C++ dmaengine_slave_config函数代码示例

static void mtk8250_dma_enable(struct uart_8250_port *up)
{
	struct uart_8250_dma *dma = up->dma;
	struct mtk8250_data *data = up->port.private_data;
	int lcr = serial_in(up, UART_LCR);

	if (data->rx_status != DMA_RX_START)
		return;

	dma->rxconf.direction		= DMA_DEV_TO_MEM;
	dma->rxconf.src_addr_width	= dma->rx_size / 1024;
	dma->rxconf.src_addr		= dma->rx_addr;

	dma->txconf.direction		= DMA_MEM_TO_DEV;
	dma->txconf.dst_addr_width	= MTK_UART_TX_SIZE / 1024;
	dma->txconf.dst_addr		= dma->tx_addr;

	serial_out(up, UART_FCR, UART_FCR_ENABLE_FIFO | UART_FCR_CLEAR_RCVR |
		UART_FCR_CLEAR_XMIT);
	serial_out(up, MTK_UART_DMA_EN,
		   MTK_UART_DMA_EN_RX | MTK_UART_DMA_EN_TX);

	serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
	serial_out(up, UART_EFR, UART_EFR_ECB);
	serial_out(up, UART_LCR, lcr);

	if (dmaengine_slave_config(dma->rxchan, &dma->rxconf) != 0)
		pr_err("failed to configure rx dma channel\n");
	if (dmaengine_slave_config(dma->txchan, &dma->txconf) != 0)
		pr_err("failed to configure tx dma channel\n");

	data->rx_status = DMA_RX_RUNNING;
	data->rx_pos = 0;
	mtk8250_rx_dma(up);
}

static unsigned samsung_dmadev_request(enum dma_ch dma_ch,
				struct samsung_dma_info *info)
{
	struct dma_chan *chan;
	dma_cap_mask_t mask;
	struct dma_slave_config slave_config;

	dma_cap_zero(mask);
	dma_cap_set(info->cap, mask);

	chan = dma_request_channel(mask, pl330_filter, (void *)dma_ch);

	if (info->direction == DMA_FROM_DEVICE) {
		memset(&slave_config, 0, sizeof(struct dma_slave_config));
		slave_config.direction = info->direction;
		slave_config.src_addr = info->fifo;
		slave_config.src_addr_width = info->width;
		slave_config.src_maxburst = 1;
		dmaengine_slave_config(chan, &slave_config);
	} else if (info->direction == DMA_TO_DEVICE) {
		memset(&slave_config, 0, sizeof(struct dma_slave_config));
		slave_config.direction = info->direction;
		slave_config.dst_addr = info->fifo;
		slave_config.dst_addr_width = info->width;
		slave_config.dst_maxburst = 1;
		dmaengine_slave_config(chan, &slave_config);
	}

	return (unsigned)chan;
}

static void bcm2835_dma_init(struct spi_master *master, struct device *dev)
{
	struct dma_slave_config slave_config;
	const __be32 *addr;
	dma_addr_t dma_reg_base;
	int ret;

	/* base address in dma-space */
	addr = of_get_address(master->dev.of_node, 0, NULL, NULL);
	if (!addr) {
		dev_err(dev, "could not get DMA-register address - not using dma mode\n");
		goto err;
	}
	dma_reg_base = be32_to_cpup(addr);

	/* get tx/rx dma */
	master->dma_tx = dma_request_slave_channel(dev, "tx");
	if (!master->dma_tx) {
		dev_err(dev, "no tx-dma configuration found - not using dma mode\n");
		goto err;
	}
	master->dma_rx = dma_request_slave_channel(dev, "rx");
	if (!master->dma_rx) {
		dev_err(dev, "no rx-dma configuration found - not using dma mode\n");
		goto err_release;
	}

	/* configure DMAs */
	slave_config.direction = DMA_MEM_TO_DEV;
	slave_config.dst_addr = (u32)(dma_reg_base + BCM2835_SPI_FIFO);
	slave_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;

	ret = dmaengine_slave_config(master->dma_tx, &slave_config);
	if (ret)
		goto err_config;

	slave_config.direction = DMA_DEV_TO_MEM;
	slave_config.src_addr = (u32)(dma_reg_base + BCM2835_SPI_FIFO);
	slave_config.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;

	ret = dmaengine_slave_config(master->dma_rx, &slave_config);
	if (ret)
		goto err_config;

