drm/amd/display: Expose connector VRR range via debugfs

[Why]
It's useful to know the min and max vrr range for IGT testing.

[How]
Expose the min and max vfreq for the connector via a debugfs file
on the connector, "vrr_range".

Example usage: cat /sys/kernel/debug/dri/0/DP-1/vrr_range
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -671,6 +671,25 @@ static ssize_t dp_phy_test_pattern_debugfs_write(struct file *f, const char __us
 	return bytes_from_user;
 }
 
+/*
+ * 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
+ */
+static int vrr_range_show(struct seq_file *m, void *data)
+{
+	struct drm_connector *connector = m->private;
+	struct amdgpu_dm_connector *aconnector = to_amdgpu_dm_connector(connector);
+
+	if (connector->status != connector_status_connected)
+		return -ENODEV;
+
+	seq_printf(m, "Min: %u\n", (unsigned int)aconnector->min_vfreq);
+	seq_printf(m, "Max: %u\n", (unsigned int)aconnector->max_vfreq);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(vrr_range);
+
 static const struct file_operations dp_link_settings_debugfs_fops = {
 	.owner = THIS_MODULE,
 	.read = dp_link_settings_read,
@@ -697,7 +716,8 @@ static const struct {
 } dp_debugfs_entries[] = {
 		{"link_settings", &dp_link_settings_debugfs_fops},
 		{"phy_settings", &dp_phy_settings_debugfs_fop},
-		{"test_pattern", &dp_phy_test_pattern_fops}
+		{"test_pattern", &dp_phy_test_pattern_fops},
+		{"vrr_range", &vrr_range_fops}
 };
 
 int connector_debugfs_init(struct amdgpu_dm_connector *connector)