drm/dp/mst: Configure no_stop_bit correctly for remote i2c xfers

We aren't supposed to force a stop+start between every i2c msg
when performing multi message transfers. This should eg. cause
the DDC segment address to be reset back to 0 between writing
the segment address and reading the actual EDID extension block.

To quote the E-DDC spec:
"... this standard requires that the segment pointer be
 reset to 00h when a NO ACK or a STOP condition is received."

Since we're going to touch this might as well consult the
I2C_M_STOP flag to determine whether we want to force the stop
or not.

Cc: Brian Vincent <brainn@gmail.com>
References: https://bugs.freedesktop.org/show_bug.cgi?id=108081
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180928180403.22499-1-ville.syrjala@linux.intel.com
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index a9b684f..229ad60 100644 (file)
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3287,6 +3287,7 @@ static int drm_dp_mst_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs
                msg.u.i2c_read.transactions[i].i2c_dev_id = msgs[i].addr;
                msg.u.i2c_read.transactions[i].num_bytes = msgs[i].len;
                msg.u.i2c_read.transactions[i].bytes = msgs[i].buf;
+               msg.u.i2c_read.transactions[i].no_stop_bit = !(msgs[i].flags & I2C_M_STOP);
        }
        msg.u.i2c_read.read_i2c_device_id = msgs[num - 1].addr;
        msg.u.i2c_read.num_bytes_read = msgs[num - 1].len;