i2c: at91: add dma support

From: Ludovic Desroches <[email protected]>

Add dma support for Atmel TWI which is available on sam9x5 and later.

When using dma for reception, you have to read only n-2 bytes. The last two bytes are read manually. Don't doing this should cause to send the STOP command too late and then to get extra data in the receive register.

Signed-off-by Ludovic Desroches <[email protected]>

---
 drivers/i2c/busses/i2c-at91.c | 326 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 314 insertions(+), 12 deletions(-)

drivers/i2c/busses/i2c-at91.c +314 -12

index aa59a25..33219f8 100644
@@ -19,6 +19,8 @@
 
 #include <linux/clk.h>
 #include <linux/completion.h>
+#include <linux/dma-mapping.h>
+#include <linux/dmaengine.h>
 #include <linux/err.h>
 #include <linux/i2c.h>
 #include <linux/interrupt.h>

@@ -30,6 +32,8 @@
 #include <linux/platform_device.h>
 #include <linux/slab.h>
 
+#include <mach/at_hdmac.h>
+
 #define TWI_CLK_HZ		100000			/* max 400 Kbits/s */
 #define AT91_I2C_TIMEOUT	msecs_to_jiffies(100)	/* transfer timeout */
 

@@ -65,9 +69,21 @@
 #define	AT91_TWI_THR		0x0034	/* Transmit Holding Register */
 
 struct at91_twi_pdata {
-	unsigned	clk_max_div;
-	unsigned	clk_offset;
-	bool		has_unre_flag;
+	unsigned		clk_max_div;
+	unsigned		clk_offset;
+	bool			has_unre_flag;
+	bool			has_dma_support;
+	struct at_dma_slave	dma_slave;
+};
+
+struct at91_twi_dma {
+	struct dma_chan			*chan_rx;
+	struct dma_chan			*chan_tx;
+	struct scatterlist		sg;
+	struct dma_async_tx_descriptor	*data_desc;
+	enum dma_data_direction		direction;
+	bool				buf_mapped;
+	bool				xfer_in_progress;
 };
 
 struct at91_twi_dev {

@@ -79,10 +95,13 @@ struct at91_twi_dev {
 	size_t			buf_len;
 	struct i2c_msg		*msg;
 	int			irq;
+	unsigned		imr;
 	unsigned		transfer_status;
 	struct i2c_adapter	adapter;
 	unsigned		twi_cwgr_reg;
 	struct at91_twi_pdata	*pdata;
+	bool			use_dma;
+	struct at91_twi_dma	dma;
 };
 
 static unsigned at91_twi_read(struct at91_twi_dev *dev, unsigned reg)

@@ -98,7 +117,18 @@ static void at91_twi_write(struct at91_twi_dev *dev, unsigned reg, unsigned val)
 static void at91_disable_twi_interrupts(struct at91_twi_dev *dev)
 {
 	at91_twi_write(dev, AT91_TWI_IDR,
-		       AT91_TWI_TXCOMP | AT91_TWI_RXRDY | AT91_TWI_TXRDY);
+			AT91_TWI_TXCOMP | AT91_TWI_RXRDY | AT91_TWI_TXRDY);
+}
+
+static void at91_twi_irq_save(struct at91_twi_dev *dev)
+{
+	dev->imr = at91_twi_read(dev, AT91_TWI_IMR) & 0x7;
+	at91_disable_twi_interrupts(dev);
+}
+
+static void at91_twi_irq_restore(struct at91_twi_dev *dev)
+{
+	at91_twi_write(dev, AT91_TWI_IER, dev->imr);
 }
 
 static void at91_init_twi_bus(struct at91_twi_dev *dev)

@@ -137,6 +167,30 @@ static void __devinit at91_calc_twi_clock(struct at91_twi_dev *dev, int twi_clk)
 	dev_dbg(dev->dev, "cdiv %d ckdiv %d\n", cdiv, ckdiv);
 }
 
+static void at91_twi_dma_cleanup(struct at91_twi_dev *dev)
+{
+	struct at91_twi_dma *dma = &dev->dma;
+
+	at91_twi_irq_save(dev);
+
+	if (dma->xfer_in_progress) {
+		if (dma->direction == DMA_FROM_DEVICE)
+			dma->chan_rx->device->device_control(dma->chan_rx,
+				DMA_TERMINATE_ALL, 0);
+		else
+			dma->chan_tx->device->device_control(dma->chan_tx,
+				DMA_TERMINATE_ALL, 0);
+		dma->xfer_in_progress = false;
+	}
+	if (dma->buf_mapped) {
+		dma_unmap_single(dev->dev, sg_dma_address(&dma->sg),
+				 dev->buf_len, dma->direction);
+		dma->buf_mapped = false;
+	}
+
+	at91_twi_irq_restore(dev);
+}
+
 static void at91_twi_write_next_byte(struct at91_twi_dev *dev)
 {
 	if (dev->buf_len <= 0)

