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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>
This commit is contained in:
Ville Syrjälä 2018-09-28 21:03:59 +03:00
parent 32658d2c80
commit c978ae9bde
1 changed files with 1 additions and 0 deletions
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1
drivers/gpu/drm/drm_dp_mst_topology.c
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@ -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;