serial: 8250: Add support for dmaengine

Add support for dmaengine API. The drivers can implement the
struct uart_8250_dma member in struct uart_8250_port and
8250.c can take care of the rest.
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250.c

@@ -1269,7 +1269,9 @@ static void serial8250_start_tx(struct uart_port *port)
 	struct uart_8250_port *up =
 		container_of(port, struct uart_8250_port, port);
 
-	if (!(up->ier & UART_IER_THRI)) {
+	if (up->dma && !serial8250_tx_dma(up)) {
+		return;
+	} else if (!(up->ier & UART_IER_THRI)) {
 		up->ier |= UART_IER_THRI;
 		serial_port_out(port, UART_IER, up->ier);
 
@@ -1467,6 +1469,7 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
 	unsigned long flags;
 	struct uart_8250_port *up =
 		container_of(port, struct uart_8250_port, port);
+	int dma_err = 0;
 
 	if (iir & UART_IIR_NO_INT)
 		return 0;
@@ -1477,8 +1480,13 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
 
 	DEBUG_INTR("status = %x...", status);
 
-	if (status & (UART_LSR_DR | UART_LSR_BI))
-		status = serial8250_rx_chars(up, status);
+	if (status & (UART_LSR_DR | UART_LSR_BI)) {
+		if (up->dma)
+			dma_err = serial8250_rx_dma(up, iir);
+
+		if (!up->dma || dma_err)
+			status = serial8250_rx_chars(up, status);
+	}
 	serial8250_modem_status(up);
 	if (status & UART_LSR_THRE)
 		serial8250_tx_chars(up);
@@ -2120,6 +2128,18 @@ static int serial8250_startup(struct uart_port *port)
 	up->lsr_saved_flags = 0;
 	up->msr_saved_flags = 0;
 
+	/*
+	 * Request DMA channels for both RX and TX.
+	 */
+	if (up->dma) {
+		retval = serial8250_request_dma(up);
+		if (retval) {
+			pr_warn_ratelimited("ttyS%d - failed to request DMA\n",
+					    serial_index(port));
+			up->dma = NULL;
+		}
+	}
+
 	/*
 	 * Finally, enable interrupts.  Note: Modem status interrupts
 	 * are set via set_termios(), which will be occurring imminently
@@ -2153,6 +2173,9 @@ static void serial8250_shutdown(struct uart_port *port)
 	up->ier = 0;
 	serial_port_out(port, UART_IER, 0);
 
+	if (up->dma)
+		serial8250_release_dma(up);
+
 	spin_lock_irqsave(&port->lock, flags);
 	if (port->flags & UPF_FOURPORT) {
 		/* reset interrupts on the AST Fourport board */
@@ -3217,6 +3240,8 @@ int serial8250_register_8250_port(struct uart_8250_port *up)
 			uart->dl_read = up->dl_read;
 		if (up->dl_write)
 			uart->dl_write = up->dl_write;
+		if (up->dma)
+			uart->dma = up->dma;
 
 		if (serial8250_isa_config != NULL)
 			serial8250_isa_config(0, &uart->port,

drivers/tty/serial/8250/8250.h

@@ -12,6 +12,35 @@
  */
 
 #include <linux/serial_8250.h>
+#include <linux/dmaengine.h>
+
+struct uart_8250_dma {
+	dma_filter_fn		fn;
+	void			*rx_param;
+	void			*tx_param;
+
+	int			rx_chan_id;
+	int			tx_chan_id;
+
+	struct dma_slave_config	rxconf;
+	struct dma_slave_config	txconf;
+
+	struct dma_chan		*rxchan;
+	struct dma_chan		*txchan;
+
+	dma_addr_t		rx_addr;
+	dma_addr_t		tx_addr;
+
+	dma_cookie_t		rx_cookie;
+	dma_cookie_t		tx_cookie;
+
+	void			*rx_buf;
+
+	size_t			rx_size;
+	size_t			tx_size;
+
+	unsigned char		tx_running:1;
+};
 
