Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=1ecc26bd2789ddb253f61e182a61c776663fe44c
Commit:     1ecc26bd2789ddb253f61e182a61c776663fe44c
Parent:     dfa7f343e526f3595d8f1d99807d141ae0c08601
Author:     Remy Bohmer <[EMAIL PROTECTED]>
AuthorDate: Fri Feb 8 04:21:05 2008 -0800
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Fri Feb 8 09:22:37 2008 -0800

    atmel_serial: split the interrupt handler
    
    Split up the interrupt handler of the serial port into a interrupt top-half
    and a tasklet.
    
    The goal is to get the interrupt top-half as short as possible to minimize
    latencies on interrupts.  But the old code also does some calls in the
    interrupt handler that are not allowed on preempt-RT in IRQF_NODELAY 
context.
    This handler is executed in this context because of the interrupt sharing 
with
    the timer interrupt.  The timer interrupt on Preempt-RT runs in IRQF_NODELAY
    context.
    
    The tasklet takes care of handling control status changes, pushing incoming
    characters to the tty layer, handling break and other errors.  It also 
handles
    pushing TX data into the data register.
    
    Reading the complete receive queue is still done in the top-half because we
    never want to miss any incoming character.
    
    [EMAIL PROTECTED]: misc cleanups and simplifications]
    Signed-off-by: Remy Bohmer <[EMAIL PROTECTED]>
    Signed-off-by: Haavard Skinnemoen <[EMAIL PROTECTED]>
    Cc: Andrew Victor <[EMAIL PROTECTED]>
    Tested-by: Marc Pignat <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
 drivers/serial/atmel_serial.c |  245 +++++++++++++++++++++++++++++++---------
 1 files changed, 190 insertions(+), 55 deletions(-)

diff --git a/drivers/serial/atmel_serial.c b/drivers/serial/atmel_serial.c
index e06c6c8..f0f6ea3 100644
--- a/drivers/serial/atmel_serial.c
+++ b/drivers/serial/atmel_serial.c
@@ -103,6 +103,13 @@
 static int (*atmel_open_hook)(struct uart_port *);
 static void (*atmel_close_hook)(struct uart_port *);
 
+struct atmel_uart_char {
+       u16             status;
+       u16             ch;
+};
+
+#define ATMEL_SERIAL_RINGSIZE 1024
+
 /*
  * We wrap our port structure around the generic uart_port.
  */
@@ -111,6 +118,12 @@ struct atmel_uart_port {
        struct clk              *clk;           /* uart clock */
        unsigned short          suspended;      /* is port suspended? */
        int                     break_active;   /* break being received */
+
+       struct tasklet_struct   tasklet;
+       unsigned int            irq_status;
+       unsigned int            irq_status_prev;
+
+       struct circ_buf         rx_ring;
 };
 
 static struct atmel_uart_port atmel_ports[ATMEL_MAX_UART];
@@ -240,22 +253,42 @@ static void atmel_break_ctl(struct uart_port *port, int 
break_state)
 }
 
 /*
+ * Stores the incoming character in the ring buffer
+ */
+static void
+atmel_buffer_rx_char(struct uart_port *port, unsigned int status,
+                    unsigned int ch)
+{
+       struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;
+       struct circ_buf *ring = &atmel_port->rx_ring;
+       struct atmel_uart_char *c;
+
+       if (!CIRC_SPACE(ring->head, ring->tail, ATMEL_SERIAL_RINGSIZE))
+               /* Buffer overflow, ignore char */
+               return;
+
+       c = &((struct atmel_uart_char *)ring->buf)[ring->head];
+       c->status       = status;
+       c->ch           = ch;
+
+       /* Make sure the character is stored before we update head. */
+       smp_wmb();
+
+       ring->head = (ring->head + 1) & (ATMEL_SERIAL_RINGSIZE - 1);
+}
+
+/*
  * Characters received (called from interrupt handler)
  */
 static void atmel_rx_chars(struct uart_port *port)
 {
        struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;
-       struct tty_struct *tty = port->info->tty;
-       unsigned int status, ch, flg;
+       unsigned int status, ch;
 
        status = UART_GET_CSR(port);
        while (status & ATMEL_US_RXRDY) {
                ch = UART_GET_CHAR(port);
 
