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 15:36:39 +0200
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>> --- a/xen/drivers/char/serial.c
>> +++ b/xen/drivers/char/serial.c
>> @@ -111,15 +111,18 @@ static void __serial_putc(struct serial_port *port, char c)
>>               if ( port->tx_log_everything )
>>               {
>>                   /* Buffer is full: we spin waiting for space to appear. */
>> -                unsigned int n;
>> +                int n;
>>
>>                   while ( (n = port->driver->tx_ready(port)) == 0 )
>>                       cpu_relax();
>> -                while ( n-- )
>> -                    port->driver->putc(
>> -                        port,
>> -                        port->txbuf[mask_serial_txbuf_idx(port->txbufc++)]);
>> -                port->txbuf[mask_serial_txbuf_idx(port->txbufp++)] = c;
>> +                if (n>  0)
>> +                {
>> +                    while ( n-- )
> "while ( n-->  0 )" can achieve the same without the extra if()
> and with just a one line change.
Thanks for review - agree with most comments except this one, we need to 
avoid executing "port->txbuf[mask_serial_txbuf_idx(port->txbufp++)] = c" 
if port is offline, since in this case the while loop will not consume 
pull any character out of the buffer, and it will stay full, and we 
should just drop the char. The "if" I added pulled the buffer insert 
into its body.