) /* basic channel configuration */ cp->load_timeout = 1<<18;//向dma载入缓冲的超时时间 printk("DMA channel %d at %p, irq %d\n", cp->number, cp->regs, cp->irq); } return 0; err: kmem_cache_destroy(dma_kmem); iounmap(dma_base); dma_base = NULL; return ret; } int __init s3c2410_dma_init(void) { return s3c24xx_dma_init(4, IRQ_DMA0, 0x40); } static inline int is_channel_valid(unsigned int channel) { //#define DMA_CH_VALID (1<<31) return (channel & DMA_CH_VALID); } static struct s3c24xx_dma_order *dma_order; /* s3c2410_dma_map_channel() * * turn the virtual channel number into a real, and un-used hardware * channel. * * first, try the dma ordering given to us by either the relevant * dma code, or the board. Then just find the first usable free * channel */ //根据虚拟通道号，找到一个可以的通道 //实际就是根据channel从数组s3c2440_dma_order和 //s3c2440_dma_mapping和中找到对应且可用的元素 //s3c2410_dma_request()会调用这个函数 static struct s3c2410_dma_chan *s3c2410_dma_map_channel(int channel) { struct s3c24xx_dma_order_ch *ord = NULL; struct s3c24xx_dma_map *ch_map; struct s3c2410_dma_chan *dmach; int ch; //dma_sel.map就是s3c2440_dma_mappings[] //dma_sel.map_size就是ARRAY_SIZE(s3c2440_dma_mappings) if (dma_sel.map == NULL || channel > dma_sel.map_size) return NULL; ch_map = dma_sel.map + channel; //从上面这句可以看出这个channel不是指dma的4个通道 //而是s3c2440_dma_mappings[]对应的数组元素,下面有 /*channel的值如下 enum dma_ch { DMACH_XD0, DMACH_XD1, DMACH_SDI, DMACH_SPI0, DMACH_SPI1, DMACH_UART0, DMACH_UART1, ... 和s3c2440_dma_mappings[]对应 */ /* first, try the board mapping */ if (dma_order) { ord = &dma_order->channels[channel];//找到对应的 for (ch = 0; ch < dma_channels; ch++) { int tmp; if (!is_channel_valid(ord->list[ch]))//判断通道可用 continue; tmp = ord->list[ch] & ~DMA_CH_VALID;//标志为不可用 //s3c2410_dma_request函数会使in_use变为1 if (s3c2410_chans[tmp].in_use == 0) { ch = tmp; goto found; } } if (ord->flags & DMA_CH_NEVER) return NULL; } /* second, search the channel map for first free */ for (ch = 0; ch < dma_channels; ch++) { if (!is_channel_valid(ch_map->channels[ch]))//判断可用 continue; if (s3c2410_chans[ch].in_use == 0) { printk("mapped channel %d to %d\n", channel, ch); break; } } /* 上面的is_channel_valid是在平台提供的数组中的标记 in_use是此代码中的标记。 */ if (ch >= dma_channels) return NULL; /* update our channel mapping */ found: dmach = &s3c2410_chans[ch]; dmach->map = ch_map; //对应的struct s3c24xx_dma_map结构体 dmach->req_ch = channel; s3c_dma_chan_map[channel] = dmach;//放入struct s3c2410_dma_chan结构体中 /* select the channel */ (dma_sel.select)(dmach, ch_map);//下面有s3c2440的select函数s3c2440_dma_select() return dmach; } static int s3c24xx_dma_check_entry(struct s3c24xx_dma_map *map, int ch) { return 0; } int __init s3c24xx_dma_init_map(struct s3c24xx_dma_selection *sel) { //传入的是s3c2440_dma_sel /* struct s3c24xx_dma_map { const char *name; unsigned long channels[S3C_DMA_CHANNELS]; unsigned long channels_rx[S3C_DMA_CHANNELS]; }; 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); void (*direction)(struct s3c2410_dma_chan *chan, struct s3c24xx_dma_map *map, enum dma_data_direction dir); }; static struct s3c24xx_dma_map __initdata s3c2440_dma_mappings[] = { [DMACH_XD0] = { .name = "xdreq0", .channels[0] = S3C2410_DCON_CH0_XDREQ0 | DMA_CH_VALID, }, [DMACH_XD1] = { .name = "xdreq1", .channels[1] = S3C2410_DCON_CH1_XDREQ1 | DMA_CH_VALID, }, [DMACH_SDI] = { .name = "sdi", .channels[0] = S3C2410_DCON_CH0_SDI | DMA_CH_VALID, .channels[1] = S3C2440_DCON_CH1_SDI | DMA_CH_VALID, .channels[2] = S3C2410_DCON_CH2_SDI | DMA_CH_VALID, .channels[3] = S3C2410_DCON_CH3_SDI | DMA_CH_VALID, }, //太长没贴完，就是支持的外设信息 static void s3c2440_dma_select(struct s3c2410_dma_chan *chan, struct s3c24xx_dma_map *map) { chan->dcon = map->channels[chan->number] & ~DMA_CH_VALID;//选择一个通道并置为不可用 } static struct s3c24xx_dma_selection __initdata s3c2440_dma_sel = { .select = s3c2440_dma_select, .dcon_mask = 7 << 24, //dcon寄存器的24~26位 源选择 .map = s3c2440_dma_mappings, .map_size = ARRAY_SIZE(s3c2440_dma_mappings), }; */ struct s3c24xx_dma_map *nmap; size_t map_sz = sizeof(*nmap) * sel->map_size; int ptr; 