atmel_serial: add DMA support

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]
[hskinnemoen@atmel.com: atmel_serial dma: Misc fixes and cleanups]
Signed-off-by: Remy Bohmer <linux@bohmer.net>
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Cc: Andrew Victor <linux@maxim.org.za>
Tested-by: Marc Pignat <marc.pignat@hevs.ch>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 383 insertions, 24 deletions

diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 84a054d7e986..b82595cf13e8 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 f0f6ea3a9eed..d15ab2243289 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 <linux/atmel_serial.h>
 
@@ -46,6 +49,10 @@
 #include <asm/arch/gpio.h>
 #endif
 
+#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
@@ -103,6 +110,13 @@
 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;
+        unsigned int    dma_size;
+        unsigned int    ofs;
+};
+
 struct atmel_uart_char {
         u16             status;
         u16             ch;
@@ -119,6 +133,13 @@ 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;
@@ -132,6 +153,32 @@ static struct atmel_uart_port atmel_ports[ATMEL_MAX_UART];
 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.
  */
@@ -213,7 +260,12 @@ 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);
 }
 
 /*
@@ -221,7 +273,17 @@ 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);
 }
 
 /*
@@ -229,7 +291,12 @@ 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);
 }
 
 /*
@@ -278,6 +345,27 @@ 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)
@@ -364,6 +452,25 @@ 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);
@@ -386,10 +493,18 @@ 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);
+                }
         }
 }
 
@@ -417,20 +532,63 @@ 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;
+        xmit->tail &= UART_XMIT_SIZE - 1;
+
+        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);
+
+                count = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
+                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)
@@ -501,6 +659,82 @@ 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.
+                 */
+                head = min(head, pdc->dma_size);
+
+                if (likely(head != tail)) {
+                        dma_sync_single_for_cpu(port->dev, pdc->dma_addr,
+                                        pdc->dma_size, DMA_FROM_DEVICE);
+
+                        /*
+                         * head will only wrap around when we recycle
+                         * the DMA buffer, and when that happens, we
+                         * explicitly set tail to 0. So head will
+                         * always be greater than tail.
+                         */
+                        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.
  */
@@ -514,7 +748,10 @@ 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;
@@ -536,7 +773,10 @@ 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);
 }
@@ -546,6 +786,7 @@ 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;
 
         /*
@@ -566,6 +807,56 @@ 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,
+                                               UART_XMIT_SIZE,
+                                               DMA_TO_DEVICE);
+                pdc->dma_size = UART_XMIT_SIZE;
+                pdc->ofs = 0;
+        }
+
+        /*
          * If there is a specific "open" function (to register
          * control line interrupts)
          */
@@ -584,8 +875,18 @@ 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;
 }
@@ -595,6 +896,38 @@ 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.
          */
@@ -706,6 +1039,10 @@ 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
          */
@@ -891,6 +1228,11 @@ 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;
 }
 
 /*
@@ -1125,11 +1467,13 @@ 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)