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    Subject[PATCH 06/18] Blackfin Serial Driver: explain why we cannot cpu_relax() in early serial code
    Date
    From: Mike Frysinger <vapier.adi@gmail.com>

    Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
    Signed-off-by: Bryan Wu <cooloney@kernel.org>
    ---
    drivers/serial/bfin_5xx.c | 4 ++++
    1 files changed, 4 insertions(+), 0 deletions(-)

    diff --git a/drivers/serial/bfin_5xx.c b/drivers/serial/bfin_5xx.c
    index 5a163f6..de8709d 100644
    --- a/drivers/serial/bfin_5xx.c
    +++ b/drivers/serial/bfin_5xx.c
    @@ -1190,6 +1190,10 @@ static __init void early_serial_putc(struct uart_port *port, int ch)
    unsigned timeout = 0xffff;
    struct bfin_serial_port *uart = (struct bfin_serial_port *)port;

    + /* We cannot cpu_relax() here as doing so on the BF561 relies
    + * on the per-cpu region being setup, and since this is early
    + * serial code, it may not yet be usable ...
    + */
    while ((!(UART_GET_LSR(uart) & THRE)) && --timeout)
    barrier();

    --
    1.5.6.3

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