-               port->icount.rx++;
-
-               flg = TTY_NORMAL;
-
                /*
                 * note that the error handling code is
                 * out of the main execution path
@@ -263,17 +296,14 @@ static void atmel_rx_chars(struct uart_port *port)
                if (unlikely(status & (ATMEL_US_PARE | ATMEL_US_FRAME
                                       | ATMEL_US_OVRE | ATMEL_US_RXBRK)
                             || atmel_port->break_active)) {
+
                        /* clear error */
                        UART_PUT_CR(port, ATMEL_US_RSTSTA);
+
                        if (status & ATMEL_US_RXBRK
                            && !atmel_port->break_active) {
-                               /* ignore side-effect */
-                               status &= ~(ATMEL_US_PARE | ATMEL_US_FRAME);
-                               port->icount.brk++;
                                atmel_port->break_active = 1;
                                UART_PUT_IER(port, ATMEL_US_RXBRK);
-                               if (uart_handle_break(port))
-                                       goto ignore_char;
                        } else {
                                /*
                                 * This is either the end-of-break
@@ -286,52 +316,30 @@ static void atmel_rx_chars(struct uart_port *port)
                                status &= ~ATMEL_US_RXBRK;
                                atmel_port->break_active = 0;
                        }
-                       if (status & ATMEL_US_PARE)
-                               port->icount.parity++;
-                       if (status & ATMEL_US_FRAME)
-                               port->icount.frame++;
-                       if (status & ATMEL_US_OVRE)
-                               port->icount.overrun++;
-
-                       status &= port->read_status_mask;
-
-                       if (status & ATMEL_US_RXBRK)
-                               flg = TTY_BREAK;
-                       else if (status & ATMEL_US_PARE)
-                               flg = TTY_PARITY;
-                       else if (status & ATMEL_US_FRAME)
-                               flg = TTY_FRAME;
                }
 
-               if (uart_handle_sysrq_char(port, ch))
-                       goto ignore_char;
-
-               uart_insert_char(port, status, ATMEL_US_OVRE, ch, flg);
-
-ignore_char:
+               atmel_buffer_rx_char(port, status, ch);
                status = UART_GET_CSR(port);
        }
 
-       tty_flip_buffer_push(tty);
+       tasklet_schedule(&atmel_port->tasklet);
 }
 
 /*
- * Transmit characters (called from interrupt handler)
+ * Transmit characters (called from tasklet with TXRDY interrupt
+ * disabled)
  */
 static void atmel_tx_chars(struct uart_port *port)
 {
        struct circ_buf *xmit = &port->info->xmit;
 
-       if (port->x_char) {
+       if (port->x_char && UART_GET_CSR(port) & ATMEL_US_TXRDY) {
                UART_PUT_CHAR(port, port->x_char);
                port->icount.tx++;
                port->x_char = 0;
-               return;
        }
-       if (uart_circ_empty(xmit) || uart_tx_stopped(port)) {
-               atmel_stop_tx(port);
+       if (uart_circ_empty(xmit) || uart_tx_stopped(port))
                return;
-       }
 
        while (UART_GET_CSR(port) & ATMEL_US_TXRDY) {
                UART_PUT_CHAR(port, xmit->buf[xmit->tail]);
@@ -344,8 +352,8 @@ static void atmel_tx_chars(struct uart_port *port)
        if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
                uart_write_wakeup(port);
 
-       if (uart_circ_empty(xmit))
-               atmel_stop_tx(port);
+       if (!uart_circ_empty(xmit))
+               UART_PUT_IER(port, ATMEL_US_TXRDY);
 }
 
 /*
@@ -371,14 +379,18 @@ atmel_handle_receive(struct uart_port *port, unsigned int 
pending)
 }
 
 /*
- * transmit interrupt handler.
+ * transmit interrupt handler. (Transmit is IRQF_NODELAY safe)
  */
 static void
 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)
-               atmel_tx_chars(port);
+       if (pending & ATMEL_US_TXRDY) {
+               UART_PUT_IDR(port, ATMEL_US_TXRDY);
+               tasklet_schedule(&atmel_port->tasklet);
+       }
 }
 
 /*
@@ -388,18 +400,13 @@ static void
 atmel_handle_status(struct uart_port *port, unsigned int pending,
                    unsigned int status)
 {
-       /* TODO: All reads to CSR will clear these interrupts! */
-       if (pending & ATMEL_US_RIIC)
-               port->icount.rng++;
-       if (pending & ATMEL_US_DSRIC)
-               port->icount.dsr++;
-       if (pending & ATMEL_US_DCDIC)
-               uart_handle_dcd_change(port, !(status & ATMEL_US_DCD));
-       if (pending & ATMEL_US_CTSIC)
-               uart_handle_cts_change(port, !(status & ATMEL_US_CTS));
+       struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;
+
        if (pending & (ATMEL_US_RIIC | ATMEL_US_DSRIC | ATMEL_US_DCDIC
-                               | ATMEL_US_CTSIC))
-               wake_up_interruptible(&port->info->delta_msr_wait);
+                               | ATMEL_US_CTSIC)) {
+               atmel_port->irq_status = status;
+               tasklet_schedule(&atmel_port->tasklet);
+       }
 }
 
 /*
@@ -426,6 +433,114 @@ static irqreturn_t atmel_interrupt(int irq, void *dev_id)
        return IRQ_HANDLED;
 }
 