	/* all went well, so set can_dma */
	master->can_dma = bcm2835_spi_can_dma;
	master->max_dma_len = 65535; /* limitation by BCM2835_SPI_DLEN */
	/* need to do TX AND RX DMA, so we need dummy buffers */
	master->flags = SPI_MASTER_MUST_RX | SPI_MASTER_MUST_TX;

	return;

err_config:
	dev_err(dev, "issue configuring dma: %d - not using DMA mode\n",
		ret);
err_release:
	bcm2835_dma_release(master);
err:
	return;
}

static int pic32_spi_dma_config(struct pic32_spi *pic32s, u32 dma_width)
{
	int buf_offset = offsetof(struct pic32_spi_regs, buf);
	struct spi_master *master = pic32s->master;
	struct dma_slave_config cfg;
	int ret;

	cfg.device_fc = true;
	cfg.src_addr = pic32s->dma_base + buf_offset;
	cfg.dst_addr = pic32s->dma_base + buf_offset;
	cfg.src_maxburst = pic32s->fifo_n_elm / 2; /* fill one-half */
	cfg.dst_maxburst = pic32s->fifo_n_elm / 2; /* drain one-half */
	cfg.src_addr_width = dma_width;
	cfg.dst_addr_width = dma_width;
	/* tx channel */
	cfg.slave_id = pic32s->tx_irq;
	cfg.direction = DMA_MEM_TO_DEV;
	ret = dmaengine_slave_config(master->dma_tx, &cfg);
	if (ret) {
		dev_err(&master->dev, "tx channel setup failed\n");
		return ret;
	}
	/* rx channel */
	cfg.slave_id = pic32s->rx_irq;
	cfg.direction = DMA_DEV_TO_MEM;
	ret = dmaengine_slave_config(master->dma_rx, &cfg);
	if (ret)
		dev_err(&master->dev, "rx channel setup failed\n");

	return ret;
}

int serial8250_request_dma(struct uart_8250_port *p)
{
	struct uart_8250_dma	*dma = p->dma;
	dma_cap_mask_t		mask;

	/* Default slave configuration parameters */
	dma->rxconf.direction		= DMA_DEV_TO_MEM;
	dma->rxconf.src_addr_width	= DMA_SLAVE_BUSWIDTH_1_BYTE;
	dma->rxconf.src_addr		= p->port.mapbase + UART_RX;

	dma->txconf.direction		= DMA_MEM_TO_DEV;
	dma->txconf.dst_addr_width	= DMA_SLAVE_BUSWIDTH_1_BYTE;
	dma->txconf.dst_addr		= p->port.mapbase + UART_TX;

	dma_cap_zero(mask);
	dma_cap_set(DMA_SLAVE, mask);

	/* Get a channel for RX */
	dma->rxchan = dma_request_slave_channel_compat(mask,
						       dma->fn, dma->rx_param,
						       p->port.dev, "rx");
	if (!dma->rxchan)
		return -ENODEV;

	dmaengine_slave_config(dma->rxchan, &dma->rxconf);

	/* Get a channel for TX */
	dma->txchan = dma_request_slave_channel_compat(mask,
						       dma->fn, dma->tx_param,
						       p->port.dev, "tx");
	if (!dma->txchan) {
		dma_release_channel(dma->rxchan);
		return -ENODEV;
	}

	dmaengine_slave_config(dma->txchan, &dma->txconf);

	/* RX buffer */
	if (!dma->rx_size)
		dma->rx_size = PAGE_SIZE;

	dma->rx_buf = dma_alloc_coherent(dma->rxchan->device->dev, dma->rx_size,
					&dma->rx_addr, GFP_KERNEL);
	if (!dma->rx_buf) {
		dma_release_channel(dma->rxchan);
		dma_release_channel(dma->txchan);
		return -ENOMEM;
	}

