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    Subject[PATCH 1/2] drm/i915/intel_i2c: handle zero-length reads
    Date
    A common method of probing an i2c bus is trying to do a zero-length read.
    Handle this case by checking the length first waiting for data to be read.

    This is actually important, since attempting a zero-length read 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 | 4 ++--
    1 files changed, 2 insertions(+), 2 deletions(-)

    diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
    index cab879f..e249160 100644
    --- a/drivers/gpu/drm/i915/intel_i2c.c
    +++ b/drivers/gpu/drm/i915/intel_i2c.c
    @@ -217,7 +217,7 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
    (len << GMBUS_BYTE_COUNT_SHIFT) |
    (msg->addr << GMBUS_SLAVE_ADDR_SHIFT) |
    GMBUS_SLAVE_READ | GMBUS_SW_RDY);
    - do {
    + while (len) {
    int ret;
    u32 val, loop = 0;
    u32 gmbus2;
    @@ -235,7 +235,7 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
    *buf++ = val & 0xff;
    val >>= 8;
    } while (--len && ++loop < 4);
    - } while (len);
    + }

    return 0;
    }
    --
    1.7.7.3


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