drm/bridge: analogix_dp: Fix incorrect usage of enhanced mode

Enhanced mode is required by the eDP 1.2 specification, and not doing it
early could result in a period of time where we have a link transmitting
idle packets without it. Since there is no reason to disable it, we just
enable it at the beginning of link training and then keep it on all the
time.

Cc: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Nzain wang <wzz@rock-chips.com>
Signed-off-by: NSean Paul <seanpaul@chromium.org>
Signed-off-by: NThierry Escande <thierry.escande@collabora.com>
Reviewed-by: NAndrzej Hajda <a.hajda@samsung.com>
Signed-off-by: NEnric Balletbo i Serra <enric.balletbo@collabora.com>
Tested-by: NMarek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: NArchit Taneja <architt@codeaurora.org>
Signed-off-by: NAndrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180423105003.9004-10-enric.balletbo@collabora.com

drivers/gpu/drm/bridge/analogix/analogix_dp_core.c

@@ -281,6 +281,8 @@ static int analogix_dp_link_start(struct analogix_dp_device *dp)
 	retval = drm_dp_dpcd_write(&dp->aux, DP_LINK_BW_SET, buf, 2);
 	if (retval < 0)
 		return retval;
+	/* set enhanced mode if available */
+	analogix_dp_set_enhanced_mode(dp);
 
 	/* Set TX pre-emphasis to minimum */
 	for (lane = 0; lane < lane_count; lane++)
@@ -593,8 +595,6 @@ static int analogix_dp_process_equalizer_training(struct analogix_dp_device *dp)
 		dev_dbg(dp->dev, "fast link training %s\n",
 			dp->fast_train_enable ? "supported" : "unsupported");
 
-		/* set enhanced mode if available */
-		analogix_dp_set_enhanced_mode(dp);
 		dp->link_train.lt_state = FINISHED;
 
 		return 0;
@@ -940,8 +940,6 @@ static int analogix_dp_commit(struct analogix_dp_device *dp)
 	}
 
 	analogix_dp_enable_scramble(dp, 1);
-	analogix_dp_enable_rx_to_enhanced_mode(dp, 1);
-	analogix_dp_enable_enhanced_mode(dp, 1);
 
 	analogix_dp_init_video(dp);
 	ret = analogix_dp_config_video(dp);