drm/amd/display: Add connector debugfs for "output_bpc"

[Why]
This will be useful for verifying whether we enter the correct output
color depth from IGT.

[How]
Locks the connector and associated CRTC if available and outputs
the current and maximum output bpc values.

Example:

cat /sys/kernel/debug/dri/0/DP-1/output_bpc
Current: 8
Maximum: 10

v2: Drop unneeded connector status check
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: David Francis <David.Francis@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -672,6 +672,71 @@ static ssize_t dp_phy_test_pattern_debugfs_write(struct file *f, const char __us
 	return bytes_from_user;
 }
 
+/*
+ * Returns the current and maximum output bpc for the connector.
+ * Example usage: cat /sys/kernel/debug/dri/0/DP-1/output_bpc
+ */
+static int output_bpc_show(struct seq_file *m, void *data)
+{
+	struct drm_connector *connector = m->private;
+	struct drm_device *dev = connector->dev;
+	struct drm_crtc *crtc = NULL;
+	struct dm_crtc_state *dm_crtc_state = NULL;
+	int res = -ENODEV;
+	unsigned int bpc;
+
+	mutex_lock(&dev->mode_config.mutex);
+	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
+
+	if (connector->state == NULL)
+		goto unlock;
+
+	crtc = connector->state->crtc;
+	if (crtc == NULL)
+		goto unlock;
+
+	drm_modeset_lock(&crtc->mutex, NULL);
+	if (crtc->state == NULL)
+		goto unlock;
+
+	dm_crtc_state = to_dm_crtc_state(crtc->state);
+	if (dm_crtc_state->stream == NULL)
+		goto unlock;
+
+	switch (dm_crtc_state->stream->timing.display_color_depth) {
+	case COLOR_DEPTH_666:
+		bpc = 6;
+		break;
+	case COLOR_DEPTH_888:
+		bpc = 8;
+		break;
+	case COLOR_DEPTH_101010:
+		bpc = 10;
+		break;
+	case COLOR_DEPTH_121212:
+		bpc = 12;
+		break;
+	case COLOR_DEPTH_161616:
+		bpc = 16;
+		break;
+	default:
+		goto unlock;
+	}
+
+	seq_printf(m, "Current: %u\n", bpc);
+	seq_printf(m, "Maximum: %u\n", connector->display_info.bpc);
+	res = 0;
+
+unlock:
+	if (crtc)
+		drm_modeset_unlock(&crtc->mutex);
+
+	drm_modeset_unlock(&dev->mode_config.connection_mutex);
+	mutex_unlock(&dev->mode_config.mutex);
+
+	return res;
+}
+
 /*
  * Returns the min and max vrr vfreq through the connector's debugfs file.
  * Example usage: cat /sys/kernel/debug/dri/0/DP-1/vrr_range
@@ -730,8 +795,6 @@ static ssize_t dp_sdp_message_debugfs_write(struct file *f, const char __user *b
 	return write_size;
 }
 
-DEFINE_SHOW_ATTRIBUTE(vrr_range);
-
 static ssize_t dp_dpcd_address_write(struct file *f, const char __user *buf,
 				 size_t size, loff_t *pos)
 {
@@ -814,6 +877,9 @@ static ssize_t dp_dpcd_data_read(struct file *f, char __user *buf,
 	return read_size - r;
 }
 
+DEFINE_SHOW_ATTRIBUTE(output_bpc);
+DEFINE_SHOW_ATTRIBUTE(vrr_range);
+
 static const struct file_operations dp_link_settings_debugfs_fops = {
 	.owner = THIS_MODULE,
 	.read = dp_link_settings_read,
@@ -866,6 +932,7 @@ static const struct {
 		{"link_settings", &dp_link_settings_debugfs_fops},
 		{"phy_settings", &dp_phy_settings_debugfs_fop},
 		{"test_pattern", &dp_phy_test_pattern_fops},
+		{"output_bpc", &output_bpc_fops},
 		{"vrr_range", &vrr_range_fops},
 		{"sdp_message", &sdp_message_fops},
 		{"aux_dpcd_address", &dp_dpcd_address_debugfs_fops},