PM / domains: Add pd_ignore_unused to keep power domains enabled

Keep all power-domains already enabled by bootloader on, even if no
driver has claimed them. This is useful for debug and development, but
should not be needed on a platform with proper driver support.
Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/kernel-parameters.txt

@@ -2558,6 +2558,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
 	pcmv=		[HW,PCMCIA] BadgePAD 4
 
+	pd_ignore_unused
+			[PM]
+			Keep all power-domains already enabled by bootloader on,
+			even if no driver has claimed them. This is useful
+			for debug and development, but should not be
+			needed on a platform with proper driver support.
+
 	pd.		[PARIDE]
 			See Documentation/blockdev/paride.txt.
 

drivers/base/power/domain.c

@@ -705,6 +705,14 @@ static int pm_genpd_runtime_resume(struct device *dev)
 	return 0;
 }
 
+static bool pd_ignore_unused;
+static int __init pd_ignore_unused_setup(char *__unused)
+{
+	pd_ignore_unused = true;
+	return 1;
+}
+__setup("pd_ignore_unused", pd_ignore_unused_setup);
+
 /**
  * pm_genpd_poweroff_unused - Power off all PM domains with no devices in use.
  */
@@ -712,6 +720,11 @@ void pm_genpd_poweroff_unused(void)
 {
 	struct generic_pm_domain *genpd;
 
+	if (pd_ignore_unused) {
+		pr_warn("genpd: Not disabling unused power domains\n");
+		return;
+	}
+
 	mutex_lock(&gpd_list_lock);
 
 	list_for_each_entry(genpd, &gpd_list, gpd_list_node)