1.1 --- a/xen/common/gdbstub.c	Thu Mar 23 15:53:52 2006 +0100
     1.2 +++ b/xen/common/gdbstub.c	Thu Mar 23 17:17:08 2006 +0100
     1.3 @@ -562,6 +562,7 @@ initialise_gdb(void)
     1.4      gdb_ctx->serhnd = serial_parse_handle(opt_gdb);
     1.5      if ( gdb_ctx->serhnd != -1 )
     1.6          printk("GDB stub initialised.\n");
     1.7 +    serial_start_sync(gdb_ctx->serhnd);
     1.8  }
     1.9  
    1.10  /*

     2.1 --- a/xen/drivers/char/ns16550.c	Thu Mar 23 15:53:52 2006 +0100
     2.2 +++ b/xen/drivers/char/ns16550.c	Thu Mar 23 17:17:08 2006 +0100
     2.3 @@ -121,8 +121,11 @@ static void ns16550_interrupt(
     2.4  
     2.5      while ( !(ns_read_reg(uart, IIR) & IIR_NOINT) )
     2.6      {
     2.7 -        serial_tx_interrupt(port, regs);
     2.8 -        serial_rx_interrupt(port, regs);
     2.9 +        char lsr = ns_read_reg(uart, LSR);
    2.10 +        if ( lsr & LSR_THRE )
    2.11 +            serial_tx_interrupt(port, regs);
    2.12 +        if ( lsr & LSR_DR )
    2.13 +            serial_rx_interrupt(port, regs);
    2.14      }
    2.15  }
    2.16  

     3.1 --- a/xen/drivers/char/serial.c	Thu Mar 23 15:53:52 2006 +0100
     3.2 +++ b/xen/drivers/char/serial.c	Thu Mar 23 17:17:08 2006 +0100
     3.3 @@ -7,6 +7,7 @@
     3.4   */
     3.5  
     3.6  #include <xen/config.h>
     3.7 +#include <xen/delay.h>
     3.8  #include <xen/init.h>
     3.9  #include <xen/irq.h>
    3.10  #include <xen/keyhandler.h> 
    3.11 @@ -15,8 +16,8 @@
    3.12  #include <xen/serial.h>
    3.13  
    3.14  static struct serial_port com[2] = {
    3.15 -    { .lock = SPIN_LOCK_UNLOCKED }, 
    3.16 -    { .lock = SPIN_LOCK_UNLOCKED }
    3.17 +    { .rx_lock = SPIN_LOCK_UNLOCKED, .tx_lock = SPIN_LOCK_UNLOCKED }, 
    3.18 +    { .rx_lock = SPIN_LOCK_UNLOCKED, .tx_lock = SPIN_LOCK_UNLOCKED }
    3.19  };
    3.20  
    3.21  void serial_rx_interrupt(struct serial_port *port, struct cpu_user_regs *regs)
    3.22 @@ -25,7 +26,7 @@ void serial_rx_interrupt(struct serial_p
    3.23      serial_rx_fn fn = NULL;
    3.24      unsigned long flags;
    3.25  
    3.26 -    spin_lock_irqsave(&port->lock, flags);
    3.27 +    spin_lock_irqsave(&port->rx_lock, flags);
    3.28  
    3.29      if ( port->driver->getc(port, &c) )
    3.30      {
    3.31 @@ -39,7 +40,7 @@ void serial_rx_interrupt(struct serial_p
    3.32              port->rxbuf[MASK_SERIAL_RXBUF_IDX(port->rxbufp++)] = c;            
    3.33      }
    3.34  
    3.35 -    spin_unlock_irqrestore(&port->lock, flags);
    3.36 +    spin_unlock_irqrestore(&port->rx_lock, flags);
    3.37  
    3.38      if ( fn != NULL )
    3.39          (*fn)(c & 0x7f, regs);
    3.40 @@ -50,7 +51,19 @@ void serial_tx_interrupt(struct serial_p
    3.41      int i;
    3.42      unsigned long flags;
    3.43  
    3.44 -    spin_lock_irqsave(&port->lock, flags);
    3.45 +    local_irq_save(flags);
    3.46 +
    3.47 +    /*
    3.48 +     * Avoid spinning for a long time: if there is a long-term lock holder
    3.49 +     * then we know that they'll be stuffing bytes into the transmitter which
    3.50 +     * will therefore not be empty for long.
