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    Subject[PATCH 1/8 v7] drm/i915/intel_i2c: handle zero-length writes
    Date
    A common method of probing an i2c bus is trying to do a zero-length write.
    Handle this case by checking the length first before decrementing it.

    This is actually important, since attempting a zero-length write is one
    of the ways that i2cdetect and i2c_new_probed_device detect whether
    there is device present on the bus with a given address.

    Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
    ---
    drivers/gpu/drm/i915/intel_i2c.c | 7 ++++---
    1 files changed, 4 insertions(+), 3 deletions(-)

    diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
    index c12db72..99a04f8 100644
    --- a/drivers/gpu/drm/i915/intel_i2c.c
    +++ b/drivers/gpu/drm/i915/intel_i2c.c
    @@ -248,9 +248,10 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
    u32 val, loop;

    val = loop = 0;
    - do {
    - val |= *buf++ << (8 * loop);
    - } while (--len && ++loop < 4);
    + while (len && loop < 4) {
    + val |= *buf++ << (8 * loop++);
    + len -= 1;
    + }

    I915_WRITE(GMBUS3 + reg_offset, val);
    I915_WRITE(GMBUS1 + reg_offset,
    --
    1.7.7.3


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