serial: imx: add DMA support for imx6q

We only enable the DMA support when the following are meet:

  [1] The uart port supports the hardware flow control(CTS/RTS).
      (Some uart port does not support the CTS/RTS.)

  [2] The application enables the CTS/RTS.

  [3] The Soc is imx6q.
      For the sdma's firmware limit, we do not support the DMA except
      the imx6q platform.

  [4] The uart is not used as a console.
Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -48,9 +48,11 @@
 #include <linux/of.h>
 #include <linux/of_device.h>
 #include <linux/io.h>
+#include <linux/dma-mapping.h>
 
 #include <asm/irq.h>
 #include <linux/platform_data/serial-imx.h>
+#include <linux/platform_data/dma-imx.h>
 
 /* Register definitions */
 #define URXD0 0x0  /* Receiver Register */
@@ -82,6 +84,7 @@
 #define UCR1_ADBR	(1<<14) /* Auto detect baud rate */
 #define UCR1_TRDYEN	(1<<13) /* Transmitter ready interrupt enable */
 #define UCR1_IDEN	(1<<12) /* Idle condition interrupt */
+#define UCR1_ICD_REG(x) (((x) & 3) << 10) /* idle condition detect */
 #define UCR1_RRDYEN	(1<<9)	/* Recv ready interrupt enable */
 #define UCR1_RDMAEN	(1<<8)	/* Recv ready DMA enable */
 #define UCR1_IREN	(1<<7)	/* Infrared interface enable */
@@ -90,6 +93,7 @@
 #define UCR1_SNDBRK	(1<<4)	/* Send break */
 #define UCR1_TDMAEN	(1<<3)	/* Transmitter ready DMA enable */
 #define IMX1_UCR1_UARTCLKEN (1<<2) /* UART clock enabled, i.mx1 only */
+#define UCR1_ATDMAEN    (1<<2)  /* Aging DMA Timer Enable */
 #define UCR1_DOZE	(1<<1)	/* Doze */
 #define UCR1_UARTEN	(1<<0)	/* UART enabled */
 #define UCR2_ESCI	(1<<15)	/* Escape seq interrupt enable */
@@ -125,6 +129,7 @@
 #define UCR4_ENIRI	(1<<8)	/* Serial infrared interrupt enable */
 #define UCR4_WKEN	(1<<7)	/* Wake interrupt enable */
 #define UCR4_REF16	(1<<6)	/* Ref freq 16 MHz */
+#define UCR4_IDDMAEN    (1<<6)  /* DMA IDLE Condition Detected */
 #define UCR4_IRSC	(1<<5)	/* IR special case */
 #define UCR4_TCEN	(1<<3)	/* Transmit complete interrupt enable */
 #define UCR4_BKEN	(1<<2)	/* Break condition interrupt enable */
@@ -209,6 +214,19 @@ struct imx_port {
 	struct clk		*clk_ipg;
 	struct clk		*clk_per;
 	const struct imx_uart_data *devdata;
+
+	/* DMA fields */
+	unsigned int		dma_is_inited:1;
+	unsigned int		dma_is_enabled:1;
+	unsigned int		dma_is_rxing:1;
+	unsigned int		dma_is_txing:1;
+	struct dma_chan		*dma_chan_rx, *dma_chan_tx;
+	struct scatterlist	rx_sgl, tx_sgl[2];
+	void			*rx_buf;
+	unsigned int		rx_bytes, tx_bytes;
+	struct work_struct	tsk_dma_rx, tsk_dma_tx;
+	unsigned int		dma_tx_nents;
+	wait_queue_head_t	dma_wait;
 };
 
 struct imx_port_ucrs {
@@ -399,6 +417,13 @@ static void imx_stop_tx(struct uart_port *port)
 		return;
 	}
 
+	/*
+	 * We are maybe in the SMP context, so if the DMA TX thread is running
+	 * on other cpu, we have to wait for it to finish.
+	 */
+	if (sport->dma_is_enabled && sport->dma_is_txing)
+		return;
+
 	temp = readl(sport->port.membase + UCR1);
 	writel(temp & ~UCR1_TXMPTYEN, sport->port.membase + UCR1);
 }
@@ -411,6 +436,13 @@ static void imx_stop_rx(struct uart_port *port)
 	struct imx_port *sport = (struct imx_port *)port;
 	unsigned long temp;
 
