[PATCH] PCI uart: fix boot hang, and second S3 resume inactive timer list corruption

[Tomasz Wroblewski <tomasz.wroblewski@citrix.com>]

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Couple PCI uart resume/boot fixes
    
- fix occasional xen boot hang whilst using PCI uart. Dom0 kernel disables ioport responses
  during PCI system initialisation, causing xen hang if __ns16550_poll() routine happens to
  be scheduled during that time. Detect and exit. Amended ns16550_ioport_invalid function
  to only check IER register, which contains three reservered (always 0) bits, therefore
  it's sufficient for this test.
    
- fix second s3 resume failures due to inactive timer list corruption. init_timer cannot be safely
  called multiple times on same timer since it does memset(0) on the structure, erasing the
  auxiliary member used by linked list code, breaking the inactive timer list in common/timer.c.
  Moved resume_timer initialisation to ns16550_init_postirq, so it's only done once.
    
Signed-off-by: Tomasz Wroblewski <tomasz.wroblewski@citrix.com>

diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
index 6082c85..3ef096e 100644
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -59,6 +59,8 @@ static struct ns16550 {
     u8 bar_idx;
 } ns16550_com[2] = { { 0 } };
 
+static void ns16550_delayed_resume(void *data);
+
 static char ns_read_reg(struct ns16550 *uart, int reg)
 {
     if ( uart->remapped_io_base == NULL )
@@ -73,6 +75,11 @@ static void ns_write_reg(struct ns16550 *uart, int reg, char c)
     writeb(c, uart->remapped_io_base + reg);
 }
 
+static int ns16550_ioport_invalid(struct ns16550 *uart)
+{
+    return (((unsigned char)ns_read_reg(uart, UART_IER)) == 0xff);
+}
+
 static void ns16550_interrupt(
     int irq, void *dev_id, struct cpu_user_regs *regs)
 {
@@ -103,11 +110,16 @@ static void __ns16550_poll(struct cpu_user_regs *regs)
         return; /* Interrupts work - no more polling */
 
     while ( ns_read_reg(uart, UART_LSR) & UART_LSR_DR )
+    {
         serial_rx_interrupt(port, regs);
+        if ( ns16550_ioport_invalid(uart) )
+            goto out;
+    }
 
     if ( ns_read_reg(uart, UART_LSR) & UART_LSR_THRE )
         serial_tx_interrupt(port, regs);
 
+out:
     set_timer(&uart->timer, NOW() + MILLISECS(uart->timeout_ms));
 }
 
@@ -256,6 +268,7 @@ static void __init ns16550_init_postirq(struct serial_port *port)
     serial_async_transmit(port);
 
     init_timer(&uart->timer, ns16550_poll, port, 0);
+    init_timer(&uart->resume_timer, ns16550_delayed_resume, port, 0);
 
     /* Calculate time to fill RX FIFO and/or empty TX FIFO for polling. */
     bits = uart->data_bits + uart->stop_bits + !!uart->parity;
@@ -305,15 +318,6 @@ static void _ns16550_resume(struct serial_port *port)
     ns16550_setup_postirq(port->uart);
 }
 
-static int ns16550_ioport_invalid(struct ns16550 *uart)
-{
-    return ((((unsigned char)ns_read_reg(uart, UART_LSR)) == 0xff) &&
-            (((unsigned char)ns_read_reg(uart, UART_MCR)) == 0xff) &&
-            (((unsigned char)ns_read_reg(uart, UART_IER)) == 0xff) &&
-            (((unsigned char)ns_read_reg(uart, UART_IIR)) == 0xff) &&
-            (((unsigned char)ns_read_reg(uart, UART_LCR)) == 0xff));
-}
-
 static int delayed_resume_tries;
 static void ns16550_delayed_resume(void *data)
 {
@@ -346,7 +350,6 @@ static void ns16550_resume(struct serial_port *port)
     if ( ns16550_ioport_invalid(uart) )
     {
         delayed_resume_tries = RESUME_RETRIES;
-        init_timer(&uart->resume_timer, ns16550_delayed_resume, port, 0);
         set_timer(&uart->resume_timer, NOW() + RESUME_DELAY);
     }
     else

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