pmdomain: imx8mp-blk-ctrl: Keep gpc power domain on for system wakeup

Current design will power off all dependent GPC power domains in
imx8mp_blk_ctrl_suspend(), even though the user device has enabled
wakeup capability. The result is that wakeup function never works
for such device.

An example will be USB wakeup on i.MX8MP. PHY device '382f0040.usb-phy'
is attached to power domain 'hsioblk-usb-phy2' which is spawned by hsio
block control. A virtual power domain device 'genpd:3:32f10000.blk-ctrl'
is created to build connection with 'hsioblk-usb-phy2' and it depends on
GPC power domain 'usb-otg2'. If device '382f0040.usb-phy' enable wakeup,
only power domain 'hsioblk-usb-phy2' keeps on during system suspend,
power domain 'usb-otg2' is off all the time. So the wakeup event can't
happen.

In order to further establish a connection between the power domains
related to GPC and block control during system suspend, register a genpd
power on/off notifier for the power_dev. This allows us to prevent the GPC
power domain from being powered off, in case the block control power
domain is kept on to serve system wakeup.

Suggested-by: Ulf Hansson <[e-mail]>
Fixes: 556f5cf9568a ("soc: imx: add i.MX8MP HSIO blk-ctrl")
Cc: [e-mail]
Signed-off-by: Xu Yang <[e-mail]>
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/pmdomain/imx/imx8mp-blk-ctrl.c

···
 	struct icc_bulk_data paths[DOMAIN_MAX_PATHS];
 	struct device *power_dev;
 	struct imx8mp_blk_ctrl *bc;
+	struct notifier_block power_nb;
 	int num_paths;
 	int id;
 };
···
 	return 0;
 }
 
+static int imx8mp_blk_ctrl_gpc_notifier(struct notifier_block *nb,
+					unsigned long action, void *data)
+{
+	struct imx8mp_blk_ctrl_domain *domain =
+			container_of(nb, struct imx8mp_blk_ctrl_domain, power_nb);
+
+	if (action == GENPD_NOTIFY_PRE_OFF) {
+		if (domain->genpd.status == GENPD_STATE_ON)
+			return NOTIFY_BAD;
+	}
+
+	return NOTIFY_OK;
+}
+
 static struct lock_class_key blk_ctrl_genpd_lock_class;
 
 static int imx8mp_blk_ctrl_probe(struct platform_device *pdev)
···
 			goto cleanup_pds;
 		}
 
+		domain->power_nb.notifier_call = imx8mp_blk_ctrl_gpc_notifier;
+		ret = dev_pm_genpd_add_notifier(domain->power_dev, &domain->power_nb);
+		if (ret) {
+			dev_err_probe(dev, ret, "failed to add power notifier\n");
+			dev_pm_domain_detach(domain->power_dev, true);
+			goto cleanup_pds;
+		}
+
 		domain->genpd.name = data->name;
 		domain->genpd.power_on = imx8mp_blk_ctrl_power_on;
 		domain->genpd.power_off = imx8mp_blk_ctrl_power_off;
···
 		ret = pm_genpd_init(&domain->genpd, NULL, true);
 		if (ret) {
 			dev_err_probe(dev, ret, "failed to init power domain\n");
+			dev_pm_genpd_remove_notifier(domain->power_dev);
 			dev_pm_domain_detach(domain->power_dev, true);
 			goto cleanup_pds;
 		}
···
 cleanup_pds:
 	for (i--; i >= 0; i--) {
 		pm_genpd_remove(&bc->domains[i].genpd);
+		dev_pm_genpd_remove_notifier(bc->domains[i].power_dev);
 		dev_pm_domain_detach(bc->domains[i].power_dev, true);
 	}
 
···
 		struct imx8mp_blk_ctrl_domain *domain = &bc->domains[i];
 
 		pm_genpd_remove(&domain->genpd);
+		dev_pm_genpd_remove_notifier(domain->power_dev);
 		dev_pm_domain_detach(domain->power_dev, true);
 	}