+	/*
+	 * We are maybe in the SMP context, so if the DMA TX thread is running
+	 * on other cpu, we have to wait for it to finish.
+	 */
+	if (sport->dma_is_enabled && sport->dma_is_rxing)
+		return;
+
 	temp = readl(sport->port.membase + UCR2);
 	writel(temp & ~UCR2_RXEN, sport->port.membase + UCR2);
 }
@@ -446,6 +478,95 @@ static inline void imx_transmit_buffer(struct imx_port *sport)
 		imx_stop_tx(&sport->port);
 }
 
+static void dma_tx_callback(void *data)
+{
+	struct imx_port *sport = data;
+	struct scatterlist *sgl = &sport->tx_sgl[0];
+	struct circ_buf *xmit = &sport->port.state->xmit;
+	unsigned long flags;
+
+	dma_unmap_sg(sport->port.dev, sgl, sport->dma_tx_nents, DMA_TO_DEVICE);
+
+	sport->dma_is_txing = 0;
+
+	/* update the stat */
+	spin_lock_irqsave(&sport->port.lock, flags);
+	xmit->tail = (xmit->tail + sport->tx_bytes) & (UART_XMIT_SIZE - 1);
+	sport->port.icount.tx += sport->tx_bytes;
+	spin_unlock_irqrestore(&sport->port.lock, flags);
+
+	dev_dbg(sport->port.dev, "we finish the TX DMA.\n");
+
+	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+		uart_write_wakeup(&sport->port);
+
+	if (waitqueue_active(&sport->dma_wait)) {
+		wake_up(&sport->dma_wait);
+		dev_dbg(sport->port.dev, "exit in %s.\n", __func__);
+		return;
+	}
+
+	schedule_work(&sport->tsk_dma_tx);
+}
+
+static void dma_tx_work(struct work_struct *w)
+{
+	struct imx_port *sport = container_of(w, struct imx_port, tsk_dma_tx);
+	struct circ_buf *xmit = &sport->port.state->xmit;
+	struct scatterlist *sgl = sport->tx_sgl;
+	struct dma_async_tx_descriptor *desc;
+	struct dma_chan	*chan = sport->dma_chan_tx;
+	struct device *dev = sport->port.dev;
+	enum dma_status status;
+	unsigned long flags;
+	int ret;
+
+	status = chan->device->device_tx_status(chan, (dma_cookie_t)0, NULL);
+	if (DMA_IN_PROGRESS == status)
+		return;
+
+	spin_lock_irqsave(&sport->port.lock, flags);
+	sport->tx_bytes = uart_circ_chars_pending(xmit);
+	if (sport->tx_bytes == 0) {
+		spin_unlock_irqrestore(&sport->port.lock, flags);
+		return;
+	}
+
+	if (xmit->tail > xmit->head) {
+		sport->dma_tx_nents = 2;
+		sg_init_table(sgl, 2);
+		sg_set_buf(sgl, xmit->buf + xmit->tail,
+				UART_XMIT_SIZE - xmit->tail);
+		sg_set_buf(sgl + 1, xmit->buf, xmit->head);
+	} else {
+		sport->dma_tx_nents = 1;
+		sg_init_one(sgl, xmit->buf + xmit->tail, sport->tx_bytes);
+	}
+	spin_unlock_irqrestore(&sport->port.lock, flags);
+
+	ret = dma_map_sg(dev, sgl, sport->dma_tx_nents, DMA_TO_DEVICE);
+	if (ret == 0) {
+		dev_err(dev, "DMA mapping error for TX.\n");
+		return;
+	}
+	desc = dmaengine_prep_slave_sg(chan, sgl, sport->dma_tx_nents,
+					DMA_MEM_TO_DEV, DMA_PREP_INTERRUPT);
+	if (!desc) {
+		dev_err(dev, "We cannot prepare for the TX slave dma!\n");
+		return;
+	}
+	desc->callback = dma_tx_callback;
+	desc->callback_param = sport;
+
+	dev_dbg(dev, "TX: prepare to send %lu bytes by DMA.\n",
+			uart_circ_chars_pending(xmit));
+	/* fire it */
+	sport->dma_is_txing = 1;
+	dmaengine_submit(desc);
+	dma_async_issue_pending(chan);
+	return;
+}
+
 /*
  * interrupts disabled on entry
  */
@@ -472,8 +593,10 @@ static void imx_start_tx(struct uart_port *port)
 	temp |= UCR4_OREN;
 	writel(temp, sport->port.membase + UCR4);
 
