drm/debug: Expose connector VRR monitor 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

v2:
* Fix the typo in max_vfreq (Manasi)
* Change the name of node to i915_vrr_info so we can add
other vrr info for more debug info (Manasi)
* Change the VRR capable to display Yes or No (Manasi)
* Fix indentation checkpatch errors (Manasi)
v3:
* Remove the unnecessary debug print (Manasi)
v4:
* Rebase
v5:
* Rename to vrr_range to match AMD debugfs
v6:
* Rebase (manasi)
v7:
* Fix cmpilation due to rebase
v8:
* Move debugfs node creation logic to DRM (Emil)
* Remove AMD specific logic (Emil)
v9:
* Separate patch for removal of AMD specific logic (Manasi)
Signed-off-by: Bhanuprakash Modem <bhanuprakash.modem@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Harry Wentland <harry.wentland@amd.com>
CC: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200622142519.16214-3-bhanuprakash.modem@intel.com

drivers/gpu/drm/drm_debugfs.c

@@ -376,6 +376,24 @@ static ssize_t edid_write(struct file *file, const char __user *ubuf,
 	return (ret) ? ret : len;
 }
 
+/*
+ * 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;
+
+	if (connector->status != connector_status_connected)
+		return -ENODEV;
+
+	seq_printf(m, "Min: %u\n", (u8)connector->display_info.monitor_range.min_vfreq);
+	seq_printf(m, "Max: %u\n", (u8)connector->display_info.monitor_range.max_vfreq);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(vrr_range);
+
 static const struct file_operations drm_edid_fops = {
 	.owner = THIS_MODULE,
 	.open = edid_open,
@@ -413,6 +431,10 @@ void drm_debugfs_connector_add(struct drm_connector *connector)
 	/* edid */
 	debugfs_create_file("edid_override", S_IRUGO | S_IWUSR, root, connector,
 			    &drm_edid_fops);
+
+	/* vrr range */
+	debugfs_create_file("vrr_range", S_IRUGO, root, connector,
+			    &vrr_range_fops);
 }
 
 void drm_debugfs_connector_remove(struct drm_connector *connector)