Re: [Xen-devel] [PATCH] ns16550: delay resume until dom0 ACPI has a chance to run

[Ben Guthro <ben@xxxxxxxxxx>]

On Wed, Jan 16, 2013 at 4:40 PM, Malcolm Crossley
<malcolm.crossley@xxxxxxxxxx> wrote:

> Do these laptops (T430/T530) have built in serial?

They seem to have the hardware for it, but no actual serial connector
out of the machine.
This hardware provides the legacy port that Xen initializes in
xen/arch/x86/setup.c __start_xen()

When the resume happened, it was getting stuck in __ns16550_poll()
because it thought that the
LSR register was 0xFF - and had lots of data to read. It got stuck in
that while loop, and never
exited.


>
> Or is the hang fixed because you were using a serial Express card to debug?
>
> BTW, nearly all PC's have external SUPERIO devices, it just seems we have
> managed to be lucky that most platforms seem to default to using the BIOS to
> enable the serial port after resume instead of the OS.
>
> Malcolm
>
>> Ben
>>
>>
>>
>>> -- Pasi
>>>
>>>
>>>> Signed-Off-By: Ben Guthro <benjamin.guthro@xxxxxxxxxx>
>>>> ---
>>>>    xen/drivers/char/ns16550.c |   56
>>>> +++++++++++++++++++++++++++++++++++++++++++-
>>>>    1 file changed, 55 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
>>>> index d77042e..27555c7 100644
>>>> --- a/xen/drivers/char/ns16550.c
>>>> +++ b/xen/drivers/char/ns16550.c
>>>> @@ -42,6 +42,7 @@ static struct ns16550 {
>>>>        struct irqaction irqaction;
>>>>        /* UART with no IRQ line: periodically-polled I/O. */
>>>>        struct timer timer;
>>>> +    struct timer resume_timer;
>>>>        unsigned int timeout_ms;
>>>>        bool_t intr_works;
>>>>        /* PCI card parameters. */
>>>> @@ -120,6 +121,10 @@ static struct ns16550 {
>>>>    /* Frequency of external clock source. This definition assumes PC
>>>> platform. */
>>>>    #define UART_CLOCK_HZ   1843200
>>>>
>>>> +/* Resume retry settings */
>>>> +#define RESUME_DELAY    MILLISECS(10)
>>>> +#define RESUME_RETRIES  100
>>>> +
>>>>    static char ns_read_reg(struct ns16550 *uart, int reg)
>>>>    {
>>>>        if ( uart->remapped_io_base == NULL )
>>>> @@ -330,7 +335,7 @@ static void ns16550_suspend(struct serial_port
>>>> *port)
>>>>                                      uart->ps_bdf[2], PCI_COMMAND);
>>>>    }
>>>>
>>>> -static void ns16550_resume(struct serial_port *port)
>>>> +static void __ns16550_resume(struct serial_port *port)
>>>>    {
>>>>        struct ns16550 *uart = port->uart;
>>>>
>>>> @@ -346,6 +351,55 @@ static void ns16550_resume(struct serial_port
>>>> *port)
>>>>        ns16550_setup_postirq(port->uart);
>>>>    }
>>>>
>>>> +static int ns16550_ioport_invalid(struct ns16550 *uart)
>>>> +{
>>>> +    return ((((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));
>>>> +}
>>>> +
>>>> +static int delayed_resume_tries;
>>>> +static void ns16550_delayed_resume(void *data)
>>>> +{
>>>> +    struct serial_port *port = data;
>>>> +    struct ns16550 *uart = port->uart;
>>>> +
>>>> +    if (ns16550_ioport_invalid(port->uart) && delayed_resume_tries--) {
>>>> +       set_timer(&uart->resume_timer, NOW() + RESUME_DELAY);
>>>> +       return;
>>>> +    }
>>>> +
>>>> +    __ns16550_resume(port);
>>>> +}
>>>> +
>>>> +static void ns16550_resume(struct serial_port *port)
>>>> +{
>>>> +    struct ns16550 *uart = port->uart;
>>>> +
>>>> +    /*
>>>> +     * Check for ioport access, before fully resuming operation.
>>>> +     * On some systems, there is a SuperIO card that provides
>>>> +     * this legacy ioport on the LPC bus.
>>>> +     *
>>>> +     * We need to wait for dom0's ACPI processing to run the proper
>>>> +     * AML to re-initialize the chip, before we can use the card again.
>>>> +     *
>>>> +     * This may cause a small amount of garbage to be written
>>>> +     * to the serial log while we wait patiently for that AML to
>>>> +     * be executed.
>>>> +     */
>>>> +    if (ns16550_ioport_invalid(uart)) {
>>>> +       delayed_resume_tries = RESUME_RETRIES;
>>>> +       init_timer(&uart->resume_timer, ns16550_delayed_resume, port,
>>>> 0);
>>>> +       set_timer(&uart->resume_timer, NOW() + RESUME_DELAY);
>>>> +       return;
>>>> +    }
>>>> +
>>>> +    __ns16550_resume(port);
>>>> +}
>>>> +
>>>>    #ifdef CONFIG_X86
>>>>    static void __init ns16550_endboot(struct serial_port *port)
>>>>    {
>>>> --
>>>> 1.7.9.5
>>>>
>>>>
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