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

[Tomasz Wroblewski <tomasz.wroblewski@xxxxxxxxxx>]

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);
> >
> > +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.

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