    3.51 +     */
    3.52 +    while ( !spin_trylock(&port->tx_lock) )
    3.53 +    {
    3.54 +        if ( !port->driver->tx_empty(port) )
    3.55 +            return;
    3.56 +        cpu_relax();
    3.57 +    }
    3.58  
    3.59      if ( port->driver->tx_empty(port) )
    3.60      {
    3.61 @@ -63,7 +76,7 @@ void serial_tx_interrupt(struct serial_p
    3.62          }
    3.63      }
    3.64  
    3.65 -    spin_unlock_irqrestore(&port->lock, flags);
    3.66 +    spin_unlock_irqrestore(&port->tx_lock, flags);
    3.67  }
    3.68  
    3.69  static void __serial_putc(struct serial_port *port, char c)
    3.70 @@ -117,7 +130,7 @@ void serial_putc(int handle, char c)
    3.71      if ( (handle == -1) || !port->driver || !port->driver->putc )
    3.72          return;
    3.73  
    3.74 -    spin_lock_irqsave(&port->lock, flags);
    3.75 +    spin_lock_irqsave(&port->tx_lock, flags);
    3.76  
    3.77      if ( (c == '\n') && (handle & SERHND_COOKED) )
    3.78          __serial_putc(port, '\r');
    3.79 @@ -129,7 +142,7 @@ void serial_putc(int handle, char c)
    3.80  
    3.81      __serial_putc(port, c);
    3.82  
    3.83 -    spin_unlock_irqrestore(&port->lock, flags);
    3.84 +    spin_unlock_irqrestore(&port->tx_lock, flags);
    3.85  }
    3.86  
    3.87  void serial_puts(int handle, const char *s)
    3.88 @@ -141,7 +154,7 @@ void serial_puts(int handle, const char 
    3.89      if ( (handle == -1) || !port->driver || !port->driver->putc )
    3.90          return;
    3.91  
    3.92 -    spin_lock_irqsave(&port->lock, flags);
    3.93 +    spin_lock_irqsave(&port->tx_lock, flags);
    3.94  
    3.95      while ( (c = *s++) != '\0' )
    3.96      {
    3.97 @@ -156,7 +169,7 @@ void serial_puts(int handle, const char 
    3.98          __serial_putc(port, c);
    3.99      }
   3.100  
   3.101 -    spin_unlock_irqrestore(&port->lock, flags);
   3.102 +    spin_unlock_irqrestore(&port->tx_lock, flags);
   3.103  }
   3.104  
   3.105  char serial_getc(int handle)
   3.106 @@ -168,27 +181,28 @@ char serial_getc(int handle)
   3.107      if ( (handle == -1) || !port->driver || !port->driver->getc )
   3.108          return '\0';
   3.109  
   3.110 -    do {        
   3.111 +    do {
   3.112          for ( ; ; )
   3.113          {
   3.114 -            spin_lock_irqsave(&port->lock, flags);
   3.115 +            spin_lock_irqsave(&port->rx_lock, flags);
   3.116              
   3.117              if ( port->rxbufp != port->rxbufc )
   3.118              {
   3.119                  c = port->rxbuf[MASK_SERIAL_RXBUF_IDX(port->rxbufc++)];
   3.120 -                spin_unlock_irqrestore(&port->lock, flags);
   3.121 +                spin_unlock_irqrestore(&port->rx_lock, flags);
   3.122                  break;
   3.123              }
   3.124              
   3.125              if ( port->driver->getc(port, &c) )
   3.126              {
   3.127 -                spin_unlock_irqrestore(&port->lock, flags);
   3.128 +                spin_unlock_irqrestore(&port->rx_lock, flags);
   3.129                  break;
   3.130              }
   3.131  
   3.132 -            spin_unlock_irqrestore(&port->lock, flags);
   3.133 +            spin_unlock_irqrestore(&port->rx_lock, flags);