	/* TX buffer */
	dma->tx_addr = dma_map_single(dma->txchan->device->dev,
					p->port.state->xmit.buf,
					UART_XMIT_SIZE,
					DMA_TO_DEVICE);

	dev_dbg_ratelimited(p->port.dev, "got both dma channels\n");

	return 0;
}

static int spi_imx_sdma_init(struct device *dev, struct spi_imx_data *spi_imx,
			     struct spi_master *master,
			     const struct resource *res)
{
	int ret;

	/* Prepare for TX DMA: */
	master->dma_tx = dma_request_slave_channel(dev, "tx");
	if (!master->dma_tx) {
		dev_err(dev, "cannot get the TX DMA channel!\n");
		ret = -EINVAL;
		goto err;
	}

	spi_imx->tx_config.direction = DMA_MEM_TO_DEV;
	spi_imx->tx_config.dst_addr = res->start + MXC_CSPITXDATA;
	spi_imx->tx_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
	spi_imx->tx_config.dst_maxburst = spi_imx_get_fifosize(spi_imx) / 4;
	ret = dmaengine_slave_config(master->dma_tx, &spi_imx->tx_config);
	if (ret) {
		dev_err(dev, "error in TX dma configuration.\n");
		goto err;
	}

	/* Prepare for RX : */
	master->dma_rx = dma_request_slave_channel(dev, "rx");
	if (!master->dma_rx) {
		dev_dbg(dev, "cannot get the DMA channel.\n");
		ret = -EINVAL;
		goto err;
	}

	spi_imx->rx_config.direction = DMA_DEV_TO_MEM;
	spi_imx->rx_config.src_addr = res->start + MXC_CSPIRXDATA;
	spi_imx->rx_config.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
	spi_imx->rx_config.src_maxburst = spi_imx_get_fifosize(spi_imx) / 2;
	ret = dmaengine_slave_config(master->dma_rx, &spi_imx->rx_config);
	if (ret) {
		dev_err(dev, "error in RX dma configuration.\n");
		goto err;
	}

	init_completion(&spi_imx->dma_rx_completion);
	init_completion(&spi_imx->dma_tx_completion);
	master->can_dma = spi_imx_can_dma;
	master->max_dma_len = MAX_SDMA_BD_BYTES;
	spi_imx->bitbang.master->flags = SPI_MASTER_MUST_RX |
					 SPI_MASTER_MUST_TX;
	spi_imx->rx_wml = spi_imx->rx_config.src_maxburst;
	spi_imx->tx_wml = spi_imx->tx_config.dst_maxburst;
	spi_imx->dma_is_inited = 1;

	return 0;
err:
	spi_imx_sdma_exit(spi_imx);
	return ret;
}

static int spi_imx_setupxfer(struct spi_device *spi,
				 struct spi_transfer *t)
{
	struct spi_imx_data *spi_imx = spi_master_get_devdata(spi->master);
	struct spi_imx_config config;
	int ret;

	config.bpw = t ? t->bits_per_word : spi->bits_per_word;
	config.speed_hz  = t ? t->speed_hz : spi->max_speed_hz;
	config.mode = spi->mode;
	config.cs = spi->chip_select;

	if (!config.speed_hz)
		config.speed_hz = spi->max_speed_hz;
	if (!config.bpw)
		config.bpw = spi->bits_per_word;

	/* Initialize the functions for transfer */
	if (config.bpw <= 8) {
		spi_imx->rx = spi_imx_buf_rx_u8;
		spi_imx->tx = spi_imx_buf_tx_u8;
		spi_imx->tx_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
		spi_imx->rx_config.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
	} else if (config.bpw <= 16) {
		spi_imx->rx = spi_imx_buf_rx_u16;
		spi_imx->tx = spi_imx_buf_tx_u16;
		spi_imx->tx_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_2_BYTES;
		spi_imx->rx_config.src_addr_width = DMA_SLAVE_BUSWIDTH_2_BYTES;
	} else {
		spi_imx->rx = spi_imx_buf_rx_u32;
		spi_imx->tx = spi_imx_buf_tx_u32;
		spi_imx->tx_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
		spi_imx->rx_config.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
	}

	if (spi_imx->bitbang.master->can_dma &&
	    spi_imx_can_dma(spi_imx->bitbang.master, spi, t)) {
		ret = dmaengine_slave_config(spi_imx->bitbang.master->dma_tx,
						&spi_imx->tx_config);
		if (ret) {
			dev_err(&spi->dev, "error in TX dma configuration.\n");
			return ret;
		}