@@ -153,6 +207,65 @@ static void at91_twi_write_next_byte(struct at91_twi_dev *dev)
 	++dev->buf;
 }
 
+static void at91_twi_write_data_dma_callback(void *data)
+{
+	struct at91_twi_dev *dev = (struct at91_twi_dev *)data;
+
+	dma_unmap_single(dev->dev, sg_dma_address(&dev->dma.sg),
+			 dev->buf_len, DMA_TO_DEVICE);
+
+	at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_STOP);
+}
+
+static void at91_twi_write_data_dma(struct at91_twi_dev *dev)
+{
+	dma_addr_t dma_addr;
+	dma_cookie_t cookie;
+	struct dma_async_tx_descriptor *txdesc;
+	struct at91_twi_dma *dma = &dev->dma;
+	struct dma_chan *chan_tx = dma->chan_tx;
+
+	if (dev->buf_len <= 0)
+		return;
+
+	dma->direction = DMA_TO_DEVICE;
+
+	at91_twi_irq_save(dev);
+	dma_addr = dma_map_single(dev->dev, dev->buf, dev->buf_len,
+				  DMA_TO_DEVICE);
+	if (dma_mapping_error(dev->dev, dma_addr)) {
+		dev_err(dev->dev, "dma map failed\n");
+		return;
+	}
+	dma->buf_mapped = true;
+	at91_twi_irq_restore(dev);
+	sg_dma_len(&dma->sg) = dev->buf_len;
+	sg_dma_address(&dma->sg) = dma_addr;
+
+	txdesc = chan_tx->device->device_prep_slave_sg(chan_tx, &dma->sg,
+		1, DMA_TO_DEVICE, DMA_PREP_INTERRUPT | DMA_CTRL_ACK, NULL);
+	if (!txdesc) {
+		dev_err(dev->dev, "dma prep slave sg failed\n");
+		goto error;
+	}
+
+	txdesc->callback = at91_twi_write_data_dma_callback;
+	txdesc->callback_param = dev;
+
+	dma->xfer_in_progress = true;
+	cookie = txdesc->tx_submit(txdesc);
+	if (dma_submit_error(cookie)) {
+		dev_err(dev->dev, "dma submit error\n");
+		goto error;
+	}
+	dma->chan_tx->device->device_issue_pending(chan_tx);
+
+	return;
+
+error:
+	at91_twi_dma_cleanup(dev);
+}
+
 static void at91_twi_read_next_byte(struct at91_twi_dev *dev)
 {
 	if (dev->buf_len <= 0)

@@ -178,6 +291,66 @@ static void at91_twi_read_next_byte(struct at91_twi_dev *dev)
 	++dev->buf;
 }
 
+static void at91_twi_read_data_dma_callback(void *data)
+{
+	struct at91_twi_dev *dev = (struct at91_twi_dev *)data;
+
+	dma_unmap_single(dev->dev, sg_dma_address(&dev->dma.sg),
+			 dev->buf_len, DMA_FROM_DEVICE);
+
+	/* The last two bytes have to be read without using dma */
+	dev->buf += dev->buf_len - 2;
+	dev->buf_len = 2;
+	at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_RXRDY);
+}
+
+static void at91_twi_read_data_dma(struct at91_twi_dev *dev)
+{
+	dma_addr_t dma_addr;
+	dma_cookie_t cookie;
+	struct dma_async_tx_descriptor *rxdesc;
+	struct at91_twi_dma *dma = &dev->dma;
+	struct dma_chan *chan_rx = dma->chan_rx;
+
+	dma->direction = DMA_FROM_DEVICE;
+
+	/* Keep in mind that we won't use dma to read the last two bytes */
+	at91_twi_irq_save(dev);
+	dma_addr = dma_map_single(dev->dev, dev->buf, dev->buf_len - 2,
+				  DMA_FROM_DEVICE);
+	if (dma_mapping_error(dev->dev, dma_addr)) {
+		dev_err(dev->dev, "dma map failed\n");
+		return;
+	}
+	dma->buf_mapped = true;
+	at91_twi_irq_restore(dev);
+	dma->sg.dma_address = dma_addr;
+	sg_dma_len(&dma->sg) = dev->buf_len - 2;
+
+	rxdesc = chan_rx->device->device_prep_slave_sg(chan_rx, &dma->sg,
+		1, DMA_FROM_DEVICE, DMA_PREP_INTERRUPT | DMA_CTRL_ACK, NULL);
+	if (!rxdesc) {
+		dev_err(dev->dev, "dma prep slave sg failed\n");
+		goto error;
+	}
+
+	rxdesc->callback = at91_twi_read_data_dma_callback;
+	rxdesc->callback_param = dev;
+
+	dma->xfer_in_progress = true;
+	cookie = rxdesc->tx_submit(rxdesc);
+	if (dma_submit_error(cookie)) {
+		dev_err(dev->dev, "dma submit error\n");
+		goto error;
+	}
+	dma->chan_rx->device->device_issue_pending(dma->chan_rx);
+
+	return;
+
+error:
+	at91_twi_dma_cleanup(dev);
+}
+
 static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id)
 {
 	struct at91_twi_dev *dev = dev_id;