-	temp = readl(sport->port.membase + UCR1);
-	writel(temp | UCR1_TXMPTYEN, sport->port.membase + UCR1);
+	if (!sport->dma_is_enabled) {
+		temp = readl(sport->port.membase + UCR1);
+		writel(temp | UCR1_TXMPTYEN, sport->port.membase + UCR1);
+	}
 
 	if (USE_IRDA(sport)) {
 		temp = readl(sport->port.membase + UCR1);
@@ -485,6 +608,15 @@ static void imx_start_tx(struct uart_port *port)
 		writel(temp, sport->port.membase + UCR4);
 	}
 
+	if (sport->dma_is_enabled) {
+		/*
+		 * We may in the interrupt context, so arise a work_struct to
+		 * do the real job.
+		 */
+		schedule_work(&sport->tsk_dma_tx);
+		return;
+	}
+
 	if (readl(sport->port.membase + uts_reg(sport)) & UTS_TXEMPTY)
 		imx_transmit_buffer(sport);
 }
@@ -600,6 +732,28 @@ static irqreturn_t imx_rxint(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
+/*
+ * If the RXFIFO is filled with some data, and then we
+ * arise a DMA operation to receive them.
+ */
+static void imx_dma_rxint(struct imx_port *sport)
+{
+	unsigned long temp;
+
+	temp = readl(sport->port.membase + USR2);
+	if ((temp & USR2_RDR) && !sport->dma_is_rxing) {
+		sport->dma_is_rxing = 1;
+
+		/* disable the `Recerver Ready Interrrupt` */
+		temp = readl(sport->port.membase + UCR1);
+		temp &= ~(UCR1_RRDYEN);
+		writel(temp, sport->port.membase + UCR1);
+
+		/* tell the DMA to receive the data. */
+		schedule_work(&sport->tsk_dma_rx);
+	}
+}
+
 static irqreturn_t imx_int(int irq, void *dev_id)
 {
 	struct imx_port *sport = dev_id;
@@ -608,8 +762,12 @@ static irqreturn_t imx_int(int irq, void *dev_id)
 
 	sts = readl(sport->port.membase + USR1);
 
-	if (sts & USR1_RRDY)
-		imx_rxint(irq, dev_id);
+	if (sts & USR1_RRDY) {
+		if (sport->dma_is_enabled)
+			imx_dma_rxint(sport);
+		else
+			imx_rxint(irq, dev_id);
+	}
 
 	if (sts & USR1_TRDY &&
 			readl(sport->port.membase + UCR1) & UCR1_TXMPTYEN)
@@ -666,7 +824,8 @@ static void imx_set_mctrl(struct uart_port *port, unsigned int mctrl)
 	temp = readl(sport->port.membase + UCR2) & ~UCR2_CTS;
 
 	if (mctrl & TIOCM_RTS)
-		temp |= UCR2_CTS;
+		if (!sport->dma_is_enabled)
+			temp |= UCR2_CTS;
 
 	writel(temp, sport->port.membase + UCR2);
 }
@@ -705,6 +864,226 @@ static int imx_setup_ufcr(struct imx_port *sport, unsigned int mode)
 	return 0;
 }
 
