Re: [PATCH v11 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort driver

On Wed, 2022-06-15 at 13:50 +0800, CK Hu wrote:

Hi, Bo-Chen:

On Fri, 2022-06-10 at 18:55 +0800, Bo-Chen Chen wrote:

quoted

From: Markus Schneider-Pargmann <msp@baylibre.com>

This patch adds a embedded displayport driver for the MediaTek
mt8195
SoC.

It supports the MT8195, the embedded DisplayPort units. It offers
DisplayPort 1.4 with up to 4 lanes.

The driver creates a child device for the phy. The child device
will
never exist without the parent being active. As they are sharing a
register range, the parent passes a regmap pointer to the child so
that
both can work with the same register range. The phy driver sets
device
data that is read by the parent to get the phy device that can be
used
to control the phy properties.

This driver is based on an initial version by
Jitao shi [off-list ref]

Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Signed-off-by: Guillaume Ranquet <redacted>
[Bo-Chen: Cleanup the drivers and modify comments from reviewers]
Signed-off-by: Bo-Chen Chen <redacted>
---

[snip]

quoted

+
+static int mtk_dp_train_flow(struct mtk_dp *mtk_dp, u8
target_link_rate,
+			     u8 target_lane_count)
+{
+	u8 lane_adjust[2] = {};
+	bool pass_tps1 = false;
+	bool pass_tps2_3 = false;
+	int train_retries;
+	int status_control;
+	int iteration_count;
+	int ret;
+	u8 prev_lane_adjust;
+
+	drm_dp_dpcd_writeb(&mtk_dp->aux, DP_LINK_BW_SET,
target_link_rate);
+	drm_dp_dpcd_writeb(&mtk_dp->aux, DP_LANE_COUNT_SET,
+			   target_lane_count |
DP_LANE_COUNT_ENHANCED_FRAME_EN);
+
+	if (mtk_dp->train_info.sink_ssc)
+		drm_dp_dpcd_writeb(&mtk_dp->aux, DP_DOWNSPREAD_CTRL,
+				   DP_SPREAD_AMP_0_5);
+
+	train_retries = 0;
+	status_control = 0;
+	iteration_count = 1;
+	prev_lane_adjust = 0xFF;
+
+	mtk_dp_set_lanes(mtk_dp, target_lane_count / 2);
+	ret = mtk_dp_phy_configure(mtk_dp, target_link_rate,
target_lane_count);
+	if (ret)
+		return -EINVAL;
+
+	dev_dbg(mtk_dp->dev,
+		"Link train target_link_rate = 0x%x, target_lane_count
= 0x%x\n",
+		target_link_rate, target_lane_count);
+
+	do {
+		train_retries++;
+		if (!mtk_dp->train_info.cable_plugged_in ||
+		    mtk_dp->train_info.irq_sta.hpd_disconnect) {
+			return -ENODEV;
+		}
+
+		if (mtk_dp->train_state < MTK_DP_TRAIN_STATE_TRAINING)

This checking would never be true, so remove it.

Hello CK,

ok, I will do this.

quoted

+			return -EAGAIN;
+
+		if (!pass_tps1) {
+			ret = mtk_dp_train_tps_1(mtk_dp,
target_lane_count,
+						 &iteration_count,
lane_adjust,
+						 &status_control,
+						 &prev_lane_adjust);
+			if (!ret) {
+				pass_tps1 = true;
+				train_retries = 0;
+			} else if (ret == -EINVAL) {
+				break;
+			}
+		} else {
+			ret = mtk_dp_train_tps_2_3(mtk_dp,
target_link_rate,
+						   target_lane_count,
+						   &iteration_count,
+						   lane_adjust,
&status_control,
+						   &prev_lane_adjust);
+			if (!ret) {
+				pass_tps2_3 = true;
+				break;
+			} else if (ret == -EINVAL) {
+				break;
+			}
+		}
+
+		drm_dp_dpcd_read(&mtk_dp->aux,
DP_ADJUST_REQUEST_LANE0_1,
+				 lane_adjust, sizeof(lane_adjust));
+		mtk_dp_train_update_swing_pre(mtk_dp,
target_lane_count,
+					      lane_adjust);
+	} while (train_retries < MTK_DP_TRAIN_RETRY_LIMIT &&
+		 iteration_count < MTK_DP_TRAIN_MAX_ITERATIONS);

mtk_dp_train_tps_1() & mtk_dp_train_tps_2_3() would only be called
once
and never be called twice, so remove this loop.

Regards,
CK

quoted

+
+	drm_dp_dpcd_writeb(&mtk_dp->aux, DP_TRAINING_PATTERN_SET,
+			   DP_TRAINING_PATTERN_DISABLE);
+	ret = mtk_dp_train_set_pattern(mtk_dp, 0);
+	if (ret)
+		return -EINVAL;
+
+	if (!pass_tps2_3)
+		return -ETIMEDOUT;
+
+	mtk_dp->train_info.link_rate = target_link_rate;
+	mtk_dp->train_info.lane_count = target_lane_count;
+
+	mtk_dp_training_set_scramble(mtk_dp, true);
+
+	drm_dp_dpcd_writeb(&mtk_dp->aux, DP_LANE_COUNT_SET,
+			   target_lane_count |
+				   DP_LANE_COUNT_ENHANCED_FRAME_EN);
+	mtk_dp_set_enhanced_frame_mode(mtk_dp, true);
+
+	return ret;
+}