@@ -224,12 +397,36 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
 		if (dev->buf_len <= 1 && !(dev->msg->flags & I2C_M_RECV_LEN))
 			start_flags |= AT91_TWI_STOP;
 		at91_twi_write(dev, AT91_TWI_CR, start_flags);
-		at91_twi_write(dev, AT91_TWI_IER,
+		/*
+		 * When using dma, the last byte has to be read manually in
+		 * order to not send the stop command too late and then
+		 * to receive extra data. In practice, there are some issues
+		 * if you use the dma to read n-1 bytes because of latency.
+		 * Reading n-2 bytes with dma and the two last ones manually
+		 * seems to be the best solution.
+		 */
+		if (dev->use_dma && (dev->buf_len > 2)) {
+			at91_twi_read_data_dma(dev);
+			/*
+			 * It is important to enable TXCOMP irq here because
+			 * doing it only when transferring the last two bytes
+			 * will mask NACK errors since TXCOMP is set when a
+			 * NACK occurs.
+			 */
+			at91_twi_write(dev, AT91_TWI_IER,
+			       AT91_TWI_TXCOMP);
+		} else
+			at91_twi_write(dev, AT91_TWI_IER,
 			       AT91_TWI_TXCOMP | AT91_TWI_RXRDY);
 	} else {
-		at91_twi_write_next_byte(dev);
-		at91_twi_write(dev, AT91_TWI_IER,
-			       AT91_TWI_TXCOMP | AT91_TWI_TXRDY);
+		if (dev->use_dma) {
+			at91_twi_write_data_dma(dev);
+			at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_TXCOMP);
+		} else {
+			at91_twi_write_next_byte(dev);
+			at91_twi_write(dev, AT91_TWI_IER,
+				AT91_TWI_TXCOMP | AT91_TWI_TXRDY);
+		}
 	}
 
 	ret = wait_for_completion_interruptible_timeout(&dev->cmd_complete,

@@ -237,23 +434,31 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
 	if (ret == 0) {
 		dev_err(dev->dev, "controller timed out\n");
 		at91_init_twi_bus(dev);
-		return -ETIMEDOUT;
+		ret = -ETIMEDOUT;
+		goto error;
 	}
 	if (dev->transfer_status & AT91_TWI_NACK) {
 		dev_dbg(dev->dev, "received nack\n");
-		return -EREMOTEIO;
+		ret = -EREMOTEIO;
+		goto error;
 	}
 	if (dev->transfer_status & AT91_TWI_OVRE) {
 		dev_err(dev->dev, "overrun while reading\n");
-		return -EIO;
+		ret = -EIO;
+		goto error;
 	}
 	if (has_unre_flag && dev->transfer_status & AT91_TWI_UNRE) {
 		dev_err(dev->dev, "underrun while writing\n");
-		return -EIO;
+		ret = -EIO;
+		goto error;
 	}
 	dev_dbg(dev->dev, "transfer complete\n");
 
 	return 0;
+
+error:
+	at91_twi_dma_cleanup(dev);
+	return ret;
 }
 
 static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)

@@ -324,36 +529,42 @@ static struct at91_twi_pdata at91rm9200_config = {
 	.clk_max_div = 5,
 	.clk_offset = 3,
 	.has_unre_flag = true,
+	.has_dma_support = false,
 };
 
 static struct at91_twi_pdata at91sam9261_config = {
 	.clk_max_div = 5,
 	.clk_offset = 4,
 	.has_unre_flag = false,
+	.has_dma_support = false,
 };
 
 static struct at91_twi_pdata at91sam9260_config = {
 	.clk_max_div = 7,
 	.clk_offset = 4,
 	.has_unre_flag = false,
+	.has_dma_support = false,
 };
 
 static struct at91_twi_pdata at91sam9g20_config = {
 	.clk_max_div = 7,
 	.clk_offset = 4,
 	.has_unre_flag = false,
+	.has_dma_support = false,
 };
 
 static struct at91_twi_pdata at91sam9g10_config = {
 	.clk_max_div = 7,
 	.clk_offset = 4,
 	.has_unre_flag = false,
+	.has_dma_support = false,
 };
 
 static struct at91_twi_pdata at91sam9x5_config = {
 	.clk_max_div = 7,
 	.clk_offset = 4,
 	.has_unre_flag = false,
+	.has_dma_support = true,
 };
 
 static const struct platform_device_id at91_twi_devtypes[] = {

@@ -400,6 +611,90 @@ MODULE_DEVICE_TABLE(of, atmel_twi_dt_ids);
 #define atmel_twi_dt_ids NULL
 #endif
 
