drm/amd/display: Add MST Preferred Link Setting Entry

When using debugfs to change MST link settings, we need to wait until
the next stream update to apply the preferred link setting. So, trigger
a hotplug event right after the preferred link setting is applied.
Reviewed-by: Wayne Lin <wayne.lin@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Fangzhi Zuo <jerry.zuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c

@@ -336,6 +336,153 @@ static ssize_t dp_link_settings_write(struct file *f, const char __user *buf,
 	return size;
 }
 
+static bool dp_mst_is_end_device(struct amdgpu_dm_connector *aconnector)
+{
+	bool is_end_device = false;
+	struct drm_dp_mst_topology_mgr *mgr = NULL;
+	struct drm_dp_mst_port *port = NULL;
+
+	if (aconnector->mst_root && aconnector->mst_root->mst_mgr.mst_state) {
+		mgr = &aconnector->mst_root->mst_mgr;
+		port = aconnector->mst_output_port;
+
+		drm_modeset_lock(&mgr->base.lock, NULL);
+		if (port->pdt == DP_PEER_DEVICE_SST_SINK ||
+			port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV)
+			is_end_device = true;
+		drm_modeset_unlock(&mgr->base.lock);
+	}
+
+	return is_end_device;
+}
+
+/* Change MST link setting
+ *
+ * valid lane count value: 1, 2, 4
+ * valid link rate value:
+ * 06h = 1.62Gbps per lane
+ * 0Ah = 2.7Gbps per lane
+ * 0Ch = 3.24Gbps per lane
+ * 14h = 5.4Gbps per lane
+ * 1Eh = 8.1Gbps per lane
+ * 3E8h = 10.0Gbps per lane
+ * 546h = 13.5Gbps per lane
+ * 7D0h = 20.0Gbps per lane
+ *
+ * debugfs is located at /sys/kernel/debug/dri/0/DP-x/mst_link_settings
+ *
+ * for example, to force to  2 lane, 10.0GHz,
+ * echo 2 0x3e8 > /sys/kernel/debug/dri/0/DP-x/mst_link_settings
+ *
+ * Valid input will trigger hotplug event to get new link setting applied
+ * Invalid input will trigger training setting reset
+ *
+ * The usage can be referred to link_settings entry
+ *
+ */
+static ssize_t dp_mst_link_setting(struct file *f, const char __user *buf,
+				 size_t size, loff_t *pos)
+{
+	struct amdgpu_dm_connector *aconnector = file_inode(f)->i_private;
+	struct dc_link *link = aconnector->dc_link;
+	struct amdgpu_device *adev = drm_to_adev(aconnector->base.dev);
+	struct dc *dc = (struct dc *)link->dc;
+	struct dc_link_settings prefer_link_settings;
+	char *wr_buf = NULL;
+	const uint32_t wr_buf_size = 40;
+	/* 0: lane_count; 1: link_rate */
+	int max_param_num = 2;
+	uint8_t param_nums = 0;
+	long param[2];
+	bool valid_input = true;
+
+	if (!dp_mst_is_end_device(aconnector))
+		return -EINVAL;
+
+	if (size == 0)
+		return -EINVAL;
+
+	wr_buf = kcalloc(wr_buf_size, sizeof(char), GFP_KERNEL);
+	if (!wr_buf)
+		return -ENOSPC;
+
+	if (parse_write_buffer_into_params(wr_buf, wr_buf_size,
+					   (long *)param, buf,
+					   max_param_num,
+					   &param_nums)) {
+		kfree(wr_buf);
+		return -EINVAL;
+	}
+
+	if (param_nums <= 0) {
+		kfree(wr_buf);
+		DRM_DEBUG_DRIVER("user data not be read\n");
+		return -EINVAL;
+	}
+
+	switch (param[0]) {
+	case LANE_COUNT_ONE:
+	case LANE_COUNT_TWO:
+	case LANE_COUNT_FOUR:
+		break;
+	default:
+		valid_input = false;
+		break;
+	}
+
+	switch (param[1]) {
+	case LINK_RATE_LOW:
+	case LINK_RATE_HIGH:
+	case LINK_RATE_RBR2:
+	case LINK_RATE_HIGH2:
+	case LINK_RATE_HIGH3:
+	case LINK_RATE_UHBR10:
+	case LINK_RATE_UHBR13_5:
+	case LINK_RATE_UHBR20:
+		break;
+	default:
+		valid_input = false;
+		break;
+	}
+
+	if (!valid_input) {
+		kfree(wr_buf);
+		DRM_DEBUG_DRIVER("Invalid Input value No HW will be programmed\n");
+		mutex_lock(&adev->dm.dc_lock);
+		dc_link_set_preferred_training_settings(dc, NULL, NULL, link, false);
+		mutex_unlock(&adev->dm.dc_lock);
+		return -EINVAL;
+	}
+
+	/* save user force lane_count, link_rate to preferred settings
+	 * spread spectrum will not be changed
+	 */
+	prefer_link_settings.link_spread = link->cur_link_settings.link_spread;
+	prefer_link_settings.use_link_rate_set = false;
+	prefer_link_settings.lane_count = param[0];
+	prefer_link_settings.link_rate = param[1];
+
+	/* skip immediate retrain, and train to new link setting after hotplug event triggered */
+	mutex_lock(&adev->dm.dc_lock);
+	dc_link_set_preferred_training_settings(dc, &prefer_link_settings, NULL, link, true);
+	mutex_unlock(&adev->dm.dc_lock);
+
+	mutex_lock(&aconnector->base.dev->mode_config.mutex);
+	aconnector->base.force = DRM_FORCE_OFF;
+	mutex_unlock(&aconnector->base.dev->mode_config.mutex);
+	drm_kms_helper_hotplug_event(aconnector->base.dev);
+
+	msleep(100);
+
+	mutex_lock(&aconnector->base.dev->mode_config.mutex);
+	aconnector->base.force = DRM_FORCE_UNSPECIFIED;
+	mutex_unlock(&aconnector->base.dev->mode_config.mutex);
+	drm_kms_helper_hotplug_event(aconnector->base.dev);
+
+	kfree(wr_buf);
+	return size;
+}
+
 /* function: get current DP PHY settings: voltage swing, pre-emphasis,
  * post-cursor2 (defined by VESA DP specification)
  *
@@ -2668,6 +2815,12 @@ static const struct file_operations dp_dsc_disable_passthrough_debugfs_fops = {
 	.llseek = default_llseek
 };
 
+static const struct file_operations dp_mst_link_settings_debugfs_fops = {
+	.owner = THIS_MODULE,
+	.write = dp_mst_link_setting,
+	.llseek = default_llseek
+};
+
 static const struct {
 	char *name;
 	const struct file_operations *fops;
@@ -2691,7 +2844,8 @@ static const struct {
 		{"dsc_disable_passthrough", &dp_dsc_disable_passthrough_debugfs_fops},
 		{"is_mst_connector", &dp_is_mst_connector_fops},
 		{"mst_progress_status", &dp_mst_progress_status_fops},
-		{"is_dpia_link", &is_dpia_link_fops}
+		{"is_dpia_link", &is_dpia_link_fops},
+		{"mst_link_settings", &dp_mst_link_settings_debugfs_fops}
 };
 
 static const struct {