Hi, Bo-Chen:

On Tue, 2022-07-12 at 19:12 +0800, Bo-Chen Chen wrote:

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>
Signed-off-by: Bo-Chen Chen <redacted>
---

[snip]

+static void mtk_dp_hpd_sink_event(struct mtk_dp *mtk_dp)
+{
+	ssize_t ret;
+	u8 sink_count;
+	u8 link_status[DP_LINK_STATUS_SIZE] = {};
+	u32 sink_count_reg = DP_SINK_COUNT_ESI;
+	u32 link_status_reg = DP_LANE0_1_STATUS;
+
+	ret = drm_dp_dpcd_readb(&mtk_dp->aux, sink_count_reg,
&sink_count);

According to your last reply, if drm_dp_dpcd_readb() fail, we could
skip below statement. So this just for error checking? If so, the next
drm_dp_dpcd_read() would also do the error checking, so the checking
here is redundant.

Regards,
CK

+	if (ret < 1) {
+		drm_err(mtk_dp->drm_dev, "Read sink count failed\n");
+		return;
+	}
+
+	drm_dbg(mtk_dp->drm_dev,
+		"read sink count from dpcd: %d\n", sink_count);
+
+	ret = drm_dp_dpcd_read(&mtk_dp->aux, link_status_reg,
link_status,
+			       sizeof(link_status));
+	if (!ret) {
+		drm_err(mtk_dp->drm_dev, "Read link status failed\n");
+		return;
+	}
+
+	if (!drm_dp_channel_eq_ok(link_status, mtk_dp-

quoted

train_info.lane_count)) {

+		drm_err(mtk_dp->drm_dev, "Channel EQ failed\n");
+		return;
+	}
+
+	if (link_status[1] & DP_REMOTE_CONTROL_COMMAND_PENDING)
+		drm_dp_dpcd_writeb(&mtk_dp->aux,
DP_DEVICE_SERVICE_IRQ_VECTOR,
+				   DP_REMOTE_CONTROL_COMMAND_PENDING);
+}
+