		ret = dmaengine_slave_config(spi_imx->bitbang.master->dma_rx,
						&spi_imx->rx_config);
		if (ret) {
			dev_err(&spi->dev, "error in RX dma configuration.\n");
			return ret;
		}
	}

	spi_imx->devtype_data->config(spi_imx, &config);

	return 0;
}

static int spi_imx_dma_configure(struct spi_master *master,
				 int bytes_per_word)
{
	int ret;
	enum dma_slave_buswidth buswidth;
	struct dma_slave_config rx = {}, tx = {};
	struct spi_imx_data *spi_imx = spi_master_get_devdata(master);

	if (bytes_per_word == spi_imx->bytes_per_word)
		/* Same as last time */
		return 0;

	switch (bytes_per_word) {
	case 4:
		buswidth = DMA_SLAVE_BUSWIDTH_4_BYTES;
		break;
	case 2:
		buswidth = DMA_SLAVE_BUSWIDTH_2_BYTES;
		break;
	case 1:
		buswidth = DMA_SLAVE_BUSWIDTH_1_BYTE;
		break;
	default:
		return -EINVAL;
	}

	tx.direction = DMA_MEM_TO_DEV;
	tx.dst_addr = spi_imx->base_phys + MXC_CSPITXDATA;
	tx.dst_addr_width = buswidth;
	tx.dst_maxburst = spi_imx->wml;
	ret = dmaengine_slave_config(master->dma_tx, &tx);
	if (ret) {
		dev_err(spi_imx->dev, "TX dma configuration failed with %d\n", ret);
		return ret;
	}

	rx.direction = DMA_DEV_TO_MEM;
	rx.src_addr = spi_imx->base_phys + MXC_CSPIRXDATA;
	rx.src_addr_width = buswidth;
	rx.src_maxburst = spi_imx->wml;
	ret = dmaengine_slave_config(master->dma_rx, &rx);
	if (ret) {
		dev_err(spi_imx->dev, "RX dma configuration failed with %d\n", ret);
		return ret;
	}

	spi_imx->bytes_per_word = bytes_per_word;

	return 0;
}

static int spi_qup_init_dma(struct spi_master *master, resource_size_t base)
{
	struct spi_qup *spi = spi_master_get_devdata(master);
	struct dma_slave_config *rx_conf = &spi->rx_conf,
				*tx_conf = &spi->tx_conf;
	struct device *dev = spi->dev;
	int ret;

	/* allocate dma resources, if available */
	master->dma_rx = dma_request_slave_channel_reason(dev, "rx");
	if (IS_ERR(master->dma_rx))
		return PTR_ERR(master->dma_rx);

	master->dma_tx = dma_request_slave_channel_reason(dev, "tx");
	if (IS_ERR(master->dma_tx)) {
		ret = PTR_ERR(master->dma_tx);
		goto err_tx;
	}

	/* set DMA parameters */
	rx_conf->direction = DMA_DEV_TO_MEM;
	rx_conf->device_fc = 1;
	rx_conf->src_addr = base + QUP_INPUT_FIFO;
	rx_conf->src_maxburst = spi->in_blk_sz;

	tx_conf->direction = DMA_MEM_TO_DEV;
	tx_conf->device_fc = 1;
	tx_conf->dst_addr = base + QUP_OUTPUT_FIFO;
	tx_conf->dst_maxburst = spi->out_blk_sz;

	ret = dmaengine_slave_config(master->dma_rx, rx_conf);
	if (ret) {
		dev_err(dev, "failed to configure RX channel\n");
		goto err;
	}

	ret = dmaengine_slave_config(master->dma_tx, tx_conf);
	if (ret) {
		dev_err(dev, "failed to configure TX channel\n");
		goto err;
	}

	return 0;

err:
	dma_release_channel(master->dma_tx);
err_tx:
	dma_release_channel(master->dma_rx);
	return ret;
}

