drm/i915: add intel_using_power_well

It returns true if we've requested to turn the power well on and it's
really on. It also returns true for all the previous gens.

For now there's just one caller, but I'm going to add more.
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -1227,8 +1227,8 @@ void assert_pipe(struct drm_i915_private *dev_priv,
 	if (pipe == PIPE_A && dev_priv->quirks & QUIRK_PIPEA_FORCE)
 		state = true;
 
-	if (IS_HASWELL(dev_priv->dev) && cpu_transcoder != TRANSCODER_EDP &&
-	    !(I915_READ(HSW_PWR_WELL_DRIVER) & HSW_PWR_WELL_ENABLE)) {
+	if (!intel_using_power_well(dev_priv->dev) &&
+	    cpu_transcoder != TRANSCODER_EDP) {
 		cur_state = false;
 	} else {
 		reg = PIPECONF(cpu_transcoder);

drivers/gpu/drm/i915/intel_drv.h

@@ -693,6 +693,7 @@ extern void intel_update_fbc(struct drm_device *dev);
 extern void intel_gpu_ips_init(struct drm_i915_private *dev_priv);
 extern void intel_gpu_ips_teardown(void);
 
+extern bool intel_using_power_well(struct drm_device *dev);
 extern void intel_init_power_well(struct drm_device *dev);
 extern void intel_set_power_well(struct drm_device *dev, bool enable);
 extern void intel_enable_gt_powersave(struct drm_device *dev);

drivers/gpu/drm/i915/intel_pm.c

@@ -4085,6 +4085,22 @@ void intel_init_clock_gating(struct drm_device *dev)
 	dev_priv->display.init_clock_gating(dev);
 }
 
+/**
+ * We should only use the power well if we explicitly asked the hardware to
+ * enable it, so check if it's enabled and also check if we've requested it to
+ * be enabled.
+ */
+bool intel_using_power_well(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	if (IS_HASWELL(dev))
+		return I915_READ(HSW_PWR_WELL_DRIVER) ==
+		       (HSW_PWR_WELL_ENABLE | HSW_PWR_WELL_STATE);
+	else
+		return true;
+}
+
 void intel_set_power_well(struct drm_device *dev, bool enable)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;