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Subject[PATCH -mm v4 7/9] atmel_serial: Add DMA support
Date
From: Chip Coldwell <coldwell@redhat.com>

This patch is based on the DMA-patch by Chip Coldwell for the
AT91/AT32 serial USARTS, with some tweaks to make it apply neatly on
top of the other patches in this series.

The RX and TX code has been moved to a tasklet and reworked a bit.
Instead of depending on the ENDRX and TIMEOUT bits in CSR, we simply
grab as much data as we can from the DMA buffers. I think this closes
a race where the ENDRX bit is set after we read CSR but before we read
RPR, although I haven't confirmed this.

Similarly, the two TX handlers (ENDTX and TXBUFE) have been combined
into one. Since the current code only uses a single TX buffer, there's
no point in handling those interrupts separately.

This also fixes a DMA sync bug in the original patch.

[linux@bohmer.net: rebased onto irq-splitup patch]
[hskinnemoen@atmel.com: moved to tasklet, fixed dma bug, misc cleanups]
Signed-off-by: Remy Bohmer <linux@bohmer.net>
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
---
drivers/serial/Kconfig | 15 ++
drivers/serial/atmel_serial.c | 393 ++++++++++++++++++++++++++++++++++++++---
2 files changed, 384 insertions(+), 24 deletions(-)
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index d7e1996..67bfbb0 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -380,6 +380,21 @@ config SERIAL_ATMEL_CONSOLE
console is the device which receives all kernel messages and
warnings and which allows logins in single user mode).

+config SERIAL_ATMEL_PDC
+ bool "Support DMA transfers on AT91 / AT32 serial port"
+ depends on SERIAL_ATMEL
+ default y
+ help
+ Say Y here if you wish to use the PDC to do DMA transfers to
+ and from the Atmel AT91 / AT32 serial port. In order to
+ actually use DMA transfers, make sure that the use_dma_tx
+ and use_dma_rx members in the atmel_uart_data struct is set
+ appropriately for each port.
+
+ Note that break and error handling currently doesn't work
+ properly when DMA is enabled. Make sure that ports where
+ this matters don't use DMA.
+
config SERIAL_ATMEL_TTYAT
bool "Install as device ttyATn instead of ttySn"
depends on SERIAL_ATMEL=y
diff --git a/drivers/serial/atmel_serial.c b/drivers/serial/atmel_serial.c
index 0e65e98..e4f9449 100644
--- a/drivers/serial/atmel_serial.c
+++ b/drivers/serial/atmel_serial.c
@@ -7,6 +7,8 @@
* Based on drivers/char/serial_sa1100.c, by Deep Blue Solutions Ltd.
* Based on drivers/char/serial.c, by Linus Torvalds, Theodore Ts'o.
*
+ * DMA support added by Chip Coldwell.
+ *
* 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
@@ -33,6 +35,7 @@
#include <linux/sysrq.h>
#include <linux/tty_flip.h>
#include <linux/platform_device.h>
+#include <linux/dma-mapping.h>
#include <linux/atmel_pdc.h>

#include <asm/io.h>
@@ -47,6 +50,10 @@

#include "atmel_serial.h"

+#define PDC_BUFFER_SIZE 512
+/* Revisit: We should calculate this based on the actual port settings */
+#define PDC_RX_TIMEOUT (3 * 10) /* 3 bytes */
+
#if defined(CONFIG_SERIAL_ATMEL_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
#define SUPPORT_SYSRQ
#endif
@@ -104,6 +111,13 @@
static int (*atmel_open_hook)(struct uart_port *);
static void (*atmel_close_hook)(struct uart_port *);

+struct atmel_dma_buffer {
+ unsigned char *buf;
+ dma_addr_t dma_addr;
+ size_t dma_size;
+ unsigned int ofs;
+};
+
struct atmel_uart_char {
u16 status;
u16 ch;
@@ -120,6 +134,13 @@ struct atmel_uart_port {
unsigned short suspended; /* is port suspended? */
int break_active; /* break being received */

+ short use_dma_rx; /* enable PDC receiver */
+ short pdc_rx_idx; /* current PDC RX buffer */
+ struct atmel_dma_buffer pdc_rx[2]; /* PDC receier */
+
+ short use_dma_tx; /* enable PDC transmitter */
+ struct atmel_dma_buffer pdc_tx; /* PDC transmitter */
+
struct tasklet_struct tasklet;
unsigned int irq_status;
unsigned int irq_status_prev;
@@ -129,10 +150,39 @@ struct atmel_uart_port {

static struct atmel_uart_port atmel_ports[ATMEL_MAX_UART];

