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    Subject[PATCH 4.19 291/346] USB: serial: keyspan_pda: fix dropped unthrottle interrupts
    Date
    From: Johan Hovold <johan@kernel.org>

    commit 696c541c8c6cfa05d65aa24ae2b9e720fc01766e upstream.

    Commit c528fcb116e6 ("USB: serial: keyspan_pda: fix receive sanity
    checks") broke write-unthrottle handling by dropping well-formed
    unthrottle-interrupt packets which are precisely two bytes long. This
    could lead to blocked writers not being woken up when buffer space again
    becomes available.

    Instead, stop unconditionally printing the third byte which is
    (presumably) only valid on modem-line changes.

    Fixes: c528fcb116e6 ("USB: serial: keyspan_pda: fix receive sanity checks")
    Cc: stable <stable@vger.kernel.org> # 4.11
    Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Johan Hovold <johan@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/usb/serial/keyspan_pda.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/drivers/usb/serial/keyspan_pda.c
    +++ b/drivers/usb/serial/keyspan_pda.c
    @@ -172,11 +172,11 @@ static void keyspan_pda_rx_interrupt(str
    break;
    case 1:
    /* status interrupt */
    - if (len < 3) {
    + if (len < 2) {
    dev_warn(&port->dev, "short interrupt message received\n");
    break;
    }
    - dev_dbg(&port->dev, "rx int, d1=%d, d2=%d\n", data[1], data[2]);
    + dev_dbg(&port->dev, "rx int, d1=%d\n", data[1]);
    switch (data[1]) {
    case 1: /* modemline change */
    break;

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