CHR_IOCTL_SERIAL_{GET,SET}_TIOCM

CHR_IOCTL_SERIAL_{GET,SET}_TIOCM

Remaining fragments of xen-unstable c/s
16537:bf21e00155b7dd76653c5340099ecedac7a7de08

    [QEMU-DM] Modem control line & msl/mcr register support.

    This patch enables handling of the modem/flow control lines of a
    serial port when the backend for the virtual port is a physical serial
    port. During initialization, it tries to load the msr with the
    detected status from the real port (this is consistent with physical
    uart, which starts with its msr values set according to the status of
    the modem status lines). If the ioctl returns -ENOTSUP, then the code
    assumes the backend is not a real serial port and will disable any
    further attempts to manipulate or read the physical port's line
    status.

    It's tries to be as "correct" as possible in its msr/msl handling,
    with the exception of modem line status change interrupts. A real
    16550 uart apparently have a delay time of 250ns between when a modem
    status line changes and the IRQ line goes high. In this patch, an
    "idle" port is polled for line status changes only if the guest has
    enabled UART_IER_MSI is enabled, and only polled every 10 ms.

    Signed-off-by: Trolle Selander <trolle.selander@gmail.com>