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
/* 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);