Hi, Rex:

On Mon, 2022-05-23 at 12:47 +0200, Guillaume Ranquet wrote:

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

This patch adds a 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
Jason-JH.Lin [off-list ref].

Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Signed-off-by: Guillaume Ranquet <redacted>
---

[snip]

+
+static int mtk_dp_train_start(struct mtk_dp *mtk_dp)
+{
+	int ret = 0;
+	u8 lane_count;
+	u8 link_rate;
+	u8 train_limit;
+	u8 max_link_rate;
+	u8 plug_wait;
+
+	for (plug_wait = 7; !mtk_dp_plug_state(mtk_dp) && plug_wait >
0;
+	     --plug_wait)
+		/* Avoid short pulses on the HPD isr */
+		usleep_range(1000, 5000);
+	if (plug_wait == 0) {
+		mtk_dp->train_state = MTK_DP_TRAIN_STATE_DPIDLE;

After return, mtk_dp->train_state would be set to
MTK_DP_TRAIN_STATE_DPIDLE, so drop this.

+		return -ENODEV;
+	}
+
+	link_rate = mtk_dp->rx_cap[1];
+	lane_count = mtk_dp->rx_cap[2] & 0x1F;
+
+	mtk_dp->train_info.link_rate = min(mtk_dp->max_linkrate,
link_rate);
+	mtk_dp->train_info.lane_count = min(mtk_dp->max_lanes,
lane_count);
+	link_rate = mtk_dp->train_info.link_rate;
+	lane_count = mtk_dp->train_info.lane_count;
+
+	switch (link_rate) {
+	case MTK_DP_LINKRATE_RBR:
+	case MTK_DP_LINKRATE_HBR:
+	case MTK_DP_LINKRATE_HBR2:
+	case MTK_DP_LINKRATE_HBR25:
+	case MTK_DP_LINKRATE_HBR3:
+		break;
+	default:
+		mtk_dp->train_info.link_rate = MTK_DP_LINKRATE_HBR3;
+		break;
+	};
+
+	max_link_rate = link_rate;
+	for (train_limit = 6; train_limit > 0; train_limit--) {
+		mtk_dp->train_info.cr_done = false;
+		mtk_dp->train_info.eq_done = false;
+
+		mtk_dp_train_change_mode(mtk_dp);
+		ret = mtk_dp_train_flow(mtk_dp, link_rate, lane_count);
+		if (ret)
+			return ret;
+
+		if (!mtk_dp->train_info.cr_done) {
+			switch (link_rate) {
+			case MTK_DP_LINKRATE_RBR:
+				lane_count = lane_count / 2;
+				link_rate = max_link_rate;
+				if (lane_count == 0) {
+					mtk_dp->train_state =
+						MTK_DP_TRAIN_STATE_DPID
LE;

After return, mtk_dp->train_state would be set to
MTK_DP_TRAIN_STATE_DPIDLE, so drop this.

Regards,
CK

+					return -EIO;
+				}
+				break;
+			case MTK_DP_LINKRATE_HBR:
+				link_rate = MTK_DP_LINKRATE_RBR;
+				break;
+			case MTK_DP_LINKRATE_HBR2:
+				link_rate = MTK_DP_LINKRATE_HBR;
+				break;
+			case MTK_DP_LINKRATE_HBR3:
+				link_rate = MTK_DP_LINKRATE_HBR2;
+				break;
+			default:
+				return -EINVAL;
+			};
+		} else if (!mtk_dp->train_info.eq_done) {
+			if (lane_count == 0)
+				return -EIO;
+
+			lane_count /= 2;
+		} else {
+			break;
+		}
+	}
+
+	if (train_limit == 0)
+		return -ETIMEDOUT;
+
+	return 0;
+}
+