 struct old_serial_port {
 	unsigned int uart;
@@ -142,3 +171,24 @@ static inline int is_omap1510_8250(struct uart_8250_port *pt)
 	return 0;
 }
 #endif
+
+#ifdef CONFIG_SERIAL_8250_DMA
+extern int serial8250_tx_dma(struct uart_8250_port *);
+extern int serial8250_rx_dma(struct uart_8250_port *, unsigned int iir);
+extern int serial8250_request_dma(struct uart_8250_port *);
+extern void serial8250_release_dma(struct uart_8250_port *);
+#else
+static inline int serial8250_tx_dma(struct uart_8250_port *p)
+{
+	return -1;
+}
+static inline int serial8250_rx_dma(struct uart_8250_port *p, unsigned int iir)
+{
+	return -1;
+}
+static inline int serial8250_request_dma(struct uart_8250_port *p)
+{
+	return -1;
+}
+static inline void serial8250_release_dma(struct uart_8250_port *p) { }
+#endif

drivers/tty/serial/8250/8250_dma.c

+/*
+ * 8250_dma.c - DMA Engine API support for 8250.c
+ *
+ * Copyright (C) 2013 Intel Corporation
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/serial_reg.h>
+#include <linux/dma-mapping.h>
+
+#include "8250.h"
+
+static void __dma_tx_complete(void *param)
+{
+	struct uart_8250_port	*p = param;
+	struct uart_8250_dma	*dma = p->dma;
+	struct circ_buf		*xmit = &p->port.state->xmit;
+
+	dma->tx_running = 0;
+
+	dma_sync_single_for_cpu(dma->txchan->device->dev, dma->tx_addr,
+				UART_XMIT_SIZE, DMA_TO_DEVICE);
+
+	xmit->tail += dma->tx_size;
+	xmit->tail &= UART_XMIT_SIZE - 1;
+	p->port.icount.tx += dma->tx_size;
+
+	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+		uart_write_wakeup(&p->port);
+
+	if (!uart_circ_empty(xmit) && !uart_tx_stopped(&p->port)) {
+		serial8250_tx_dma(p);
+		uart_write_wakeup(&p->port);
+	}
+}
+
+static void __dma_rx_complete(void *param)
+{
+	struct uart_8250_port	*p = param;
+	struct uart_8250_dma	*dma = p->dma;
+	struct tty_struct	*tty = p->port.state->port.tty;
+	struct dma_tx_state	state;
+
+	dma_sync_single_for_cpu(dma->rxchan->device->dev, dma->rx_addr,
+				dma->rx_size, DMA_FROM_DEVICE);
+
+	dmaengine_tx_status(dma->rxchan, dma->rx_cookie, &state);
+	dmaengine_terminate_all(dma->rxchan);
+
+	tty_insert_flip_string(tty, dma->rx_buf, dma->rx_size - state.residue);
+	p->port.icount.rx += dma->rx_size - state.residue;
+
+	tty_flip_buffer_push(tty);
+}
+
+int serial8250_tx_dma(struct uart_8250_port *p)
+{
+	struct uart_8250_dma		*dma = p->dma;
+	struct circ_buf			*xmit = &p->port.state->xmit;
+	struct dma_async_tx_descriptor	*desc;
+
+	if (dma->tx_running) {
+		uart_write_wakeup(&p->port);
+		return -EBUSY;
+	}
+
+	dma->tx_size = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
+
+	desc = dmaengine_prep_slave_single(dma->txchan,
+					   dma->tx_addr + xmit->tail,
+					   dma->tx_size, DMA_MEM_TO_DEV,
+					   DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
+	if (!desc)
+		return -EBUSY;
+
+	dma->tx_running = 1;
+
+	desc->callback = __dma_tx_complete;
+	desc->callback_param = p;
+
+	dma->tx_cookie = dmaengine_submit(desc);
+
+	dma_sync_single_for_device(dma->txchan->device->dev, dma->tx_addr,
+				   UART_XMIT_SIZE, DMA_TO_DEVICE);
+
+	dma_async_issue_pending(dma->txchan);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(serial8250_tx_dma);
+
+int serial8250_rx_dma(struct uart_8250_port *p, unsigned int iir)
+{
+	struct uart_8250_dma		*dma = p->dma;
+	struct dma_async_tx_descriptor	*desc;
+	struct dma_tx_state		state;
+	int				dma_status;
+
+	/*
+	 * If RCVR FIFO trigger level was not reached, complete the transfer and
+	 * let 8250.c copy the remaining data.
+	 */
+	if ((iir & 0x3f) == UART_IIR_RX_TIMEOUT) {
+		dma_status = dmaengine_tx_status(dma->rxchan, dma->rx_cookie,
+						&state);
+		if (dma_status == DMA_IN_PROGRESS) {
+			dmaengine_pause(dma->rxchan);
+			__dma_rx_complete(p);
+		}
+		return -ETIMEDOUT;
+	}
+
+	desc = dmaengine_prep_slave_single(dma->rxchan, dma->rx_addr,
+					   dma->rx_size, DMA_DEV_TO_MEM,
+					   DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
+	if (!desc)
+		return -EBUSY;
+
+	desc->callback = __dma_rx_complete;
+	desc->callback_param = p;
+
+	dma->rx_cookie = dmaengine_submit(desc);
+
+	dma_sync_single_for_device(dma->rxchan->device->dev, dma->rx_addr,
+				   dma->rx_size, DMA_FROM_DEVICE);
+
+	dma_async_issue_pending(dma->rxchan);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(serial8250_rx_dma);
+
+int serial8250_request_dma(struct uart_8250_port *p)
+{
+	struct uart_8250_dma	*dma = p->dma;
+	dma_cap_mask_t		mask;
+
+	dma->rxconf.src_addr = p->port.mapbase + UART_RX;
+	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_channel(mask, dma->fn, dma->rx_param);
+	if (!dma->rxchan)
+		return -ENODEV;
+
+	dmaengine_slave_config(dma->rxchan, &dma->rxconf);
+
+	/* Get a channel for TX */
+	dma->txchan = dma_request_channel(mask, dma->fn, dma->tx_param);
+	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;
+}
+EXPORT_SYMBOL_GPL(serial8250_request_dma);
+
+void serial8250_release_dma(struct uart_8250_port *p)
+{
+	struct uart_8250_dma *dma = p->dma;
+
+	if (!dma)
+		return;
+
+	/* Release RX resources */
+	dmaengine_terminate_all(dma->rxchan);
+	dma_free_coherent(dma->rxchan->device->dev, dma->rx_size, dma->rx_buf,
+			  dma->rx_addr);
+	dma_release_channel(dma->rxchan);
+	dma->rxchan = NULL;
+
+	/* Release TX resources */
+	dmaengine_terminate_all(dma->txchan);
+	dma_unmap_single(dma->txchan->device->dev, dma->tx_addr,
+			 UART_XMIT_SIZE, DMA_TO_DEVICE);
+	dma_release_channel(dma->txchan);
+	dma->txchan = NULL;
+	dma->tx_running = 0;
+
+	dev_dbg_ratelimited(p->port.dev, "dma channels released\n");
+}
+EXPORT_SYMBOL_GPL(serial8250_release_dma);

