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    Subject[PATCH 4.4 11/28] drm/dp_mst: correct the shifting in DP_REMOTE_I2C_READ
    Date
    From: Wayne Lin <Wayne.Lin@amd.com>

    commit c4e4fccc5d52d881afaac11d3353265ef4eccb8b upstream.

    [Why]
    According to DP spec, it should shift left 4 digits for NO_STOP_BIT
    in REMOTE_I2C_READ message. Not 5 digits.

    In current code, NO_STOP_BIT is always set to zero which means I2C
    master is always generating a I2C stop at the end of each I2C write
    transaction while handling REMOTE_I2C_READ sideband message. This issue
    might have the generated I2C signal not meeting the requirement. Take
    random read in I2C for instance, I2C master should generate a repeat
    start to start to read data after writing the read address. This issue
    will cause the I2C master to generate a stop-start rather than a
    re-start which is not expected in I2C random read.

    [How]
    Correct the shifting value of NO_STOP_BIT for DP_REMOTE_I2C_READ case in
    drm_dp_encode_sideband_req().

    Changes since v1:(https://patchwork.kernel.org/patch/11312667/)
    * Add more descriptions in commit and cc to stable

    Fixes: ad7f8a1f9ced ("drm/helper: add Displayport multi-stream helper (v0.6)")
    Reviewed-by: Harry Wentland <harry.wentland@amd.com>
    Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
    Cc: stable@vger.kernel.org
    Signed-off-by: Lyude Paul <lyude@redhat.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20200103055001.10287-1-Wayne.Lin@amd.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/gpu/drm/drm_dp_mst_topology.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/gpu/drm/drm_dp_mst_topology.c
    +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
    @@ -272,7 +272,7 @@ static void drm_dp_encode_sideband_req(s
    memcpy(&buf[idx], req->u.i2c_read.transactions[i].bytes, req->u.i2c_read.transactions[i].num_bytes);
    idx += req->u.i2c_read.transactions[i].num_bytes;

    - buf[idx] = (req->u.i2c_read.transactions[i].no_stop_bit & 0x1) << 5;
    + buf[idx] = (req->u.i2c_read.transactions[i].no_stop_bit & 0x1) << 4;
    buf[idx] |= (req->u.i2c_read.transactions[i].i2c_transaction_delay & 0xf);
    idx++;
    }

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