drm/i915: fix WARNs when reading DDI state while suspended

If runtime PM is enabled and we unset all modes, we will runtime
suspend after __intel_set_mode() , then function
intel_modeset_check_state() will try to read the HW state while it is
suspended and trigger lots of WARNs because it shouldn't be reading
registers.

So on this patch we make intel_ddi_connector_get_hw_state() return
false in case the power domain is disabled, and we also make
intel_display_power_enabled() return false in case the device is
suspended. Notice that we can't just use
intel_display_power_enabled_sw() because while the driver is being
initialized the power domain refcounts are not reflecting the real
state of the hardware.

Just for reference, I have previously published an alternate patch for
this problem, called "drm/i915: get runtime PM at intel_set_mode".

Testcase: igt/pm_pc8
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ddi.c

@@ -1108,8 +1108,13 @@ bool intel_ddi_connector_get_hw_state(struct intel_connector *intel_connector)
 	enum port port = intel_ddi_get_encoder_port(intel_encoder);
 	enum pipe pipe = 0;
 	enum transcoder cpu_transcoder;
+	enum intel_display_power_domain power_domain;
 	uint32_t tmp;
 
+	power_domain = intel_display_port_power_domain(intel_encoder);
+	if (!intel_display_power_enabled(dev_priv, power_domain))
+		return false;
+
 	if (!intel_encoder->get_hw_state(intel_encoder, &pipe))
 		return false;
 

drivers/gpu/drm/i915/intel_pm.c

@@ -5280,6 +5280,9 @@ bool intel_display_power_enabled(struct drm_i915_private *dev_priv,
 	bool is_enabled;
 	int i;
 
+	if (dev_priv->pm.suspended)
+		return false;
+
 	power_domains = &dev_priv->power_domains;
 
 	is_enabled = true;