serial: samsung: add DMA support for RX

Add RX DMA transfers support for samsung serial driver. It's enabled
when DMA controller for RX channel is specified in device-tree.

DMA transactions are started when number of bytes in RX FIFO reaches
trigger level, otherwise PIO mode is used. DMA transfer size is always
PAGE_SIZE which can cause large latency when smaller data amount is
transferred, so we always terminate DMA transaction on RX timeout
interrupt. Timeout interval is set to 64 frame times.

Based on previous work of Sylwester Nawrocki and Lukasz Czerwinski.

Signed-off-by: Robert Baldyga <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/samsung.c

···
 
 #define S3C24XX_TX_PIO			1
 #define S3C24XX_TX_DMA			2
+#define S3C24XX_RX_PIO			1
+#define S3C24XX_RX_DMA			2
 /* macros to change one thing to another */
 
 #define tx_enabled(port) ((port)->unused[0])
···
 	}
 }
 
+static void s3c24xx_uart_copy_rx_to_tty(struct s3c24xx_uart_port *ourport,
+		struct tty_port *tty, int count)
+{
+	struct s3c24xx_uart_dma *dma = ourport->dma;
+	int copied;
+
+	if (!count)
+		return;
+
+	dma_sync_single_for_cpu(ourport->port.dev, dma->rx_addr,
+				dma->rx_size, DMA_FROM_DEVICE);
+
+	ourport->port.icount.rx += count;
+	if (!tty) {
+		dev_err(ourport->port.dev, "No tty port\n");
+		return;
+	}
+	copied = tty_insert_flip_string(tty,
+			((unsigned char *)(ourport->dma->rx_buf)), count);
+	if (copied != count) {
+		WARN_ON(1);
+		dev_err(ourport->port.dev, "RxData copy to tty layer failed\n");
+	}
+}
+
+static int s3c24xx_serial_rx_fifocnt(struct s3c24xx_uart_port *ourport,
+				     unsigned long ufstat);
+
+static void uart_rx_drain_fifo(struct s3c24xx_uart_port *ourport)
+{
+	struct uart_port *port = &ourport->port;
+	struct tty_port *tty = &port->state->port;
+	unsigned int ch, ufstat;
+	unsigned int count;
+
+	ufstat = rd_regl(port, S3C2410_UFSTAT);
+	count = s3c24xx_serial_rx_fifocnt(ourport, ufstat);
+
+	if (!count)
+		return;
+
+	while (count-- > 0) {
+		ch = rd_regb(port, S3C2410_URXH);
+
+		ourport->port.icount.rx++;
+		tty_insert_flip_char(tty, ch, TTY_NORMAL);
+	}
+
+	tty_flip_buffer_push(tty);
+}
+
 static void s3c24xx_serial_stop_rx(struct uart_port *port)
 {
 	struct s3c24xx_uart_port *ourport = to_ourport(port);
+	struct s3c24xx_uart_dma *dma = ourport->dma;
+	struct tty_port *t = &port->state->port;
+	struct dma_tx_state state;
+	enum dma_status dma_status;
+	unsigned int received;
 
 	if (rx_enabled(port)) {
 		dbg("s3c24xx_serial_stop_rx: port=%p\n", port);
···
 		else
 			disable_irq_nosync(ourport->rx_irq);
 		rx_enabled(port) = 0;
+	}
+	if (dma && dma->rx_chan) {
+		dmaengine_pause(dma->tx_chan);
+		dma_status = dmaengine_tx_status(dma->rx_chan,
+				dma->rx_cookie, &state);
+		if (dma_status == DMA_IN_PROGRESS ||
+			dma_status == DMA_PAUSED) {
+			received = dma->rx_bytes_requested - state.residue;
+			dmaengine_terminate_all(dma->rx_chan);
+			s3c24xx_uart_copy_rx_to_tty(ourport, t, received);
+		}
 	}
 }
 