+static bool __devinit filter(struct dma_chan *chan, void *slave)
+{
+	struct at_dma_slave *sl = slave;
+
+	if (sl->dma_dev == chan->device->dev) {
+		chan->private = sl;
+		return true;
+	} else {
+		return false;
+	}
+}
+
+static int __devinit at91_twi_configure_dma(struct at91_twi_dev *dev, u32 phy_addr)
+{
+	int ret = 0;
+	struct at_dma_slave *sdata;
+	struct dma_slave_config slave_config;
+	struct at91_twi_dma *dma = &dev->dma;
+
+	sdata = &dev->pdata->dma_slave;
+
+	memset(&slave_config, 0, sizeof(slave_config));
+	slave_config.src_addr = (dma_addr_t)phy_addr + AT91_TWI_RHR;
+	slave_config.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
+	slave_config.src_maxburst = 1;
+	slave_config.dst_addr = (dma_addr_t)phy_addr + AT91_TWI_THR;
+	slave_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
+	slave_config.dst_maxburst = 1;
+	slave_config.device_fc = false;
+
+	if (sdata && sdata->dma_dev) {
+		dma_cap_mask_t mask;
+
+		dma_cap_zero(mask);
+		dma_cap_set(DMA_SLAVE, mask);
+		dma->chan_tx = dma_request_channel(mask, filter, sdata);
+		if (!dma->chan_tx) {
+			dev_err(dev->dev, "no DMA channel available for tx\n");
+			ret = -EBUSY;
+			goto error;
+		}
+		dma->chan_rx = dma_request_channel(mask, filter, sdata);
+		if (!dma->chan_rx) {
+			dev_err(dev->dev, "no DMA channel available for rx\n");
+			ret = -EBUSY;
+			goto error;
+		}
+	} else {
+		ret = -EINVAL;
+		goto error;
+	}
+
+	slave_config.direction = DMA_TO_DEVICE;
+	if (dmaengine_slave_config(dma->chan_tx, &slave_config)) {
+		dev_err(dev->dev, "failed to configure tx channel\n");
+		ret = -EINVAL;
+		goto error;
+	}
+
+	slave_config.direction = DMA_FROM_DEVICE;
+	if (dmaengine_slave_config(dma->chan_rx, &slave_config)) {
+		dev_err(dev->dev, "failed to configure rx channel\n");
+		ret = -EINVAL;
+		goto error;
+	}
+
+	sg_init_table(&dma->sg, 1);
+	dma->buf_mapped = false;
+	dma->xfer_in_progress = false;
+
+	dev_info(dev->dev, "using %s (tx) and %s (rx) for DMA transfers\n",
+		 dma_chan_name(dma->chan_tx), dma_chan_name(dma->chan_rx));
+
+	return ret;
+
+error:
+	dev_info(dev->dev, "can't use DMA\n");
+	if (dma->chan_rx)
+		dma_release_channel(dma->chan_rx);
+	if (dma->chan_tx)
+		dma_release_channel(dma->chan_tx);
+	return ret;
+}
+
 static struct at91_twi_pdata * __devinit at91_twi_get_driver_data(
 					struct platform_device *pdev)
 {

@@ -418,6 +713,7 @@ static int __devinit at91_twi_probe(struct platform_device *pdev)
 	struct at91_twi_dev *dev;
 	struct resource *mem;
 	int rc;
+	u32 phy_addr;
 
 	dev = devm_kzalloc(&pdev->dev, sizeof(*dev), GFP_KERNEL);
 	if (!dev)

@@ -428,6 +724,7 @@ static int __devinit at91_twi_probe(struct platform_device *pdev)
 	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	if (!mem)
 		return -ENODEV;
+	phy_addr = mem->start;
 
 	dev->pdata = at91_twi_get_driver_data(pdev);
 	if (!dev->pdata)

@@ -457,6 +754,11 @@ static int __devinit at91_twi_probe(struct platform_device *pdev)
 	}
 	clk_prepare_enable(dev->clk);
 
+	if (dev->pdata->has_dma_support) {
+		if (at91_twi_configure_dma(dev, phy_addr) == 0)
+			dev->use_dma = true;
+	}
+
 	at91_calc_twi_clock(dev, TWI_CLK_HZ);
 	at91_init_twi_bus(dev);