Re: S3 resume issues

[Malcolm Crossley <malcolm.crossley@citrix.com>]

On 15/01/13 18:10, Ben Guthro wrote:
> On Tue, Jan 15, 2013 at 7:55 AM, Ben Guthro <ben@guthro.net> wrote:
>> I'll continue down the rcu_check_callbacks() path, I guess.
> I believe I've found the culprit of the issue, but am unsure of what
> the proper solution is.
>
> It looks like after resume, on these newer machines, the ns16550
> registers contain all FF's - and so, the timer code was getting stuck
> in
> __ns16550_poll in the following stack:
>
> __ns16550_poll()
> execute_timer()
> timer_softirq_action()
> __do_softirq()
> process_pending_softirqs()
> rcu_barrier_action()
> rcu_barrier()
> enter_state()
>
> The while loop in this function was spinning, calling
> serial_rx_interrupt() over, and over again, since the LSR register was
> 0xFF
>
> A workaround seems to be to check some of the named registers at
> resume time, and bail out if they contain 0xFF's:
>
> diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
> index d77042e..b370581 100644
> --- a/xen/drivers/char/ns16550.c
> +++ b/xen/drivers/char/ns16550.c
> @@ -342,6 +342,15 @@ static void ns16550_resume(struct serial_port *port)
>                           PCI_COMMAND, uart->cr);
>       }
>
> +    if ( (((unsigned char)ns_read_reg(uart, LSR)) == 0xff) &&
> +         (((unsigned char)ns_read_reg(uart, MCR)) == 0xff) &&
> +         (((unsigned char)ns_read_reg(uart, IER)) == 0xff) &&
> +         (((unsigned char)ns_read_reg(uart, IIR)) == 0xff) &&
> +         (((unsigned char)ns_read_reg(uart, LCR)) == 0xff) ) {
> +        printk(KERN_ERR "ns16550 resume has bad register data!\n");
> +       return;
> +    }
> +
>       ns16550_setup_preirq(port->uart);
>       ns16550_setup_postirq(port->uart);
>   }
>
>
> This, of course means that you don't get any serial data after resume,
> which is not ideal.
>
>
> I'm going to try to figure out if there is any chipset (Panther Point)
> specific initialization that should be getting done.
> If you (or anyone else) has any other thoughts on this serial
> initialization, please let me know.
>
>
> Ben
You get 0xFF when there is nothing responding to the ioport. If the 
16550 is on a PCI card then it could be the PCI connection has not been 
setup again after the resume and you can't get to that ioport range.

Malcolm