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    Subject[PATCH 3.12 66/86] tty: nozomi: avoid a harmless gcc warning
    Date
    From: Arnd Bergmann <arnd@arndb.de>

    3.12-stable review patch. If anyone has any objections, please let me know.

    ===============

    commit a4f642a8a3c2838ad09fe8313d45db46600e1478 upstream.

    The nozomi wireless data driver has its own helper function to
    transfer data from a FIFO, doing an extra byte swap on big-endian
    architectures, presumably to bring the data back into byte-serial
    order after readw() or readl() perform their implicit byteswap.

    This helper function is used in the receive_data() function to
    first read the length into a 32-bit variable, which causes
    a compile-time warning:

    drivers/tty/nozomi.c: In function 'receive_data':
    drivers/tty/nozomi.c:857:9: warning: 'size' may be used uninitialized in this function [-Wmaybe-uninitialized]

    The problem is that gcc is unsure whether the data was actually
    read or not. We know that it is at this point, so we can replace
    it with a single readl() to shut up that warning.

    I am leaving the byteswap in there, to preserve the existing
    behavior, even though this seems fishy: Reading the length of
    the data into a cpu-endian variable should normally not use
    a second byteswap on big-endian systems, unless the hardware
    is aware of the CPU endianess.

    There appears to be a lot more confusion about endianess in this
    driver, so it probably has not worked on big-endian systems in
    a long time, if ever, and I have no way to test it. It's well
    possible that this driver has not been used by anyone in a while,
    the last patch that looks like it was tested on the hardware is
    from 2008.

    Signed-off-by: Arnd Bergmann <arnd@arndb.de>
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    ---
    drivers/tty/nozomi.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/drivers/tty/nozomi.c b/drivers/tty/nozomi.c
    index d6080c3831ef..ce2e5d508fe7 100644
    --- a/drivers/tty/nozomi.c
    +++ b/drivers/tty/nozomi.c
    @@ -823,7 +823,7 @@ static int receive_data(enum port_type index, struct nozomi *dc)
    struct tty_struct *tty = tty_port_tty_get(&port->port);
    int i, ret;

    - read_mem32((u32 *) &size, addr, 4);
    + size = __le32_to_cpu(readl(addr));
    /* DBG1( "%d bytes port: %d", size, index); */

    if (tty && test_bit(TTY_THROTTLED, &tty->flags)) {
    --
    2.12.2
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