From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tomasz Wroblewski <tomasz.wroblewski@citrix.com>
Subject: Re: [PATCH] V2 pci uart - better cope with UART being
 temporarily unavailable
Date: Tue, 27 Aug 2013 15:44:49 +0200
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To: Jan Beulich <JBeulich@suse.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>, keir@xen.org
List-Id: xen-devel@lists.xenproject.org

On 08/27/2013 02:26 PM, Jan Beulich wrote:
>>>> On 27.08.13 at 12:15, Tomasz Wroblewski<tomasz.wroblewski@citrix.com>  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);
>>
>> +out:
> 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
> size.
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.