drm/i915: Add comments explaining the vdd on/off functions

Jani wanted some comments to explain why we call certain vdd on/off
functions in certain places.

v2: Make the comments more thorough (Imre)

Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 0d468e6ad3fc67d3ccc0f842d50724873ce19438..97c5a0d11f6f5dc8e92d4f2fac5b193d948dbfda 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1354,6 +1354,11 @@ static  u32 ironlake_get_pp_control(struct intel_dp *intel_dp)
        return control;
 }
 
+/*
+ * Must be paired with edp_panel_vdd_off().
+ * Must hold pps_mutex around the whole on/off sequence.
+ * Can be nested with intel_edp_panel_vdd_{on,off}() calls.
+ */
 static bool edp_panel_vdd_on(struct intel_dp *intel_dp)
 {
        struct drm_device *dev = intel_dp_to_dev(intel_dp);
@@ -1404,6 +1409,13 @@ static bool edp_panel_vdd_on(struct intel_dp *intel_dp)
        return need_to_disable;
 }
 
+/*
+ * Must be paired with intel_edp_panel_vdd_off() or
+ * intel_edp_panel_off().
+ * Nested calls to these functions are not allowed since
+ * we drop the lock. Caller must use some higher level
+ * locking to prevent nested calls from other threads.
+ */
 void intel_edp_panel_vdd_on(struct intel_dp *intel_dp)
 {
        bool vdd;
@@ -1482,6 +1494,11 @@ static void edp_panel_vdd_schedule_off(struct intel_dp *intel_dp)
        schedule_delayed_work(&intel_dp->panel_vdd_work, delay);
 }
 
+/*
+ * Must be paired with edp_panel_vdd_on().
+ * Must hold pps_mutex around the whole on/off sequence.
+ * Can be nested with intel_edp_panel_vdd_{on,off}() calls.
+ */
 static void edp_panel_vdd_off(struct intel_dp *intel_dp, bool sync)
 {
        struct drm_i915_private *dev_priv =
@@ -1502,6 +1519,12 @@ static void edp_panel_vdd_off(struct intel_dp *intel_dp, bool sync)
                edp_panel_vdd_schedule_off(intel_dp);
 }
 
+/*
+ * Must be paired with intel_edp_panel_vdd_on().
+ * Nested calls to these functions are not allowed since
+ * we drop the lock. Caller must use some higher level
+ * locking to prevent nested calls from other threads.
+ */
 static void intel_edp_panel_vdd_off(struct intel_dp *intel_dp, bool sync)
 {
        if (!is_edp(intel_dp))
@@ -4373,6 +4396,10 @@ void intel_dp_encoder_destroy(struct drm_encoder *encoder)
        drm_encoder_cleanup(encoder);
        if (is_edp(intel_dp)) {
                cancel_delayed_work_sync(&intel_dp->panel_vdd_work);
+               /*
+                * vdd might still be enabled do to the delayed vdd off.
+                * Make sure vdd is actually turned off here.
+                */
                pps_lock(intel_dp);
                edp_panel_vdd_off_sync(intel_dp);
                pps_unlock(intel_dp);
@@ -4392,6 +4419,10 @@ static void intel_dp_encoder_suspend(struct intel_encoder *intel_encoder)
        if (!is_edp(intel_dp))
                return;
 
+       /*
+        * vdd might still be enabled do to the delayed vdd off.
+        * Make sure vdd is actually turned off here.
+        */
        pps_lock(intel_dp);
        edp_panel_vdd_off_sync(intel_dp);
        pps_unlock(intel_dp);
@@ -5095,6 +5126,10 @@ intel_dp_init_connector(struct intel_digital_port *intel_dig_port,
                drm_dp_aux_unregister(&intel_dp->aux);
                if (is_edp(intel_dp)) {
                        cancel_delayed_work_sync(&intel_dp->panel_vdd_work);
+                       /*
+                        * vdd might still be enabled do to the delayed vdd off.
+                        * Make sure vdd is actually turned off here.
+                        */
                        pps_lock(intel_dp);
                        edp_panel_vdd_off_sync(intel_dp);
                        pps_unlock(intel_dp);