+#define PDC_RX_BUF(port) &(port)->pdc_rx[(port)->pdc_rx_idx]
+#define PDC_RX_SWITCH(port) (port)->pdc_rx_idx = !(port)->pdc_rx_idx
+
#ifdef SUPPORT_SYSRQ
static struct console atmel_console;
#endif

+#ifdef CONFIG_SERIAL_ATMEL_PDC
+static bool atmel_use_dma_rx(struct uart_port *port)
+{
+ struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;
+
+ return atmel_port->use_dma_rx;
+}
+
+static bool atmel_use_dma_tx(struct uart_port *port)
+{
+ struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;
+
+ return atmel_port->use_dma_tx;
+}
+#else
+static bool atmel_use_dma_rx(struct uart_port *port)
+{
+ return false;
+}
+
+static bool atmel_use_dma_tx(struct uart_port *port)
+{
+ return false;
+}
+#endif
+
/*
* Return TIOCSER_TEMT when transmitter FIFO and Shift register is empty.
*/
@@ -214,7 +264,12 @@ static u_int atmel_get_mctrl(struct uart_port *port)
*/
static void atmel_stop_tx(struct uart_port *port)
{
- UART_PUT_IDR(port, ATMEL_US_TXRDY);
+ if (atmel_use_dma_tx(port)) {
+ /* disable PDC transmit */
+ UART_PUT_PTCR(port, ATMEL_PDC_TXTDIS);
+ UART_PUT_IDR(port, ATMEL_US_ENDTX | ATMEL_US_TXBUFE);
+ } else
+ UART_PUT_IDR(port, ATMEL_US_TXRDY);
}

/*
@@ -222,7 +277,17 @@ static void atmel_stop_tx(struct uart_port *port)
*/
static void atmel_start_tx(struct uart_port *port)
{
- UART_PUT_IER(port, ATMEL_US_TXRDY);
+ if (atmel_use_dma_tx(port)) {
+ if (UART_GET_PTSR(port) & ATMEL_PDC_TXTEN)
+ /* The transmitter is already running. Yes, we
+ really need this.*/
+ return;
+
+ UART_PUT_IER(port, ATMEL_US_ENDTX | ATMEL_US_TXBUFE);
+ /* re-enable PDC transmit */
+ UART_PUT_PTCR(port, ATMEL_PDC_TXTEN);
+ } else
+ UART_PUT_IER(port, ATMEL_US_TXRDY);
}

/*
@@ -230,7 +295,12 @@ static void atmel_start_tx(struct uart_port *port)
*/
static void atmel_stop_rx(struct uart_port *port)
{
- UART_PUT_IDR(port, ATMEL_US_RXRDY);
+ if (atmel_use_dma_rx(port)) {
+ /* disable PDC receive */
+ UART_PUT_PTCR(port, ATMEL_PDC_RXTDIS);
+ UART_PUT_IDR(port, ATMEL_US_ENDRX | ATMEL_US_TIMEOUT);
+ } else
+ UART_PUT_IDR(port, ATMEL_US_RXRDY);
}

/*
@@ -279,6 +349,27 @@ atmel_buffer_rx_char(struct uart_port *port, unsigned int status,
}

/*
+ * Deal with parity, framing and overrun errors.
+ */
+static void atmel_pdc_rxerr(struct uart_port *port, unsigned int status)
+{
+ /* clear error */
+ UART_PUT_CR(port, ATMEL_US_RSTSTA);
+
+ if (status & ATMEL_US_RXBRK) {
+ /* ignore side-effect */
+ status &= ~(ATMEL_US_PARE | ATMEL_US_FRAME);
+ port->icount.brk++;
+ }
+ if (status & ATMEL_US_PARE)
+ port->icount.parity++;
+ if (status & ATMEL_US_FRAME)
+ port->icount.frame++;
+ if (status & ATMEL_US_OVRE)
+ port->icount.overrun++;
+}
+
+/*
* Characters received (called from interrupt handler)
*/
static void atmel_rx_chars(struct uart_port *port)
@@ -365,6 +456,25 @@ atmel_handle_receive(struct uart_port *port, unsigned int pending)
{
struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;

+ if (atmel_use_dma_rx(port)) {
+ /*
+ * PDC receive. Just schedule the tasklet and let it
+ * figure out the details.
+ *
+ * TODO: We're not handling error flags correctly at
+ * the moment.
+ */
+ if (pending & (ATMEL_US_ENDRX | ATMEL_US_TIMEOUT)) {
+ UART_PUT_IDR(port, (ATMEL_US_ENDRX
+ | ATMEL_US_TIMEOUT));
+ tasklet_schedule(&atmel_port->tasklet);
+ }
+
+ if (pending & (ATMEL_US_RXBRK | ATMEL_US_OVRE |
+ ATMEL_US_FRAME | ATMEL_US_PARE))
+ atmel_pdc_rxerr(port, pending);
+ }
+
/* Interrupt receive */
if (pending & ATMEL_US_RXRDY)
atmel_rx_chars(port);
@@ -387,10 +497,18 @@ atmel_handle_transmit(struct uart_port *port, unsigned int pending)
{
struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;