drivers/tty/serial/8250/Kconfig

@@ -84,6 +84,14 @@ config SERIAL_8250_GSC
 	depends on SERIAL_8250 && GSC
 	default SERIAL_8250
 
+config SERIAL_8250_DMA
+	bool "DMA support for 16550 compatible UART controllers" if EXPERT
+	depends on SERIAL_8250 && DMADEVICES=y
+	default SERIAL_8250
+	help
+	  This builds DMA support that can be used with 8250/16650
+	  compatible UART controllers that support DMA signaling.
+
 config SERIAL_8250_PCI
 	tristate "8250/16550 PCI device support" if EXPERT
 	depends on SERIAL_8250 && PCI

drivers/tty/serial/8250/Makefile

@@ -5,6 +5,7 @@
 obj-$(CONFIG_SERIAL_8250)		+= 8250_core.o
 8250_core-y				:= 8250.o
 8250_core-$(CONFIG_SERIAL_8250_PNP)	+= 8250_pnp.o
+8250_core-$(CONFIG_SERIAL_8250_DMA)	+= 8250_dma.o
 obj-$(CONFIG_SERIAL_8250_GSC)		+= 8250_gsc.o
 obj-$(CONFIG_SERIAL_8250_PCI)		+= 8250_pci.o
 obj-$(CONFIG_SERIAL_8250_HP300)		+= 8250_hp300.o

include/linux/serial_8250.h

@@ -59,6 +59,8 @@ enum {
 	PLAT8250_DEV_SM501,
 };
 
+struct uart_8250_dma;
+
 /*
  * This should be used by drivers which want to register
  * their own 8250 ports without registering their own
@@ -91,6 +93,8 @@ struct uart_8250_port {
 #define MSR_SAVE_FLAGS UART_MSR_ANY_DELTA
 	unsigned char		msr_saved_flags;
 
+	struct uart_8250_dma	*dma;
+
 	/* 8250 specific callbacks */
 	int			(*dl_read)(struct uart_8250_port *);
 	void			(*dl_write)(struct uart_8250_port *, int);