static int rsnd_dmaen_init(struct rsnd_dai_stream *io,
			   struct rsnd_dma *dma, int id,
			   struct rsnd_mod *mod_from, struct rsnd_mod *mod_to)
{
	struct rsnd_dmaen *dmaen = rsnd_dma_to_dmaen(dma);
	struct rsnd_priv *priv = rsnd_io_to_priv(io);
	struct device *dev = rsnd_priv_to_dev(priv);
	struct dma_slave_config cfg = {};
	int is_play = rsnd_io_is_play(io);
	int ret;

	if (dmaen->chan) {
		dev_err(dev, "it already has dma channel\n");
		return -EIO;
	}

	if (dev->of_node) {
		dmaen->chan = rsnd_dmaen_request_channel(io, mod_from, mod_to);
	} else {
		dma_cap_mask_t mask;

		dma_cap_zero(mask);
		dma_cap_set(DMA_SLAVE, mask);

		dmaen->chan = dma_request_channel(mask, shdma_chan_filter,
						  (void *)id);
	}
	if (IS_ERR_OR_NULL(dmaen->chan)) {
		dmaen->chan = NULL;
		dev_err(dev, "can't get dma channel\n");
		goto rsnd_dma_channel_err;
	}

	cfg.direction	= is_play ? DMA_MEM_TO_DEV : DMA_DEV_TO_MEM;
	cfg.src_addr	= dma->src_addr;
	cfg.dst_addr	= dma->dst_addr;
	cfg.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
	cfg.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;

	dev_dbg(dev, "dma : %pad -> %pad\n",
		&cfg.src_addr, &cfg.dst_addr);

	ret = dmaengine_slave_config(dmaen->chan, &cfg);
	if (ret < 0)
		goto rsnd_dma_init_err;

	return 0;

rsnd_dma_init_err:
	rsnd_dma_quit(io, dma);
rsnd_dma_channel_err:

	/*
	 * DMA failed. try to PIO mode
	 * see
	 *	rsnd_ssi_fallback()
	 *	rsnd_rdai_continuance_probe()
	 */
	return -EAGAIN;
}

/* this may get called several times by oss emulation */
static int omap_pcm_hw_params(struct snd_pcm_substream *substream,
			      struct snd_pcm_hw_params *params)
{
	struct snd_pcm_runtime *runtime = substream->runtime;
	struct snd_soc_pcm_runtime *rtd = substream->private_data;
	struct omap_pcm_dma_data *dma_data;
	struct dma_slave_config config;
	struct dma_chan *chan;
	int err = 0;

	dma_data = snd_soc_dai_get_dma_data(rtd->cpu_dai, substream);

	/* return if this is a bufferless transfer e.g.
	 * codec <--> BT codec or GSM modem -- lg FIXME */
	if (!dma_data)
		return 0;

	snd_pcm_set_runtime_buffer(substream, &substream->dma_buffer);
	runtime->dma_bytes = params_buffer_bytes(params);

	chan = snd_dmaengine_pcm_get_chan(substream);
	if (!chan)
		return -EINVAL;

	/* fills in addr_width and direction */
	err = snd_hwparams_to_dma_slave_config(substream, params, &config);
	if (err)
		return err;

	snd_dmaengine_pcm_set_config_from_dai_data(substream,
			snd_soc_dai_get_dma_data(rtd->cpu_dai, substream),
			&config);

	return dmaengine_slave_config(chan, &config);
}

static int bcm2835_smi_dma_setup(struct bcm2835_smi_instance *inst)
{
	int i, rv = 0;

	inst->dma_chan = dma_request_slave_channel(inst->dev, "rx-tx");

	inst->dma_config.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
	inst->dma_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
	inst->dma_config.src_addr = inst->smi_regs_busaddr + SMID;
	inst->dma_config.dst_addr = inst->dma_config.src_addr;
	/* Direction unimportant - always overridden by prep_slave_sg */
	inst->dma_config.direction = DMA_DEV_TO_MEM;
	dmaengine_slave_config(inst->dma_chan, &inst->dma_config);
	/* Alloc and map bounce buffers */
	for (i = 0; i < DMA_BOUNCE_BUFFER_COUNT; ++i) {
		inst->bounce.buffer[i] =
		dmam_alloc_coherent(inst->dev, DMA_BOUNCE_BUFFER_SIZE,
				&inst->bounce.phys[i],
				GFP_KERNEL);
		if (!inst->bounce.buffer[i]) {
			dev_err(inst->dev, "Could not allocate buffer!");
			rv = -ENOMEM;
			break;
		}
		smi_scatterlist_from_buffer(
			inst,
			inst->bounce.phys[i],
			DMA_BOUNCE_BUFFER_SIZE,
			&inst->bounce.sgl[i]
		);
	}