+#define RX_BUF_SIZE	(PAGE_SIZE)
+static int start_rx_dma(struct imx_port *sport);
+static void dma_rx_work(struct work_struct *w)
+{
+	struct imx_port *sport = container_of(w, struct imx_port, tsk_dma_rx);
+	struct tty_port *port = &sport->port.state->port;
+
+	if (sport->rx_bytes) {
+		tty_insert_flip_string(port, sport->rx_buf, sport->rx_bytes);
+		tty_flip_buffer_push(port);
+		sport->rx_bytes = 0;
+	}
+
+	if (sport->dma_is_rxing)
+		start_rx_dma(sport);
+}
+
+static void imx_rx_dma_done(struct imx_port *sport)
+{
+	unsigned long temp;
+
+	/* Enable this interrupt when the RXFIFO is empty. */
+	temp = readl(sport->port.membase + UCR1);
+	temp |= UCR1_RRDYEN;
+	writel(temp, sport->port.membase + UCR1);
+
+	sport->dma_is_rxing = 0;
+
+	/* Is the shutdown waiting for us? */
+	if (waitqueue_active(&sport->dma_wait))
+		wake_up(&sport->dma_wait);
+}
+
+/*
+ * There are three kinds of RX DMA interrupts(such as in the MX6Q):
+ *   [1] the RX DMA buffer is full.
+ *   [2] the Aging timer expires(wait for 8 bytes long)
+ *   [3] the Idle Condition Detect(enabled the UCR4_IDDMAEN).
+ *
+ * The [2] is trigger when a character was been sitting in the FIFO
+ * meanwhile [3] can wait for 32 bytes long when the RX line is
+ * on IDLE state and RxFIFO is empty.
+ */
+static void dma_rx_callback(void *data)
+{
+	struct imx_port *sport = data;
+	struct dma_chan	*chan = sport->dma_chan_rx;
+	struct scatterlist *sgl = &sport->rx_sgl;
+	struct dma_tx_state state;
+	enum dma_status status;
+	unsigned int count;
+
+	/* unmap it first */
+	dma_unmap_sg(sport->port.dev, sgl, 1, DMA_FROM_DEVICE);
+
+	status = chan->device->device_tx_status(chan, (dma_cookie_t)0, &state);
+	count = RX_BUF_SIZE - state.residue;
+	dev_dbg(sport->port.dev, "We get %d bytes.\n", count);
+
+	if (count) {
+		sport->rx_bytes = count;
+		schedule_work(&sport->tsk_dma_rx);
+	} else
+		imx_rx_dma_done(sport);
+}
+
+static int start_rx_dma(struct imx_port *sport)
+{
+	struct scatterlist *sgl = &sport->rx_sgl;
+	struct dma_chan	*chan = sport->dma_chan_rx;
+	struct device *dev = sport->port.dev;
+	struct dma_async_tx_descriptor *desc;
+	int ret;
+
+	sg_init_one(sgl, sport->rx_buf, RX_BUF_SIZE);
+	ret = dma_map_sg(dev, sgl, 1, DMA_FROM_DEVICE);
+	if (ret == 0) {
+		dev_err(dev, "DMA mapping error for RX.\n");
+		return -EINVAL;
+	}
+	desc = dmaengine_prep_slave_sg(chan, sgl, 1, DMA_DEV_TO_MEM,
+					DMA_PREP_INTERRUPT);
+	if (!desc) {
+		dev_err(dev, "We cannot prepare for the RX slave dma!\n");
+		return -EINVAL;
+	}
+	desc->callback = dma_rx_callback;
+	desc->callback_param = sport;
+
+	dev_dbg(dev, "RX: prepare for the DMA.\n");
+	dmaengine_submit(desc);
+	dma_async_issue_pending(chan);
+	return 0;
+}
+
+static void imx_uart_dma_exit(struct imx_port *sport)
+{
+	if (sport->dma_chan_rx) {
+		dma_release_channel(sport->dma_chan_rx);
+		sport->dma_chan_rx = NULL;
+
+		kfree(sport->rx_buf);
+		sport->rx_buf = NULL;
+	}
+
+	if (sport->dma_chan_tx) {
+		dma_release_channel(sport->dma_chan_tx);
+		sport->dma_chan_tx = NULL;
+	}
+
+	sport->dma_is_inited = 0;
+}
+
+static int imx_uart_dma_init(struct imx_port *sport)
+{
+	struct dma_slave_config slave_config;
+	struct device *dev = sport->port.dev;
+	int ret;
+
+	/* Prepare for RX : */
+	sport->dma_chan_rx = dma_request_slave_channel(dev, "rx");
+	if (!sport->dma_chan_rx) {
+		dev_dbg(dev, "cannot get the DMA channel.\n");
+		ret = -EINVAL;
+		goto err;
+	}
+
+	slave_config.direction = DMA_DEV_TO_MEM;
+	slave_config.src_addr = sport->port.mapbase + URXD0;
+	slave_config.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
+	slave_config.src_maxburst = RXTL;
+	ret = dmaengine_slave_config(sport->dma_chan_rx, &slave_config);
+	if (ret) {
+		dev_err(dev, "error in RX dma configuration.\n");
+		goto err;
+	}
+
+	sport->rx_buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!sport->rx_buf) {
+		dev_err(dev, "cannot alloc DMA buffer.\n");
+		ret = -ENOMEM;
+		goto err;
+	}
+	sport->rx_bytes = 0;
+
+	/* Prepare for TX : */
+	sport->dma_chan_tx = dma_request_slave_channel(dev, "tx");
+	if (!sport->dma_chan_tx) {
+		dev_err(dev, "cannot get the TX DMA channel!\n");
+		ret = -EINVAL;
+		goto err;
+	}
+
+	slave_config.direction = DMA_MEM_TO_DEV;
+	slave_config.dst_addr = sport->port.mapbase + URTX0;
+	slave_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
+	slave_config.dst_maxburst = TXTL;
+	ret = dmaengine_slave_config(sport->dma_chan_tx, &slave_config);
+	if (ret) {
+		dev_err(dev, "error in TX dma configuration.");
+		goto err;
+	}
+
+	sport->dma_is_inited = 1;
+
+	return 0;
+err:
+	imx_uart_dma_exit(sport);
+	return ret;
+}
+
+static void imx_enable_dma(struct imx_port *sport)
+{
+	unsigned long temp;
+	struct tty_port *port = &sport->port.state->port;
+
+	port->low_latency = 1;
+	INIT_WORK(&sport->tsk_dma_tx, dma_tx_work);
+	INIT_WORK(&sport->tsk_dma_rx, dma_rx_work);
+	init_waitqueue_head(&sport->dma_wait);
+
+	/* set UCR1 */
+	temp = readl(sport->port.membase + UCR1);
+	temp |= UCR1_RDMAEN | UCR1_TDMAEN | UCR1_ATDMAEN |
+		/* wait for 32 idle frames for IDDMA interrupt */
+		UCR1_ICD_REG(3);
+	writel(temp, sport->port.membase + UCR1);
+
+	/* set UCR4 */
+	temp = readl(sport->port.membase + UCR4);
+	temp |= UCR4_IDDMAEN;
+	writel(temp, sport->port.membase + UCR4);
+
+	sport->dma_is_enabled = 1;
+}
+
+static void imx_disable_dma(struct imx_port *sport)
+{
+	unsigned long temp;
+	struct tty_port *port = &sport->port.state->port;
+
+	/* clear UCR1 */
+	temp = readl(sport->port.membase + UCR1);
+	temp &= ~(UCR1_RDMAEN | UCR1_TDMAEN | UCR1_ATDMAEN);
+	writel(temp, sport->port.membase + UCR1);
+
+	/* clear UCR2 */
+	temp = readl(sport->port.membase + UCR2);
+	temp &= ~(UCR2_CTSC | UCR2_CTS);
+	writel(temp, sport->port.membase + UCR2);
+
+	/* clear UCR4 */
+	temp = readl(sport->port.membase + UCR4);
+	temp &= ~UCR4_IDDMAEN;
+	writel(temp, sport->port.membase + UCR4);
+
+	sport->dma_is_enabled = 0;
+	port->low_latency = 0;
+}
+
 /* half the RX buffer size */
 #define CTSTL 16
 