+static void atmel_rx_from_ring(struct uart_port *port)
+{
+       struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;
+       struct circ_buf *ring = &atmel_port->rx_ring;
+       unsigned int flg;
+       unsigned int status;
+
+       while (ring->head != ring->tail) {
+               struct atmel_uart_char c;
+
+               /* Make sure c is loaded after head. */
+               smp_rmb();
+
+               c = ((struct atmel_uart_char *)ring->buf)[ring->tail];
+
+               ring->tail = (ring->tail + 1) & (ATMEL_SERIAL_RINGSIZE - 1);
+
+               port->icount.rx++;
+               status = c.status;
+               flg = TTY_NORMAL;
+
+               /*
+                * note that the error handling code is
+                * out of the main execution path
+                */
+               if (unlikely(status & (ATMEL_US_PARE | ATMEL_US_FRAME
+                                      | ATMEL_US_OVRE | ATMEL_US_RXBRK))) {
+                       if (status & ATMEL_US_RXBRK) {
+                               /* ignore side-effect */
+                               status &= ~(ATMEL_US_PARE | ATMEL_US_FRAME);
+
+                               port->icount.brk++;
+                               if (uart_handle_break(port))
+                                       continue;
+                       }
+                       if (status & ATMEL_US_PARE)
+                               port->icount.parity++;
+                       if (status & ATMEL_US_FRAME)
+                               port->icount.frame++;
+                       if (status & ATMEL_US_OVRE)
+                               port->icount.overrun++;
+
+                       status &= port->read_status_mask;
+
+                       if (status & ATMEL_US_RXBRK)
+                               flg = TTY_BREAK;
+                       else if (status & ATMEL_US_PARE)
+                               flg = TTY_PARITY;
+                       else if (status & ATMEL_US_FRAME)
+                               flg = TTY_FRAME;
+               }
+
+
+               if (uart_handle_sysrq_char(port, c.ch))
+                       continue;
+
+               uart_insert_char(port, status, ATMEL_US_OVRE, c.ch, flg);
+       }
+
+       /*
+        * Drop the lock here since it might end up calling
+        * uart_start(), which takes the lock.
+        */
+       spin_unlock(&port->lock);
+       tty_flip_buffer_push(port->info->tty);
+       spin_lock(&port->lock);
+}
+
+/*
+ * tasklet handling tty stuff outside the interrupt handler.
+ */
+static void atmel_tasklet_func(unsigned long data)
+{
+       struct uart_port *port = (struct uart_port *)data;
+       struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;
+       unsigned int status;
+       unsigned int status_change;
+
+       /* The interrupt handler does not take the lock */
+       spin_lock(&port->lock);
+
+       atmel_tx_chars(port);
+
+       status = atmel_port->irq_status;
+       status_change = status ^ atmel_port->irq_status_prev;
+
+       if (status_change & (ATMEL_US_RI | ATMEL_US_DSR
+                               | ATMEL_US_DCD | ATMEL_US_CTS)) {
+               /* TODO: All reads to CSR will clear these interrupts! */
+               if (status_change & ATMEL_US_RI)
+                       port->icount.rng++;
+               if (status_change & ATMEL_US_DSR)
+                       port->icount.dsr++;
+               if (status_change & ATMEL_US_DCD)
+                       uart_handle_dcd_change(port, !(status & ATMEL_US_DCD));
+               if (status_change & ATMEL_US_CTS)
+                       uart_handle_cts_change(port, !(status & ATMEL_US_CTS));
+
+               wake_up_interruptible(&port->info->delta_msr_wait);
+
+               atmel_port->irq_status_prev = status;
+       }
+
+       atmel_rx_from_ring(port);
+
+       spin_unlock(&port->lock);
+}
+
 /*
  * Perform initialization and enable port for reception
  */
@@ -757,6 +872,11 @@ static void __devinit atmel_init_port(struct 
atmel_uart_port *atmel_port,
        port->mapbase   = pdev->resource[0].start;
        port->irq       = pdev->resource[1].start;
 
+       tasklet_init(&atmel_port->tasklet, atmel_tasklet_func,
+                       (unsigned long)port);
+
+       memset(&atmel_port->rx_ring, 0, sizeof(atmel_port->rx_ring));
+
        if (data->regs)
                /* Already mapped by setup code */
                port->membase = data->regs;
@@ -997,11 +1117,20 @@ static int atmel_serial_resume(struct platform_device 
*pdev)
 static int __devinit atmel_serial_probe(struct platform_device *pdev)
 {
        struct atmel_uart_port *port;
+       void *data;
        int ret;
 
+       BUILD_BUG_ON(!is_power_of_2(ATMEL_SERIAL_RINGSIZE));
+
        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;
+
        ret = uart_add_one_port(&atmel_uart, &port->uart);
        if (ret)
                goto err_add_port;
@@ -1012,6 +1141,9 @@ static int __devinit atmel_serial_probe(struct 
platform_device *pdev)
        return 0;
 
 err_add_port:
+       kfree(port->rx_ring.buf);
+       port->rx_ring.buf = NULL;
+err_alloc_ring:
        if (!atmel_is_console_port(&port->uart)) {
                clk_disable(port->clk);
                clk_put(port->clk);
@@ -1032,6 +1164,9 @@ static int __devexit atmel_serial_remove(struct 
platform_device *pdev)
 
        ret = uart_remove_one_port(&atmel_uart, port);
 
+       tasklet_kill(&atmel_port->tasklet);
+       kfree(atmel_port->rx_ring.buf);
+
        /* "port" is allocated statically, so we shouldn't free it */
 
        clk_disable(atmel_port->clk);
-
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