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    Subject[PATCH 11/26] serial: icom: drop low-latency workaround
    Date
    Commit 5faf75d7fed2 ("tty: serial: icom: drop uart_port->lock before
    calling tty_flip_buffer_push()") claimed to address a locking
    issue but only provided a dubious lockdep splat from an unrelated
    driver, which in the end turned out to be due a broken local change
    carried by the author.

    Unfortunately these patches were merged before the issue had been
    analysed properly so the commit messages makes no sense whatsoever.

    The real issue was first seen on RT which at the time effectively always
    set the low_latency flag for all serial drivers by patching
    tty_flip_buffer_push(). This in turn revealed that many drivers did not
    handle the infamous low_latency behaviour which meant that data was
    pushed immediately to the line discipline instead of being deferred to a
    work queue.

    Since commit a9c3f68f3cd8 ("tty: Fix low_latency BUG"),
    tty_flip_buffer_push() always schedules a work item to push data to the
    line discipline and there's no need to keep any low_latency hacks
    around.

    Link: https://lore.kernel.org/linux-serial/cover.1376923198.git.viresh.kumar@linaro.org/
    Signed-off-by: Johan Hovold <johan@kernel.org>
    ---
    drivers/tty/serial/icom.c | 2 --
    1 file changed, 2 deletions(-)

    diff --git a/drivers/tty/serial/icom.c b/drivers/tty/serial/icom.c
    index 94af7a5ea497..9e9abfc4824a 100644
    --- a/drivers/tty/serial/icom.c
    +++ b/drivers/tty/serial/icom.c
    @@ -829,9 +829,7 @@ static void recv_interrupt(u16 port_int_reg, struct icom_port *icom_port)
    }
    icom_port->next_rcv = rcv_buff;

    - spin_unlock(&icom_port->uart_port.lock);
    tty_flip_buffer_push(port);
    - spin_lock(&icom_port->uart_port.lock);
    }

    static void process_interrupt(u16 port_int_reg,
    --
    2.26.3
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