@@ -869,6 +1248,15 @@ static void imx_shutdown(struct uart_port *port)
 	unsigned long temp;
 	unsigned long flags;
 
+	if (sport->dma_is_enabled) {
+		/* We have to wait for the DMA to finish. */
+		wait_event(sport->dma_wait,
+			!sport->dma_is_rxing && !sport->dma_is_txing);
+		imx_stop_rx(port);
+		imx_disable_dma(sport);
+		imx_uart_dma_exit(sport);
+	}
+
 	spin_lock_irqsave(&sport->port.lock, flags);
 	temp = readl(sport->port.membase + UCR2);
 	temp &= ~(UCR2_TXEN);
@@ -955,6 +1343,11 @@ imx_set_termios(struct uart_port *port, struct ktermios *termios,
 		if (sport->have_rtscts) {
 			ucr2 &= ~UCR2_IRTS;
 			ucr2 |= UCR2_CTSC;
+
+			/* Can we enable the DMA support? */
+			if (is_imx6q_uart(sport) && !uart_console(port)
+				&& !sport->dma_is_inited)
+				imx_uart_dma_init(sport);
 		} else {
 			termios->c_cflag &= ~CRTSCTS;
 		}
@@ -1073,6 +1466,8 @@ imx_set_termios(struct uart_port *port, struct ktermios *termios,
 	if (UART_ENABLE_MS(&sport->port, termios->c_cflag))
 		imx_enable_ms(&sport->port);
 
+	if (sport->dma_is_inited && !sport->dma_is_enabled)
+		imx_enable_dma(sport);
 	spin_unlock_irqrestore(&sport->port.lock, flags);
 }