drm/i915/display: Add new interface for getting dc_state

To implement workaround for underrun on idle PSR HW issue (Wa_16025596647)
we need to have current configured DC state available. Add new interface
for this purpose.

Signed-off-by: Jouni Högander <[e-mail]>
Reviewed-by: Mika Kahola <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/gpu/drm/i915/display/intel_display_power.c

···
 	mutex_unlock(&power_domains->lock);
 }
 
+/**
+ * intel_display_power_get_current_dc_state - Set target dc state.
+ * @display: display device
+ *
+ * This function set the "DC off" power well target_dc_state,
+ * based upon this target_dc_stste, "DC off" power well will
+ * enable desired DC state.
+ */
+u32 intel_display_power_get_current_dc_state(struct intel_display *display)
+{
+	struct i915_power_well *power_well;
+	struct i915_power_domains *power_domains = &display->power.domains;
+	u32 current_dc_state = DC_STATE_DISABLE;
+
+	mutex_lock(&power_domains->lock);
+	power_well = lookup_power_well(display, SKL_DISP_DC_OFF);
+
+	if (drm_WARN_ON(display->drm, !power_well))
+		goto unlock;
+
+	current_dc_state = intel_power_well_is_enabled(display, power_well) ?
+		DC_STATE_DISABLE : power_domains->target_dc_state;
+
+unlock:
+	mutex_unlock(&power_domains->lock);
+
+	return current_dc_state;
+}
+
 static void __async_put_domains_mask(struct i915_power_domains *power_domains,
 				     struct intel_power_domain_mask *mask)
 {

drivers/gpu/drm/i915/display/intel_display_power.h

···
 void intel_display_power_resume(struct intel_display *display);
 void intel_display_power_set_target_dc_state(struct intel_display *display,
 					     u32 state);
+u32 intel_display_power_get_current_dc_state(struct intel_display *display);
 
 bool intel_display_power_is_enabled(struct intel_display *display,
 				    enum intel_display_power_domain domain);