drm/amd/display: add sysfs entry to read PSR residency from firmware

[Why]
Currently there aren't any methods to determine PSR state residency.

[How]
create a sysfs entry for reading residency and internally hook it up
to existing functionality of reading PSR residency from firmware.

[Hamza: dropped the link.h include and made checkpatch happy]
Signed-off-by: Shirish S <shirish.s@amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -2793,6 +2793,22 @@ static int psr_get(void *data, u64 *val)
 	return 0;
 }
 
+/*
+ *  Read PSR state residency
+ */
+static int psr_read_residency(void *data, u64 *val)
+{
+	struct amdgpu_dm_connector *connector = data;
+	struct dc_link *link = connector->dc_link;
+	u32 residency;
+
+	link_get_psr_residency(link, &residency);
+
+	*val = (u64)residency;
+
+	return 0;
+}
+
 /*
  * Set dmcub trace event IRQ enable or disable.
  * Usage to enable dmcub trace event IRQ: echo 1 > /sys/kernel/debug/dri/0/amdgpu_dm_dmcub_trace_event_en
@@ -2828,6 +2844,8 @@ DEFINE_DEBUGFS_ATTRIBUTE(dmcub_trace_event_state_fops, dmcub_trace_event_state_g
 			 dmcub_trace_event_state_set, "%llu\n");
 
 DEFINE_DEBUGFS_ATTRIBUTE(psr_fops, psr_get, NULL, "%llu\n");
+DEFINE_DEBUGFS_ATTRIBUTE(psr_residency_fops, psr_read_residency, NULL,
+			 "%llu\n");
 
 DEFINE_SHOW_ATTRIBUTE(current_backlight);
 DEFINE_SHOW_ATTRIBUTE(target_backlight);
@@ -2991,6 +3009,8 @@ void connector_debugfs_init(struct amdgpu_dm_connector *connector)
 	if (connector->base.connector_type == DRM_MODE_CONNECTOR_eDP) {
 		debugfs_create_file_unsafe("psr_capability", 0444, dir, connector, &psr_capability_fops);
 		debugfs_create_file_unsafe("psr_state", 0444, dir, connector, &psr_fops);
+		debugfs_create_file_unsafe("psr_residency", 0444, dir,
+					   connector, &psr_residency_fops);
 		debugfs_create_file("amdgpu_current_backlight_pwm", 0444, dir, connector,
 				    &current_backlight_fops);
 		debugfs_create_file("amdgpu_target_backlight_pwm", 0444, dir, connector,