···
 	return (ufstat & info->rx_fifomask) >> info->rx_fifoshift;
 }
 
+static void s3c64xx_start_rx_dma(struct s3c24xx_uart_port *ourport);
+static void s3c24xx_serial_rx_dma_complete(void *args)
+{
+	struct s3c24xx_uart_port *ourport = args;
+	struct uart_port *port = &ourport->port;
+
+	struct s3c24xx_uart_dma *dma = ourport->dma;
+	struct tty_port *t = &port->state->port;
+	struct tty_struct *tty = tty_port_tty_get(&ourport->port.state->port);
+
+	struct dma_tx_state state;
+	unsigned long flags;
+	int received;
+
+	dmaengine_tx_status(dma->rx_chan,  dma->rx_cookie, &state);
+	received  = dma->rx_bytes_requested - state.residue;
+	async_tx_ack(dma->rx_desc);
+
+	spin_lock_irqsave(&port->lock, flags);
+
+	if (received)
+		s3c24xx_uart_copy_rx_to_tty(ourport, t, received);
+
+	if (tty) {
+		tty_flip_buffer_push(t);
+		tty_kref_put(tty);
+	}
+
+	s3c64xx_start_rx_dma(ourport);
+
+	spin_unlock_irqrestore(&port->lock, flags);
+}
+
+static void s3c64xx_start_rx_dma(struct s3c24xx_uart_port *ourport)
+{
+	struct s3c24xx_uart_dma *dma = ourport->dma;
+
+	dma_sync_single_for_device(ourport->port.dev, dma->rx_addr,
+				dma->rx_size, DMA_FROM_DEVICE);
+
+	dma->rx_desc = dmaengine_prep_slave_single(dma->rx_chan,
+				dma->rx_addr, dma->rx_size, DMA_DEV_TO_MEM,
+				DMA_PREP_INTERRUPT);
+	if (!dma->rx_desc) {
+		dev_err(ourport->port.dev, "Unable to get desc for Rx\n");
+		return;
+	}
+
+	dma->rx_desc->callback = s3c24xx_serial_rx_dma_complete;
+	dma->rx_desc->callback_param = ourport;
+	dma->rx_bytes_requested = dma->rx_size;
+
+	dma->rx_cookie = dmaengine_submit(dma->rx_desc);
+	dma_async_issue_pending(dma->rx_chan);
+}
 
 /* ? - where has parity gone?? */
 #define S3C2410_UERSTAT_PARITY (0x1000)
 