- /* Interrupt transmit */
- if (pending & ATMEL_US_TXRDY) {
- UART_PUT_IDR(port, ATMEL_US_TXRDY);
- tasklet_schedule(&atmel_port->tasklet);
+ if (atmel_use_dma_tx(port)) {
+ /* PDC transmit */
+ if (pending & (ATMEL_US_ENDTX | ATMEL_US_TXBUFE)) {
+ UART_PUT_IDR(port, ATMEL_US_ENDTX | ATMEL_US_TXBUFE);
+ tasklet_schedule(&atmel_port->tasklet);
+ }
+ } else {
+ /* Interrupt transmit */
+ if (pending & ATMEL_US_TXRDY) {
+ UART_PUT_IDR(port, ATMEL_US_TXRDY);
+ tasklet_schedule(&atmel_port->tasklet);
+ }
}
}

@@ -418,20 +536,67 @@ static irqreturn_t atmel_interrupt(int irq, void *dev_id)
struct uart_port *port = dev_id;
unsigned int status, pending, pass_counter = 0;

- status = UART_GET_CSR(port);
- pending = status & UART_GET_IMR(port);
- while (pending) {
+ do {
+ status = UART_GET_CSR(port);
+ pending = status & UART_GET_IMR(port);
+ if (!pending)
+ break;
+
atmel_handle_receive(port, pending);
atmel_handle_status(port, pending, status);
atmel_handle_transmit(port, pending);
+ } while (pass_counter++ < ATMEL_ISR_PASS_LIMIT);

- if (pass_counter++ > ATMEL_ISR_PASS_LIMIT)
- break;
+ return IRQ_HANDLED;
+}

- status = UART_GET_CSR(port);
- pending = status & UART_GET_IMR(port);
+/*
+ * Called from tasklet with ENDTX and TXBUFE interrupts disabled.
+ */
+static void atmel_tx_dma(struct uart_port *port)
+{
+ struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;
+ struct circ_buf *xmit = &port->info->xmit;
+ struct atmel_dma_buffer *pdc = &atmel_port->pdc_tx;
+ int count;
+
+ xmit->tail += pdc->ofs;
+ if (xmit->tail >= SERIAL_XMIT_SIZE)
+ xmit->tail -= SERIAL_XMIT_SIZE;
+
+ port->icount.tx += pdc->ofs;
+ pdc->ofs = 0;
+
+ if (!uart_circ_empty(xmit)) {
+ /* more to transmit - setup next transfer */
+
+ /* disable PDC transmit */
+ UART_PUT_PTCR(port, ATMEL_PDC_TXTDIS);
+ dma_sync_single_for_device(port->dev,
+ pdc->dma_addr,
+ pdc->dma_size,
+ DMA_TO_DEVICE);
+
+ if (xmit->tail < xmit->head)
+ count = xmit->head - xmit->tail;
+ else
+ count = SERIAL_XMIT_SIZE - xmit->tail;
+ pdc->ofs = count;
+
+ UART_PUT_TPR(port, pdc->dma_addr + xmit->tail);
+ UART_PUT_TCR(port, count);
+ /* re-enable PDC transmit and interrupts */
+ UART_PUT_PTCR(port, ATMEL_PDC_TXTEN);
+ UART_PUT_IER(port, ATMEL_US_ENDTX | ATMEL_US_TXBUFE);
+ } else {
+ /* nothing left to transmit - disable the transmitter */
+
+ /* disable PDC transmit */
+ UART_PUT_PTCR(port, ATMEL_PDC_TXTDIS);
}
- return IRQ_HANDLED;
+
+ if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+ uart_write_wakeup(port);
}

static void atmel_rx_from_ring(struct uart_port *port)
@@ -502,6 +667,76 @@ static void atmel_rx_from_ring(struct uart_port *port)
spin_lock(&port->lock);
}

