4.19-stable review patch. If anyone has any objections, please let me know.
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[ Upstream commit c978ae9bde582e82a04c63a4071701691dd8b35c ]
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.s... Reviewed-by: Dhinakaran Pandiyan dhinakaran.pandiyan@intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/drm_dp_mst_topology.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index d708472d93c4..65f58e23e03d 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -3278,6 +3278,7 @@ 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;