-static irqreturn_t
-s3c24xx_serial_rx_chars(int irq, void *dev_id)
+static void enable_rx_dma(struct s3c24xx_uart_port *ourport)
+{
+	struct uart_port *port = &ourport->port;
+	unsigned int ucon;
+
+	/* set Rx mode to DMA mode */
+	ucon = rd_regl(port, S3C2410_UCON);
+	ucon &= ~(S3C64XX_UCON_RXBURST_MASK |
+			S3C64XX_UCON_TIMEOUT_MASK |
+			S3C64XX_UCON_EMPTYINT_EN |
+			S3C64XX_UCON_DMASUS_EN |
+			S3C64XX_UCON_TIMEOUT_EN |
+			S3C64XX_UCON_RXMODE_MASK);
+	ucon |= S3C64XX_UCON_RXBURST_16 |
+			0xf << S3C64XX_UCON_TIMEOUT_SHIFT |
+			S3C64XX_UCON_EMPTYINT_EN |
+			S3C64XX_UCON_TIMEOUT_EN |
+			S3C64XX_UCON_RXMODE_DMA;
+	wr_regl(port, S3C2410_UCON, ucon);
+
+	ourport->rx_mode = S3C24XX_RX_DMA;
+}
+
+static void enable_rx_pio(struct s3c24xx_uart_port *ourport)
+{
+	struct uart_port *port = &ourport->port;
+	unsigned int ucon;
+
+	/* set Rx mode to DMA mode */
+	ucon = rd_regl(port, S3C2410_UCON);
+	ucon &= ~(S3C64XX_UCON_TIMEOUT_MASK |
+			S3C64XX_UCON_EMPTYINT_EN |
+			S3C64XX_UCON_DMASUS_EN |
+			S3C64XX_UCON_TIMEOUT_EN |
+			S3C64XX_UCON_RXMODE_MASK);
+	ucon |= 0xf << S3C64XX_UCON_TIMEOUT_SHIFT |
+			S3C64XX_UCON_TIMEOUT_EN |
+			S3C64XX_UCON_RXMODE_CPU;
+	wr_regl(port, S3C2410_UCON, ucon);
+
+	ourport->rx_mode = S3C24XX_RX_PIO;
+}
+
+static irqreturn_t s3c24xx_serial_rx_chars_dma(int irq, void *dev_id)
+{
+	unsigned int utrstat, ufstat, received;
+	struct s3c24xx_uart_port *ourport = dev_id;
+	struct uart_port *port = &ourport->port;
+	struct s3c24xx_uart_dma *dma = ourport->dma;
+	struct tty_struct *tty = tty_port_tty_get(&ourport->port.state->port);
+	struct tty_port *t = &port->state->port;
+	unsigned long flags;
+	struct dma_tx_state state;
+
+	utrstat = rd_regl(port, S3C2410_UTRSTAT);
+	ufstat = rd_regl(port, S3C2410_UFSTAT);
+
+	spin_lock_irqsave(&port->lock, flags);
+
+	if (!(utrstat & S3C2410_UTRSTAT_TIMEOUT)) {
+		s3c64xx_start_rx_dma(ourport);
+		if (ourport->rx_mode == S3C24XX_RX_PIO)
+			enable_rx_dma(ourport);
+		goto finish;
+	}
+
+	if (ourport->rx_mode == S3C24XX_RX_DMA) {
+		dmaengine_pause(dma->rx_chan);
+		dmaengine_tx_status(dma->rx_chan, dma->rx_cookie, &state);
+		dmaengine_terminate_all(dma->rx_chan);
+		received = dma->rx_bytes_requested - state.residue;
+		s3c24xx_uart_copy_rx_to_tty(ourport, t, received);
+
+		enable_rx_pio(ourport);
+	}
+
+	uart_rx_drain_fifo(ourport);
+
+	if (tty) {
+		tty_flip_buffer_push(t);
+		tty_kref_put(tty);
+	}
+
+	wr_regl(port, S3C2410_UTRSTAT, S3C2410_UTRSTAT_TIMEOUT);
+
+finish:
+	spin_unlock_irqrestore(&port->lock, flags);
+
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t s3c24xx_serial_rx_chars_pio(int irq, void *dev_id)
 {
 	struct s3c24xx_uart_port *ourport = dev_id;
 	struct uart_port *port = &ourport->port;
···
 
 out:
 	return IRQ_HANDLED;
+}
+
+
+static irqreturn_t s3c24xx_serial_rx_chars(int irq, void *dev_id)
+{
+	struct s3c24xx_uart_port *ourport = dev_id;
+
+	if (ourport->dma && ourport->dma->rx_chan)
+		return s3c24xx_serial_rx_chars_dma(irq, dev_id);
+	return s3c24xx_serial_rx_chars_pio(irq, dev_id);
 }
 
 static irqreturn_t s3c24xx_serial_tx_chars(int irq, void *id)
···
 static int s3c64xx_serial_startup(struct uart_port *port)
 {
 	struct s3c24xx_uart_port *ourport = to_ourport(port);
+	unsigned long flags;
+	unsigned int ufcon;
 	int ret;
 
 	dbg("s3c64xx_serial_startup: port=%p (%08llx,%p)\n",
···
 	spin_lock_irqsave(&port->lock, flags);
 
 	ufcon = rd_regl(port, S3C2410_UFCON);
-	ufcon |= S3C2410_UFCON_RESETRX | S3C2410_UFCON_RESETTX;
+	ufcon |= S3C2410_UFCON_RESETRX | S3C2410_UFCON_RESETTX |
+			S5PV210_UFCON_RXTRIG8;
 	wr_regl(port, S3C2410_UFCON, ufcon);
 
 	enable_rx_pio(ourport);

drivers/tty/serial/samsung.h

···
 
 	unsigned int			tx_in_progress;
 	unsigned int			tx_mode;
+	unsigned int			rx_mode;
 
 	struct s3c24xx_uart_info	*info;
 	struct clk			*clk;