+static void atmel_rx_from_dma(struct uart_port *port)
+{
+ struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;
+ struct tty_struct *tty = port->info->tty;
+ struct atmel_dma_buffer *pdc;
+ int rx_idx = atmel_port->pdc_rx_idx;
+ unsigned int head;
+ unsigned int tail;
+ unsigned int count;
+
+ do {
+ /* Reset the UART timeout early so that we don't miss one */
+ UART_PUT_CR(port, ATMEL_US_STTTO);
+
+ pdc = &atmel_port->pdc_rx[rx_idx];
+ head = UART_GET_RPR(port) - pdc->dma_addr;
+ tail = pdc->ofs;
+
+ /* If the PDC has switched buffers, RPR won't contain
+ * any address within the current buffer. Since head
+ * is unsigned, we just need a one-way comparison to
+ * find out.
+ *
+ * In this case, we just need to consume the entire
+ * buffer and resubmit it for DMA. This will clear the
+ * ENDRX bit as well, so that we can safely re-enable
+ * all interrupts below.
+ */
+ if (head >= pdc->dma_size)
+ head = pdc->dma_size;
+
+ if (likely(head != tail)) {
+ dma_sync_single_for_cpu(port->dev, pdc->dma_addr,
+ pdc->dma_size, DMA_FROM_DEVICE);
+
+ count = head - tail;
+ tty_insert_flip_string(tty, pdc->buf + pdc->ofs, count);
+
+ dma_sync_single_for_device(port->dev, pdc->dma_addr,
+ pdc->dma_size, DMA_FROM_DEVICE);
+
+ port->icount.rx += count;
+ pdc->ofs = head;
+ }
+
+ /*
+ * If the current buffer is full, we need to check if
+ * the next one contains any additional data.
+ */
+ if (head >= pdc->dma_size) {
+ pdc->ofs = 0;
+ UART_PUT_RNPR(port, pdc->dma_addr);
+ UART_PUT_RNCR(port, pdc->dma_size);
+
+ rx_idx = !rx_idx;
+ atmel_port->pdc_rx_idx = rx_idx;
+ }
+ } while (head >= pdc->dma_size);
+
+ /*
+ * Drop the lock here since it might end up calling
+ * uart_start(), which takes the lock.
+ */
+ spin_unlock(&port->lock);
+ tty_flip_buffer_push(tty);
+ spin_lock(&port->lock);
+
+ UART_PUT_IER(port, ATMEL_US_ENDRX | ATMEL_US_TIMEOUT);
+}
+
/*
* tasklet handling tty stuff outside the interrupt handler.
*/
@@ -515,7 +750,10 @@ static void atmel_tasklet_func(unsigned long data)
/* The interrupt handler does not take the lock */
spin_lock(&port->lock);

- atmel_tx_chars(port);
+ if (atmel_use_dma_tx(port))
+ atmel_tx_dma(port);
+ else
+ atmel_tx_chars(port);

status = atmel_port->irq_status;
status_change = status ^ atmel_port->irq_status_prev;
@@ -537,7 +775,10 @@ static void atmel_tasklet_func(unsigned long data)
atmel_port->irq_status_prev = status;
}

- atmel_rx_from_ring(port);
+ if (atmel_use_dma_rx(port))
+ atmel_rx_from_dma(port);
+ else
+ atmel_rx_from_ring(port);

spin_unlock(&port->lock);
}
@@ -547,6 +788,7 @@ static void atmel_tasklet_func(unsigned long data)
*/
static int atmel_startup(struct uart_port *port)
{
+ struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;
int retval;

/*
@@ -567,6 +809,56 @@ static int atmel_startup(struct uart_port *port)
}

/*
+ * Initialize DMA (if necessary)
+ */
+ if (atmel_use_dma_rx(port)) {
+ int i;
+
+ for (i = 0; i < 2; i++) {
+ struct atmel_dma_buffer *pdc = &atmel_port->pdc_rx[i];
+
+ pdc->buf = kmalloc(PDC_BUFFER_SIZE, GFP_KERNEL);
+ if (pdc->buf == NULL) {
+ if (i != 0) {
+ dma_unmap_single(port->dev,
+ atmel_port->pdc_rx[0].dma_addr,
+ PDC_BUFFER_SIZE,
+ DMA_FROM_DEVICE);
+ kfree(atmel_port->pdc_rx[0].buf);
+ }
+ free_irq(port->irq, port);
+ return -ENOMEM;
+ }
+ pdc->dma_addr = dma_map_single(port->dev,
+ pdc->buf,
+ PDC_BUFFER_SIZE,
+ DMA_FROM_DEVICE);
+ pdc->dma_size = PDC_BUFFER_SIZE;
+ pdc->ofs = 0;
+ }
+
+ atmel_port->pdc_rx_idx = 0;
+
+ UART_PUT_RPR(port, atmel_port->pdc_rx[0].dma_addr);
+ UART_PUT_RCR(port, PDC_BUFFER_SIZE);
+
+ UART_PUT_RNPR(port, atmel_port->pdc_rx[1].dma_addr);
+ UART_PUT_RNCR(port, PDC_BUFFER_SIZE);
+ }
+ if (atmel_use_dma_tx(port)) {
+ struct atmel_dma_buffer *pdc = &atmel_port->pdc_tx;
+ struct circ_buf *xmit = &port->info->xmit;
+
+ pdc->buf = xmit->buf;
+ pdc->dma_addr = dma_map_single(port->dev,
+ pdc->buf,
+ SERIAL_XMIT_SIZE,
+ DMA_TO_DEVICE);
+ pdc->dma_size = SERIAL_XMIT_SIZE;
+ pdc->ofs = 0;
+ }
+
+ /*
* If there is a specific "open" function (to register
* control line interrupts)
*/
@@ -585,8 +877,18 @@ static int atmel_startup(struct uart_port *port)
/* enable xmit & rcvr */
UART_PUT_CR(port, ATMEL_US_TXEN | ATMEL_US_RXEN);