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; //上面一段就是,申请内存，把s3c2440_dma_sel的信息放入dma_sel中 for (ptr = 0; ptr < sel->map_size; ptr++) s3c24xx_dma_check_entry(nmap+ptr, ptr);//在上面，空函数 return 0; } int __init s3c24xx_dma_order_set(struct s3c24xx_dma_order *ord) { //传入的就是s3c2440_dma_order /* struct s3c24xx_dma_order_ch { unsigned int list[S3C_DMA_CHANNELS]; // list of channels unsigned int flags; // flags }; struct s3c24xx_dma_order { struct s3c24xx_dma_order_ch channels[DMACH_MAX]; }; DMACH_MAX指的是外设的最大ID,通过类似DMACH_UART0_TX来表示外设 S3C_DMA_CHANNELS是最大通道数，s3c2440是4个通道 static struct s3c24xx_dma_order __initdata s3c2440_dma_order = { .channels = { [DMACH_SDI] = { .list = { [0] = 3 | DMA_CH_VALID, [1] = 2 | DMA_CH_VALID, [2] = 1 | DMA_CH_VALID, [3] = 0 | DMA_CH_VALID, }, }, [DMACH_I2S_IN] = { .list = { [0] = 1 | DMA_CH_VALID, [1] = 2 | DMA_CH_VALID, }, }, [DMACH_I2S_OUT] = { .list = { [0] = 2 | DMA_CH_VALID, [1] = 1 | DMA_CH_VALID, }, }, [DMACH_PCM_IN] = { .list = { [0] = 2 | DMA_CH_VALID, [1] = 1 | DMA_CH_VALID, ... 太多，没贴完。 */ struct s3c24xx_dma_order *nord = dma_order; if (nord == NULL)//为空的话重分配 nord = kmalloc(sizeof(struct s3c24xx_dma_order), GFP_KERNEL); if (nord == NULL) { printk(KERN_ERR "no memory to store dma channel order\n"); return -ENOMEM; } dma_order = nord; memcpy(nord, ord, sizeof(struct s3c24xx_dma_order)); return 0; }
如果你看懂了上面的代码，下面的plat-samsung中的代码基本不用分析了
/* linux/arch/arm/plat-samsung/s3c-dma-ops.c
*
* Copyright (c) 2011 Samsung Electronics Co., Ltd.
* http://www.samsung.com
*
* Samsung S3C-DMA Operations
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/export.h>
#include <mach/dma.h>
struct cb_data {
void (*fp) (void *);
void *fp_param;
unsigned ch;
struct list_head node;
};
static LIST_HEAD(dma_list);
//s3c2410_dma_buffdone(chan, buf, S3C2410_RES_ABORT);
//s3c2410_dma_buffdone(chan, buf, S3C2410_RES_OK);
/*
if (chan->callback_fn != NULL) {
(chan->callback_fn)(chan, buf->id, buf->size, result);
}
*/
static void s3c_dma_cb(struct s3c2410_dma_chan *channel, void *param,
int size, enum s3c2410_dma_buffresult res)
{
struct cb_data *data = param;
data->fp(data->fp_param);
}
static unsigned s3c_dma_request(enum dma_ch dma_ch,
struct samsung_dma_info *info)
{
struct cb_data *data;
if (s3c2410_dma_request(dma_ch, info->client, NULL) < 0) {
s3c2410_dma_free(dma_ch, info->client);
return 0;
}
data = kzalloc(sizeof(struct cb_data), GFP_KERNEL);
data->ch = dma_ch;
list_add_tail(&data->node, &dma_list);
s3c2410_dma_devconfig(dma_ch, info->direction, info->fifo);
if (info->cap == DMA_CYCLIC)
s3c2410_dma_setflags(dma_ch, S3C2410_DMAF_CIRCULAR);
s3c2410_dma_config(dma_ch, info->width);
return (unsigned)dma_ch;
}
static int s3c_dma_release(unsigned ch, struct s3c2410_dma_client *client)
{
struct cb_data *data;
list_for_each_entry(data, &dma_list, node)
if (data->ch == ch)
break;
list_del(&data->node);
s3c2410_dma_free(ch, client);
kfree(data);
return 0;
}
static int s3c_dma_prepare(unsigned ch, struct samsung_dma_prep_info *info)
{
struct cb_data *data;
int len = (info->cap == DMA_CYCLIC) ? info->period : info->len;
list_for_each_entry(data, &dma_list, node)
if (data->ch == ch)
break;
if (!data->fp) {
s3c2410_dma_set_buffdone_fn(ch, s3c_dma_cb);
data->fp = info->fp;
data->fp_param = info->fp_param;
}
s3c2410_dma_enqueue(ch, (void *)data, info->buf, len);
return 0;
}
static inline int s3c_dma_trigger(unsigned ch)
{
return s3c2410_dma_ctrl(ch, S3C2410_DMAOP_START);
}
static inline int s3c_dma_started(unsigned ch)
{
return s3c2410_dma_ctrl(ch, S3C2410_DMAOP_STARTED);
}
static inline int s3c_dma_flush(unsigned ch)
{
return s3c2410_dma_ctrl(ch, S3C2410_DMAOP_FLUSH);
}
static inline int s3c_dma_stop(unsigned ch)
{
return s3c2410_dma_ctrl(ch, S3C2410_DMAOP_STOP);
}
static struct samsung_dma_ops s3c_dma_ops = {
.request = s3c_dma_request,
.release = s3c_dma_release,
.prepare = s3c_dma_prepare,
.trigger = s3c_dma_trigger,
.started = s3c_dma_started,
.flush = s3c_dma_flush,
.stop = s3c_dma_stop,
};
void *s3c_dma_get_ops(void)
{
return &s3c_dma_ops;
}
EXPORT_SYMBOL(s3c_dma_get_ops);