[PATCH RFC] pmdomain: core: add support for writeble power domain state

[Kamlesh Gurudasani <kamlesh@ti.com>]

Add support for writeable power domain states from debugfs.

Defining GENPD_ALLOW_WRITE_DEBUGFS will enable writeable pd_state
node in debugfs.

Signed-off-by: Kamlesh Gurudasani <kamlesh@ti.com>
---
This has turn out to be really helpful when debugging SCMI protocol
for power domain management.

Reference has been taken from clock framework which provides similar
CLOCK_ALLOW_WRITE_DEBUGFS, which helps to test clocks from debugfs.
---
 drivers/pmdomain/core.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)

diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
index 9b2f28b34bb5..6aba0c672da0 100644
--- a/drivers/pmdomain/core.c
+++ b/drivers/pmdomain/core.c
@@ -1298,6 +1298,60 @@ late_initcall_sync(genpd_power_off_unused);
 
 #ifdef CONFIG_PM_SLEEP
 
+#ifdef GENPD_ALLOW_WRITE_DEBUGFS
+/*
+ * This can be dangerous, therefore don't provide any real compile time
+ * configuration option for this feature.
+ * People who want to use this will need to modify the source code directly.
+ */
+static int genpd_state_set(void *data, u64 val)
+{
+
+	struct generic_pm_domain *genpd = data;
+	int ret = 0;
+
+	ret = genpd_lock_interruptible(genpd);
+	if (ret)
+		return -ERESTARTSYS;
+
+	if (val == 1) {
+		genpd->power_on(genpd);
+		genpd->status = GENPD_STATE_ON;
+	} else if (val == 0) {
+		genpd->power_off(genpd);
+		genpd->status = GENPD_STATE_OFF;
+	}
+
+	genpd_unlock(genpd);
+	return 0;
+}
+
+#define pd_state_mode	0644
+
+static int genpd_state_get(void *data, u64 *val)
+{
+
+	struct generic_pm_domain *genpd = data;
+	int ret = 0;
+
+	ret = genpd_lock_interruptible(genpd);
+	if (ret)
+		return -ERESTARTSYS;
+
+	if (genpd->status == GENPD_STATE_OFF)
+		*val = 0;
+	else
+		*val = 1;
+
+	genpd_unlock(genpd);
+	return ret;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(pd_state_fops, genpd_state_get,
+			 genpd_state_set, "%llu\n");
+
+#endif /* GENPD_ALLOW_WRITE_DEBUGFS */
+
 /**
  * genpd_sync_power_off - Synchronously power off a PM domain and its parents.
  * @genpd: PM domain to power off, if possible.
@@ -3639,6 +3693,11 @@ static void genpd_debug_add(struct generic_pm_domain *genpd)
 	if (genpd->set_performance_state)
 		debugfs_create_file("perf_state", 0444,
 				    d, genpd, &perf_state_fops);
+#ifdef GENPD_ALLOW_WRITE_DEBUGFS
+	debugfs_create_file("pd_state", 0644, d, genpd,
+			    &pd_state_fops);
+#endif /* GENPD_ALLOW_WRITE_DEBUGFS */
+
 }
 
 static int __init genpd_debug_init(void)
@@ -3653,6 +3712,24 @@ static int __init genpd_debug_init(void)
 	list_for_each_entry(genpd, &gpd_list, gpd_list_node)
 		genpd_debug_add(genpd);
 
+#ifdef GENPD_ALLOW_WRITE_DEBUGFS
+	pr_warn("\n");
+	pr_warn("********************************************************************\n");
+	pr_warn("**     NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE           **\n");
+	pr_warn("**                                                                **\n");
+	pr_warn("**  WRITEABLE POWER DOMAIN STATE DEBUGFS SUPPORT HAS BEEN ENABLED **\n");
+	pr_warn("**  IN THIS KERNEL                                                **\n");
+	pr_warn("** This means that this kernel is built to expose pd operations   **\n");
+	pr_warn("** such as enabling, disabling, etc.                              **\n");
+	pr_warn("** to userspace, which may compromise security on your system.    **\n");
+	pr_warn("**                                                                **\n");
+	pr_warn("** If you see this message and you are not debugging the          **\n");
+	pr_warn("** kernel, report this immediately to your vendor!                **\n");
+	pr_warn("**                                                                **\n");
+	pr_warn("**     NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE           **\n");
+	pr_warn("********************************************************************\n");
+#endif /* GENPD_ALLOW_WRITE_DEBUGFS */
+
 	return 0;
 }
 late_initcall(genpd_debug_init);

---
base-commit: d4b0fd87ff0d4338b259dc79b2b3c6f7e70e8afa
change-id: 20250221-pm-debug-0824da30890f

Best regards,
-- 
Kamlesh Gurudasani <kamlesh@ti.com>