- /* enable receive only */
- UART_PUT_IER(port, ATMEL_US_RXRDY);
+ if (atmel_use_dma_rx(port)) {
+ /* set UART timeout */
+ UART_PUT_RTOR(port, PDC_RX_TIMEOUT);
+ UART_PUT_CR(port, ATMEL_US_STTTO);
+
+ UART_PUT_IER(port, ATMEL_US_ENDRX | ATMEL_US_TIMEOUT);
+ /* enable PDC controller */
+ UART_PUT_PTCR(port, ATMEL_PDC_RXTEN);
+ } else {
+ /* enable receive only */
+ UART_PUT_IER(port, ATMEL_US_RXRDY);
+ }

return 0;
}
@@ -596,6 +898,38 @@ static int atmel_startup(struct uart_port *port)
*/
static void atmel_shutdown(struct uart_port *port)
{
+ struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;
+ /*
+ * Ensure everything is stopped.
+ */
+ atmel_stop_rx(port);
+ atmel_stop_tx(port);
+
+ /*
+ * Shut-down the DMA.
+ */
+ if (atmel_use_dma_rx(port)) {
+ int i;
+
+ for (i = 0; i < 2; i++) {
+ struct atmel_dma_buffer *pdc = &atmel_port->pdc_rx[i];
+
+ dma_unmap_single(port->dev,
+ pdc->dma_addr,
+ pdc->dma_size,
+ DMA_FROM_DEVICE);
+ kfree(pdc->buf);
+ }
+ }
+ if (atmel_use_dma_tx(port)) {
+ struct atmel_dma_buffer *pdc = &atmel_port->pdc_tx;
+
+ dma_unmap_single(port->dev,
+ pdc->dma_addr,
+ pdc->dma_size,
+ DMA_TO_DEVICE);
+ }
+
/*
* Disable all interrupts, port and break condition.
*/
@@ -707,6 +1041,10 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
if (termios->c_iflag & (BRKINT | PARMRK))
port->read_status_mask |= ATMEL_US_RXBRK;

+ if (atmel_use_dma_rx(port))
+ /* need to enable error interrupts */
+ UART_PUT_IER(port, port->read_status_mask);
+
/*
* Characters to ignore
*/
@@ -892,6 +1230,11 @@ static void __devinit atmel_init_port(struct atmel_uart_port *atmel_port,
clk_enable(atmel_port->clk);
port->uartclk = clk_get_rate(atmel_port->clk);
}
+
+ atmel_port->use_dma_rx = data->use_dma_rx;
+ atmel_port->use_dma_tx = data->use_dma_tx;
+ if (atmel_use_dma_tx(port))
+ port->fifosize = PDC_BUFFER_SIZE;
}

/*
@@ -1126,11 +1469,13 @@ static int __devinit atmel_serial_probe(struct platform_device *pdev)
port = &atmel_ports[pdev->id];
atmel_init_port(port, pdev);

- ret = -ENOMEM;
- data = kmalloc(ATMEL_SERIAL_RINGSIZE, GFP_KERNEL);
- if (!data)
- goto err_alloc_ring;
- port->rx_ring.buf = data;
+ if (!atmel_use_dma_rx(&port->uart)) {
+ ret = -ENOMEM;
+ data = kmalloc(ATMEL_SERIAL_RINGSIZE, GFP_KERNEL);
+ if (!data)
+ goto err_alloc_ring;
+ port->rx_ring.buf = data;
+ }

ret = uart_add_one_port(&atmel_uart, &port->uart);
if (ret)
--
1.5.3.8


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