drm/i915: fix handling of the disable_power_well module option

When this option is 0 (so the power well support is disabled) we are
supposed to enable all power wells once and don't disable them unless we
system suspend the device. Currently if the option is 0, we can call the
power well enable handlers multiple times, whenever their refcount
changes from 0->1. This may not be a problem for the HW, but it's not
logical and may trigger some warnings in the power well code which
doesn't expect this. So simply keep around a reference while we are
not system suspended to solve this. For simplicity mark the module
option read only, so we don't need to deal with re-enabling the feature
during runtime. If someone really needs that it could be added later in
a more proper way.

v2:
- fix typo in comment in intel_power_domains_suspend() (Patrik)
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1447775063-24438-1-git-send-email-imre.deak@intel.com

drivers/gpu/drm/i915/i915_params.c

@@ -125,7 +125,7 @@ module_param_named_unsafe(preliminary_hw_support, i915.preliminary_hw_support, i
 MODULE_PARM_DESC(preliminary_hw_support,
 	"Enable preliminary hardware support.");
 
-module_param_named_unsafe(disable_power_well, i915.disable_power_well, int, 0600);
+module_param_named_unsafe(disable_power_well, i915.disable_power_well, int, 0400);
 MODULE_PARM_DESC(disable_power_well,
 	"Disable the power well when possible (default: true)");
 

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -1413,7 +1413,7 @@ void intel_display_power_put(struct drm_i915_private *dev_priv,
 	for_each_power_well_rev(i, power_well, BIT(domain), power_domains) {
 		WARN_ON(!power_well->count);
 
-		if (!--power_well->count && i915.disable_power_well)
+		if (!--power_well->count)
 			intel_power_well_disable(dev_priv, power_well);
 	}
 
@@ -1854,6 +1854,10 @@ void intel_power_domains_fini(struct drm_i915_private *dev_priv)
 	 * the power well is not enabled, so just enable it in case
 	 * we're going to unload/reload. */
 	intel_display_set_init_power(dev_priv, true);
+
+	/* Remove the refcount we took to keep power well support disabled. */
+	if (!i915.disable_power_well)
+		intel_display_power_put(dev_priv, POWER_DOMAIN_INIT);
 }
 
 static void intel_power_domains_sync_hw(struct drm_i915_private *dev_priv)
@@ -2055,6 +2059,9 @@ void intel_power_domains_init_hw(struct drm_i915_private *dev_priv, bool resume)
 
 	/* For now, we need the power well to be always enabled. */
 	intel_display_set_init_power(dev_priv, true);
+	/* Disable power support if the user asked so. */
+	if (!i915.disable_power_well)
+		intel_display_power_get(dev_priv, POWER_DOMAIN_INIT);
 	intel_power_domains_sync_hw(dev_priv);
 	power_domains->initializing = false;
 }
@@ -2070,6 +2077,13 @@ void intel_power_domains_suspend(struct drm_i915_private *dev_priv)
 {
 	if (IS_SKYLAKE(dev_priv) || IS_KABYLAKE(dev_priv))
 		skl_display_core_uninit(dev_priv);
+
+	/*
+	 * Even if power well support was disabled we still want to disable
+	 * power wells while we are system suspended.
+	 */
+	if (!i915.disable_power_well)
+		intel_display_power_put(dev_priv, POWER_DOMAIN_INIT);
 }
 
 /**