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    Subject[PATCH] i2c-algo-bit: Fix spurious SCL timeouts under heavy load
    Date
    When the system is under heavy load, there can be a significant delay
    between the getscl() and time_after() calls inside sclhi(). That delay
    may cause the time_after() check to trigger after SCL has gone high,
    causing sclhi() to return -ETIMEDOUT.

    To fix the problem, double check that SCL is still low after the
    timeout has been reached, before deciding to return -ETIMEDOUT.

    Signed-off-by: Ville Syrjälä <syrjala@sci.fi>
    ---
    I can easily reproduce these spurious timeouts on my HP-compaq nc6000
    laptop with the radeon kms driver. It's enough to have a -j2 kernel
    build running, and simultaneosly issue xrandr commands in a
    terminal. Calling xrandr will cause the driver to re-read the EDID
    from the display. A significant number of the EDID reads will fail.
    With this fix I have yet to see any failed EDID reads.

    drivers/i2c/algos/i2c-algo-bit.c | 4 +++-
    1 files changed, 3 insertions(+), 1 deletions(-)

    diff --git a/drivers/i2c/algos/i2c-algo-bit.c b/drivers/i2c/algos/i2c-algo-bit.c
    index 525c734..d25112e 100644
    --- a/drivers/i2c/algos/i2c-algo-bit.c
    +++ b/drivers/i2c/algos/i2c-algo-bit.c
    @@ -104,9 +104,11 @@ static int sclhi(struct i2c_algo_bit_data *adap)
    * are processing data internally.
    */
    if (time_after(jiffies, start + adap->timeout))
    - return -ETIMEDOUT;
    + break;
    cond_resched();
    }
    + if (!getscl(adap))
    + return -ETIMEDOUT;
    #ifdef DEBUG
    if (jiffies != start && i2c_debug >= 3)
    pr_debug("i2c-algo-bit: needed %ld jiffies for SCL to go "
    --
    1.7.3.4
    --
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