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    Subject[PATCH 3.12 064/107] [media] dib8000: make 32 bits read atomic
    Date
    3.12-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Mauro Carvalho Chehab <m.chehab@samsung.com>

    commit 5ac64ba12aca3bef18e61c866583155a3bbf81c4 upstream.

    As the dvb-frontend kthread can be called anytime, it can race
    with some get status ioctl. So, it seems better to avoid one to
    race with the other while reading a 32 bits register.
    I can't see any other reason for having a mutex there at I2C, except
    to provide such kind of protection, as the I2C core already has a
    mutex to protect I2C transfers.

    Note: instead of this approach, it could eventually remove the dib8000
    specific mutex for it, and either group the 4 ops into one xfer or
    to manually control the I2C mutex. The main advantage of the current
    approach is that the changes are smaller and more puntual.

    Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
    Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
    Acked-by: Patrick Boettcher <pboettcher@kernellabs.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/media/dvb-frontends/dib8000.c | 33 +++++++++++++++++++++++++--------
    1 file changed, 25 insertions(+), 8 deletions(-)

    --- a/drivers/media/dvb-frontends/dib8000.c
    +++ b/drivers/media/dvb-frontends/dib8000.c
    @@ -157,15 +157,10 @@ static u16 dib8000_i2c_read16(struct i2c
    return ret;
    }

    -static u16 dib8000_read_word(struct dib8000_state *state, u16 reg)
    +static u16 __dib8000_read_word(struct dib8000_state *state, u16 reg)
    {
    u16 ret;

    - if (mutex_lock_interruptible(&state->i2c_buffer_lock) < 0) {
    - dprintk("could not acquire lock");
    - return 0;
    - }
    -
    state->i2c_write_buffer[0] = reg >> 8;
    state->i2c_write_buffer[1] = reg & 0xff;

    @@ -183,6 +178,21 @@ static u16 dib8000_read_word(struct dib8
    dprintk("i2c read error on %d", reg);

    ret = (state->i2c_read_buffer[0] << 8) | state->i2c_read_buffer[1];
    +
    + return ret;
    +}
    +
    +static u16 dib8000_read_word(struct dib8000_state *state, u16 reg)
    +{
    + u16 ret;
    +
    + if (mutex_lock_interruptible(&state->i2c_buffer_lock) < 0) {
    + dprintk("could not acquire lock");
    + return 0;
    + }
    +
    + ret = __dib8000_read_word(state, reg);
    +
    mutex_unlock(&state->i2c_buffer_lock);

    return ret;
    @@ -192,8 +202,15 @@ static u32 dib8000_read32(struct dib8000
    {
    u16 rw[2];

    - rw[0] = dib8000_read_word(state, reg + 0);
    - rw[1] = dib8000_read_word(state, reg + 1);
    + if (mutex_lock_interruptible(&state->i2c_buffer_lock) < 0) {
    + dprintk("could not acquire lock");
    + return 0;
    + }
    +
    + rw[0] = __dib8000_read_word(state, reg + 0);
    + rw[1] = __dib8000_read_word(state, reg + 1);
    +
    + mutex_unlock(&state->i2c_buffer_lock);

    return ((rw[0] << 16) | (rw[1]));
    }



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