lkml.org 
[lkml]   [2008]   [Nov]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Date
    Subject[RFC 1/2] serial/8250.c: Change to singly linked handler chain.
    I posted this to linux-serial yesterday, but it has attracted no comment
    yet, so I'm submitting it to a wider audience.

    This is a prerequisite to the interesting patch 2/2. This boots and
    runs, but only on a single-port interrupt, so that's not very good
    testing. It's out here for style comments.

    This just converts the list of struct uart_8250_port attached to a single
    IRQ from doubly linked to singly. It should have no behavior differences.


    ---
    drivers/serial/8250.c | 93 +++++++++++++++++++++++++++----------------------
    1 files changed, 51 insertions(+), 42 deletions(-)

    diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
    index 18caa95..7f66335 100644
    --- a/drivers/serial/8250.c
    +++ b/drivers/serial/8250.c
    @@ -116,7 +116,7 @@ static unsigned int probe_rsa_count;
    struct uart_8250_port {
    struct uart_port port;
    struct timer_list timer; /* "no irq" timer */
    - struct list_head list; /* ports on this IRQ */
    + struct uart_8250_port *next; /* ports on this IRQ */
    unsigned short capabilities; /* port capabilities */
    unsigned short bugs; /* port bugs */
    unsigned int tx_loadsz; /* transmit fifo load size */
    @@ -146,7 +146,7 @@ struct uart_8250_port {

    struct irq_info {
    spinlock_t lock;
    - struct list_head *head;
    + struct uart_8250_port *head;
    };

    static struct irq_info irq_lists[NR_IRQS];
    @@ -1458,23 +1458,39 @@ serial8250_handle_port(struct uart_8250_port *up)
    *
    * This means we need to loop through all ports. checking that they
    * don't have an interrupt pending.
    + *
    + * Fencepost consideration: serial8250_handle_port only polls each
    + * interrupt source once; it does not itself loop until the port
    + * has deasserted the interrupt line. Therefore, it is necessary to
    + * loop here until each port has had its IIR read in the idle state.
    + * "end" points to the beginning of the most recent run of idle ports.
    + * It is NULL if the current port is not idle. The loop ends when we
    + * are about to check end again.
    */
    static irqreturn_t serial8250_interrupt(int irq, void *dev_id)
    {
    struct irq_info *i = dev_id;
    - struct list_head *l, *end = NULL;
    + struct uart_8250_port *up, *end = NULL;
    int pass_counter = 0, handled = 0;

    DEBUG_INTR("serial8250_interrupt(%d)...", irq);

    spin_lock(&i->lock);

    - l = i->head;
    + up = i->head;
    do {
    - struct uart_8250_port *up;
    unsigned int iir;

    - up = list_entry(l, struct uart_8250_port, list);
    + if (up == NULL) {
    + if (pass_counter++ > PASS_LIMIT) {
    + /* If we hit this, we're dead. */
    + printk(KERN_ERR "serial8250: too much work for "
    + "irq%d\n", irq);
    + break;
    + }
    + up = i->head;
    + continue;
    + }

    iir = serial_in(up, UART_IIR);
    if (!(iir & UART_IIR_NO_INT)) {
    @@ -1486,9 +1505,10 @@ static irqreturn_t serial8250_interrupt(int irq, void *dev_id)
    } else if (up->port.iotype == UPIO_DWAPB &&
    (iir & UART_IIR_BUSY) == UART_IIR_BUSY) {
    /* The DesignWare APB UART has an Busy Detect (0x07)
    - * interrupt meaning an LCR write attempt occured while the
    - * UART was busy. The interrupt must be cleared by reading
    - * the UART status register (USR) and the LCR re-written. */
    + * interrupt meaning an LCR write attempt occured
    + * while the UART was busy. The interrupt must
    + * be cleared by reading the UART status register
    + * (USR) and re-writing the LCR. */
    unsigned int status;
    status = *(volatile u32 *)up->port.private_data;
    serial_out(up, UART_LCR, up->lcr);
    @@ -1497,17 +1517,10 @@ static irqreturn_t serial8250_interrupt(int irq, void *dev_id)

    end = NULL;
    } else if (end == NULL)
    - end = l;
    + end = up;

    - l = l->next;
    -
    - if (l == i->head && pass_counter++ > PASS_LIMIT) {
    - /* If we hit this, we're dead. */
    - printk(KERN_ERR "serial8250: too much work for "
    - "irq%d\n", irq);
    - break;
    - }
    - } while (l != end);
    + up = up->next;
    + } while (up != end);

    spin_unlock(&i->lock);

    @@ -1525,39 +1538,35 @@ static irqreturn_t serial8250_interrupt(int irq, void *dev_id)
    */
    static void serial_do_unlink(struct irq_info *i, struct uart_8250_port *up)
    {
    + struct uart_8250_port *p, **pptr = &i->head;
    +
    spin_lock_irq(&i->lock);

    - if (!list_empty(i->head)) {
    - if (i->head == &up->list)
    - i->head = i->head->next;
    - list_del(&up->list);
    - } else {
    - BUG_ON(i->head != &up->list);
    - i->head = NULL;
    + while ((p = *pptr) != up) {
    + BUG_ON(p == NULL);
    + pptr = &p->next;
    }

    + *pptr = up->next;
    +
    spin_unlock_irq(&i->lock);
    }

    static int serial_link_irq_chain(struct uart_8250_port *up)
    {
    struct irq_info *i = irq_lists + up->port.irq;
    - int ret, irq_flags = up->port.flags & UPF_SHARE_IRQ ? IRQF_SHARED : 0;
    + int ret = 0;
    + struct uart_8250_port *head;

    spin_lock_irq(&i->lock);
    + up->next = head = i->head;
    + i->head = up;
    + spin_unlock_irq(&i->lock);

    - if (i->head) {
    - list_add(&up->list, i->head);
    - spin_unlock_irq(&i->lock);
    -
    - ret = 0;
    - } else {
    - INIT_LIST_HEAD(&up->list);
    - i->head = &up->list;
    - spin_unlock_irq(&i->lock);
    -
    + if (!head) {
    + int irq_flag = up->port.flags & UPF_SHARE_IRQ ? IRQF_SHARED : 0;
    ret = request_irq(up->port.irq, serial8250_interrupt,
    - irq_flags, "serial", i);
    + irq_flag, "serial", i);
    if (ret < 0)
    serial_do_unlink(i, up);
    }
    @@ -1570,8 +1579,8 @@ static void serial_unlink_irq_chain(struct uart_8250_port *up)
    struct irq_info *i = irq_lists + up->port.irq;

    BUG_ON(i->head == NULL);
    -
    - if (list_empty(i->head))
    + serial_do_unlink(i, up);
    + if (i->head == NULL);
    free_irq(up->port.irq, i);

    serial_do_unlink(i, up);
    --
    1.5.6.5

    \
     
     \ /
      Last update: 2008-11-14 22:27    [W:0.029 / U:62.460 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site