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Re: [Xen-devel] [PATCH] V2 pci uart - better cope with UART being temporarily unavailable

On 08/27/2013 02:26 PM, Jan Beulich wrote:
On 27.08.13 at 12:15, Tomasz Wroblewski<tomasz.wroblewski@xxxxxxxxxx>  wrote:
@@ -102,12 +107,17 @@ static void __ns16550_poll(struct cpu_user_regs *regs)
      if ( uart->intr_works )
          return; /* Interrupts work - no more polling */

-    while ( ns_read_reg(uart, UART_LSR)&  UART_LSR_DR )
-        serial_rx_interrupt(port, regs);
+     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);

So serial_rx_interrupt() gets run once in that case, but
serial_tx_interrupt() not at all? That not only inconsistent, I also
can't see why anything would need to be done here at all in this
case. Plus doing the check before the loop would shrink patch
So I presume it is impossible for dom0 code to run on another cpu whilst xen is executing the poll routine, I was not sure at all about this? Would like to avoid the possibility of dom0 disabling device whilst this loop is running.

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