   3.134  
   3.135              cpu_relax();
   3.136 +            udelay(100);
   3.137          }
   3.138      } while ( ((handle & SERHND_LO) &&  (c & 0x80)) ||
   3.139                ((handle & SERHND_HI) && !(c & 0x80)) );
   3.140 @@ -241,7 +255,7 @@ void serial_set_rx_handler(int handle, s
   3.141      if ( handle == -1 )
   3.142          return;
   3.143  
   3.144 -    spin_lock_irqsave(&port->lock, flags);
   3.145 +    spin_lock_irqsave(&port->rx_lock, flags);
   3.146  
   3.147      if ( port->rx != NULL )
   3.148          goto fail;
   3.149 @@ -265,11 +279,11 @@ void serial_set_rx_handler(int handle, s
   3.150          port->rx = fn;
   3.151      }
   3.152  
   3.153 -    spin_unlock_irqrestore(&port->lock, flags);
   3.154 +    spin_unlock_irqrestore(&port->rx_lock, flags);
   3.155      return;
   3.156  
   3.157   fail:
   3.158 -    spin_unlock_irqrestore(&port->lock, flags);
   3.159 +    spin_unlock_irqrestore(&port->rx_lock, flags);
   3.160      printk("ERROR: Conflicting receive handlers for COM%d\n", 
   3.161             handle & SERHND_IDX);
   3.162  }
   3.163 @@ -277,8 +291,13 @@ void serial_set_rx_handler(int handle, s
   3.164  void serial_force_unlock(int handle)
   3.165  {
   3.166      struct serial_port *port = &com[handle & SERHND_IDX];
   3.167 -    if ( handle != -1 )
   3.168 -        port->lock = SPIN_LOCK_UNLOCKED;
   3.169 +
   3.170 +    if ( handle == -1 )
   3.171 +        return;
   3.172 +
   3.173 +    port->rx_lock = SPIN_LOCK_UNLOCKED;
   3.174 +    port->tx_lock = SPIN_LOCK_UNLOCKED;
   3.175 +
   3.176      serial_start_sync(handle);
   3.177  }
   3.178  
   3.179 @@ -290,7 +309,7 @@ void serial_start_sync(int handle)
   3.180      if ( handle == -1 )
   3.181          return;
   3.182      
   3.183 -    spin_lock_irqsave(&port->lock, flags);
   3.184 +    spin_lock_irqsave(&port->tx_lock, flags);
   3.185  
   3.186      if ( port->sync++ == 0 )
   3.187      {
   3.188 @@ -303,7 +322,7 @@ void serial_start_sync(int handle)
   3.189          }
   3.190      }
   3.191  
   3.192 -    spin_unlock_irqrestore(&port->lock, flags);
   3.193 +    spin_unlock_irqrestore(&port->tx_lock, flags);
   3.194  }
   3.195  
   3.196  void serial_end_sync(int handle)
   3.197 @@ -314,11 +333,11 @@ void serial_end_sync(int handle)
   3.198      if ( handle == -1 )
   3.199          return;
   3.200      
   3.201 -    spin_lock_irqsave(&port->lock, flags);
   3.202 +    spin_lock_irqsave(&port->tx_lock, flags);
   3.203  
   3.204      port->sync--;
   3.205  
   3.206 -    spin_unlock_irqrestore(&port->lock, flags);
   3.207 +    spin_unlock_irqrestore(&port->tx_lock, flags);
   3.208  }
   3.209  
   3.210  int serial_tx_space(int handle)

     4.1 --- a/xen/include/xen/serial.h	Thu Mar 23 15:53:52 2006 +0100
     4.2 +++ b/xen/include/xen/serial.h	Thu Mar 23 17:17:08 2006 +0100
     4.3 @@ -42,7 +42,7 @@ struct serial_port {
     4.4      char                rxbuf[SERIAL_RXBUFSZ];
     4.5      unsigned int        rxbufp, rxbufc;
     4.6      /* Serial I/O is concurrency-safe. */
     4.7 -    spinlock_t          lock;
     4.8 +    spinlock_t          rx_lock, tx_lock;
     4.9  };
    4.10  
    4.11  struct uart_driver {