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    Subject[PATCH 3.16 019/254] drm/i915: Prevent zero length "index" write
    3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Ville Syrjälä <ville.syrjala@linux.intel.com>

    commit 56350fb8978bbf4aafe08f21234e161dd128b417 upstream.

    The hardware always writes one or two bytes in the index portion of
    an indexed transfer. Make sure the message we send as the index
    doesn't have a zero length.

    Cc: Daniel Kurtz <djkurtz@chromium.org>
    Cc: Chris Wilson <chris@chris-wilson.co.uk>
    Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
    Cc: Sean Paul <seanpaul@chromium.org>
    Fixes: 56f9eac05489 ("drm/i915/intel_i2c: use INDEX cycles for i2c read transactions")
    Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20171123194157.25367-3-ville.syrjala@linux.intel.com
    Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
    (cherry picked from commit bb9e0d4bca50f429152e74a459160b41f3d60fb2)
    Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/gpu/drm/i915/intel_i2c.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/drivers/gpu/drm/i915/intel_i2c.c
    +++ b/drivers/gpu/drm/i915/intel_i2c.c
    @@ -449,7 +449,8 @@ gmbus_is_index_read(struct i2c_msg *msgs
    {
    return (i + 1 < num &&
    msgs[i].addr == msgs[i + 1].addr &&
    - !(msgs[i].flags & I2C_M_RD) && msgs[i].len <= 2 &&
    + !(msgs[i].flags & I2C_M_RD) &&
    + (msgs[i].len == 1 || msgs[i].len == 2) &&
    (msgs[i + 1].flags & I2C_M_RD));
    }

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