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Message-Id: <1197997575-13292-5-git-send-email-hskinnemoen@atmel.com>
Date: Tue, 18 Dec 2007 18:06:14 +0100
From: Haavard Skinnemoen <hskinnemoen@...el.com>
To: Andrew Victor <linux@...im.org.za>
Cc: Remy Bohmer <linux@...mer.net>,
ARM Linux Mailing List
<linux-arm-kernel@...ts.arm.linux.org.uk>,
Russell King - ARM Linux <linux@....linux.org.uk>,
linux-kernel@...r.kernel.org, kernel@...32linux.org,
Remy Bohmer <hskinnemoen@...el.com>
Subject: [PATCH 4/5] atmel_serial: Split the interrupt handler
From: Remy Bohmer <hskinnemoen@...el.com>
This patch splits 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.
The Transmit path was IRQF_NODELAY safe by itself, and is not adapted.
The read path for DMA(PDC) is also not adapted, because that code
does not run in IRQF_NODELAY context due to irq-sharing. The DBGU
which is shared with the timer-irq does not work with DMA, so
therefor this is no problem.
Reading the complete receive queue is still done in the top-half
because we never want to miss any incoming character.
[hskinnemoen@...el.com: misc cleanups and simplifications]
Signed-off-by: Remy Bohmer <linux@...mer.net>
Signed-off-by: Haavard Skinnemoen <hskinnemoen@...el.com>
---
drivers/serial/atmel_serial.c | 215 ++++++++++++++++++++++++++++++++---------
1 files changed, 169 insertions(+), 46 deletions(-)
diff --git a/drivers/serial/atmel_serial.c b/drivers/serial/atmel_serial.c
index a6b3828..990d3ab 100644
--- a/drivers/serial/atmel_serial.c
+++ b/drivers/serial/atmel_serial.c
@@ -111,6 +111,13 @@
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.
*/
@@ -119,6 +126,12 @@ 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_pending;
+ unsigned int irq_status;
+
+ struct circ_buf rx_ring;
};
static struct atmel_uart_port atmel_ports[ATMEL_MAX_UART];
@@ -248,22 +261,42 @@ 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
@@ -271,17 +304,14 @@ 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
@@ -294,33 +324,13 @@ 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);
}
/*
@@ -379,7 +389,7 @@ 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)
@@ -396,18 +406,16 @@ 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));
- if (pending & (ATMEL_US_RIIC | ATMEL_US_DSRIC | ATMEL_US_DCDIC
- | ATMEL_US_CTSIC))
- wake_up_interruptible(&port->info->delta_msr_wait);
+ struct atmel_uart_port *atmel_port = (struct atmel_uart_port *)port;
+
+ spin_lock(&port->lock);
+
+ atmel_port->irq_pending |= pending;
+ atmel_port->irq_status = status;
+
+ spin_unlock(&port->lock);
+
+ tasklet_schedule(&atmel_port->tasklet);
}
/*
@@ -434,6 +442,107 @@ 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);
+ }
+
+ tty_flip_buffer_push(port->info->tty);
+}
+
+/*
+ * 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 long flags;
+ unsigned int status;
+ unsigned int pending;
+
+ spin_lock_irqsave(&port->lock, flags);
+
+ if (atmel_port->irq_pending) {
+ pending = atmel_port->irq_pending;
+ status = atmel_port->irq_status;
+ atmel_port->irq_pending = 0;
+
+ spin_unlock_irqrestore(&port->lock, flags);
+
+ /* 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));
+ if (pending & (ATMEL_US_RIIC | ATMEL_US_DSRIC
+ | ATMEL_US_DCDIC | ATMEL_US_CTSIC))
+ wake_up_interruptible(&port->info->delta_msr_wait);
+ } else {
+ spin_unlock_irqrestore(&port->lock, flags);
+ }
+
+ atmel_rx_from_ring(port);
+}
+
/*
* Perform initialization and enable port for reception
*/
@@ -765,6 +874,11 @@ 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;
@@ -994,11 +1108,19 @@ 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);
+ data = kmalloc(ATMEL_SERIAL_RINGSIZE, GFP_KERNEL);
+ if (!data)
+ return -ENOMEM;
+ port->rx_ring.buf = data;
+
ret = uart_add_one_port(&atmel_uart, &port->uart);
if (!ret) {
device_init_wakeup(&pdev->dev, 1);
@@ -1022,6 +1144,7 @@ static int __devexit atmel_serial_remove(struct platform_device *pdev)
if (port) {
ret = uart_remove_one_port(&atmel_uart, port);
+ kfree(atmel_port->rx_ring.buf);
kfree(port);
}
--
1.5.3.4
--
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