	return rv;
}

int nand_dma_config_start(__u32 rw, dma_addr_t addr,__u32 length)
{
	//int ret = 0;
	//int nents = 0;
	struct dma_slave_config dma_conf = {0};
	struct dma_async_tx_descriptor *dma_desc = NULL;

	dma_conf.direction = DMA_DEV_TO_MEM;
	dma_conf.src_addr = 0x01c03300;
	dma_conf.dst_addr = 0x01c03300;
	dma_conf.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
	dma_conf.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
	dma_conf.src_maxburst = 1;
	dma_conf.dst_maxburst = 1;
	dma_conf.slave_id = rw ? sunxi_slave_id(DRQDST_NAND0, DRQSRC_SDRAM) : sunxi_slave_id(DRQDST_SDRAM, DRQSRC_NAND0);
	dmaengine_slave_config(dma_hdl, &dma_conf);

	dma_desc = dmaengine_prep_slave_single(dma_hdl, addr, length,
				(rw ? DMA_TO_DEVICE : DMA_FROM_DEVICE), DMA_PREP_INTERRUPT|DMA_CTRL_ACK);
	if (!dma_desc) {
		printk("dmaengine prepare failed!\n");
		return -1;
	}

	dma_desc->callback = nand_dma_callback;
	dma_desc->callback_param = NULL;
	dmaengine_submit(dma_desc);

	dma_async_issue_pending(dma_hdl);

	return 0;
}

static struct dma_chan *sh_mobile_i2c_request_dma_chan(struct device *dev,
				enum dma_transfer_direction dir, dma_addr_t port_addr)
{
	struct dma_chan *chan;
	struct dma_slave_config cfg;
	char *chan_name = dir == DMA_MEM_TO_DEV ? "tx" : "rx";
	int ret;

	chan = dma_request_slave_channel_reason(dev, chan_name);
	if (IS_ERR(chan)) {
		dev_dbg(dev, "request_channel failed for %s (%ld)\n", chan_name,
			PTR_ERR(chan));
		return chan;
	}

	memset(&cfg, 0, sizeof(cfg));
	cfg.direction = dir;
	if (dir == DMA_MEM_TO_DEV) {
		cfg.dst_addr = port_addr;
		cfg.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
	} else {
		cfg.src_addr = port_addr;
		cfg.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
	}

	ret = dmaengine_slave_config(chan, &cfg);
	if (ret) {
		dev_dbg(dev, "slave_config failed for %s (%d)\n", chan_name, ret);
		dma_release_channel(chan);
		return ERR_PTR(ret);
	}

	dev_dbg(dev, "got DMA channel for %s\n", chan_name);
	return chan;
}

static void omap2_mcspi_tx_dma(struct spi_device *spi,
				struct spi_transfer *xfer,
				struct dma_slave_config cfg)
{
	struct omap2_mcspi	*mcspi;
	struct omap2_mcspi_dma  *mcspi_dma;

	mcspi = spi_master_get_devdata(spi->master);
	mcspi_dma = &mcspi->dma_channels[spi->chip_select];

	if (mcspi_dma->dma_tx) {
		struct dma_async_tx_descriptor *tx;

		dmaengine_slave_config(mcspi_dma->dma_tx, &cfg);

		tx = dmaengine_prep_slave_sg(mcspi_dma->dma_tx, xfer->tx_sg.sgl,
					     xfer->tx_sg.nents,
					     DMA_MEM_TO_DEV,
					     DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
		if (tx) {
			tx->callback = omap2_mcspi_tx_callback;
			tx->callback_param = spi;
			dmaengine_submit(tx);
		} else {
			/* FIXME: fall back to PIO? */
		}
	}
	dma_async_issue_pending(mcspi_dma->dma_tx);
	omap2_mcspi_set_dma_req(spi, 0, 1);

}