[RFC 8/9] PCI/pwrctl: add PCI power control core code

[Bartosz Golaszewski <brgl@bgdev.pl>]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Some PCI devices must be powered-on before they can be detected on the
bus. Introduce a simple framework reusing the existing PCI OF
infrastructure.

The way this works is: a DT node representing a PCI device connected to
the port can be matched against its power control platform driver. If
the match succeeds, the driver is responsible for powering-up the device
and calling pcie_pwrctl_device_enable() which will trigger a PCI bus
rescan as well as subscribe to PCI bus notifications.

When the device is detected and created, we'll make it consume the same
DT node that the platform device did. When the device is bound, we'll
create a device link between it and the parent power control device.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/pci/Kconfig         |  1 +
 drivers/pci/Makefile        |  1 +
 drivers/pci/pwrctl/Kconfig  |  8 ++++
 drivers/pci/pwrctl/Makefile |  3 ++
 drivers/pci/pwrctl/core.c   | 82 +++++++++++++++++++++++++++++++++++++
 include/linux/pci-pwrctl.h  | 24 +++++++++++
 6 files changed, 119 insertions(+)
 create mode 100644 drivers/pci/pwrctl/Kconfig
 create mode 100644 drivers/pci/pwrctl/Makefile
 create mode 100644 drivers/pci/pwrctl/core.c
 create mode 100644 include/linux/pci-pwrctl.h

diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
index 74147262625b..5b9b84f8774f 100644
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -291,5 +291,6 @@ source "drivers/pci/hotplug/Kconfig"
 source "drivers/pci/controller/Kconfig"
 source "drivers/pci/endpoint/Kconfig"
 source "drivers/pci/switch/Kconfig"
+source "drivers/pci/pwrctl/Kconfig"
 
 endif
diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
index cc8b4e01e29d..6ae202d950f8 100644
--- a/drivers/pci/Makefile
+++ b/drivers/pci/Makefile
@@ -9,6 +9,7 @@ obj-$(CONFIG_PCI)		+= access.o bus.o probe.o host-bridge.o \
 
 obj-$(CONFIG_PCI)		+= msi/
 obj-$(CONFIG_PCI)		+= pcie/
+obj-$(CONFIG_PCI)		+= pwrctl/
 
 ifdef CONFIG_PCI
 obj-$(CONFIG_PROC_FS)		+= proc.o
diff --git a/drivers/pci/pwrctl/Kconfig b/drivers/pci/pwrctl/Kconfig
new file mode 100644
index 000000000000..e2dc5e5d2af1
--- /dev/null
+++ b/drivers/pci/pwrctl/Kconfig
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0
+
+menu "PCI Power control drivers"
+
+config PCI_PWRCTL
+	bool
+
+endmenu
diff --git a/drivers/pci/pwrctl/Makefile b/drivers/pci/pwrctl/Makefile
new file mode 100644
index 000000000000..4381cfbf3f21
--- /dev/null
+++ b/drivers/pci/pwrctl/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_PCI_PWRCTL)		+= core.o
diff --git a/drivers/pci/pwrctl/core.c b/drivers/pci/pwrctl/core.c
new file mode 100644
index 000000000000..312e6fe95c31
--- /dev/null
+++ b/drivers/pci/pwrctl/core.c
@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2024 Linaro Ltd.
+ */
+
+#include <linux/device.h>
+#include <linux/export.h>
+#include <linux/kernel.h>
+#include <linux/pci.h>
+#include <linux/pci-pwrctl.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+
+static int pci_pwrctl_notify(struct notifier_block *nb, unsigned long action,
+			     void *data)
+{
+	struct pci_pwrctl *pwrctl = container_of(nb, struct pci_pwrctl, nb);
+	struct device *dev = data;
+
+	if (dev_fwnode(dev) != dev_fwnode(pwrctl->dev))
+		return NOTIFY_DONE;
+
+	switch (action) {
+	case BUS_NOTIFY_ADD_DEVICE:
+		device_set_of_node_from_dev(dev, pwrctl->dev);
+		break;
+	case BUS_NOTIFY_BOUND_DRIVER:
+		pwrctl->link = device_link_add(dev, pwrctl->dev,
+					       DL_FLAG_AUTOREMOVE_CONSUMER);
+		if (!pwrctl->link)
+			dev_err(pwrctl->dev, "Failed to add device link\n");
+		break;
+	case BUS_NOTIFY_UNBOUND_DRIVER:
+		device_link_del(pwrctl->link);
+		break;
+	}
+
+	return NOTIFY_DONE;
+}
+
+int pci_pwrctl_device_enable(struct pci_pwrctl *pwrctl)
+{
+	if (!pwrctl->dev)
+		return -ENODEV;
+
+	pwrctl->nb.notifier_call = pci_pwrctl_notify;
+	bus_register_notifier(&pci_bus_type, &pwrctl->nb);
+
+	pci_lock_rescan_remove();
+	pci_rescan_bus(to_pci_dev(pwrctl->dev->parent)->bus);
+	pci_unlock_rescan_remove();
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(pci_pwrctl_device_enable);
+
+void pci_pwrctl_device_disable(struct pci_pwrctl *pwrctl)
+{
+	bus_unregister_notifier(&pci_bus_type, &pwrctl->nb);
+}
+EXPORT_SYMBOL_GPL(pci_pwrctl_device_disable);
+
+static void devm_pci_pwrctl_device_disable(void *data)
+{
+	struct pci_pwrctl *pwrctl = data;
+
+	pci_pwrctl_device_disable(pwrctl);
+}
+
+int devm_pci_pwrctl_device_enable(struct device *dev,
+				  struct pci_pwrctl *pwrctl)
+{
+	int ret;
+
+	ret = pci_pwrctl_device_enable(pwrctl);
+	if (ret)
+		return ret;
+
+	return devm_add_action_or_reset(dev, devm_pci_pwrctl_device_disable,
+					pwrctl);
+}
+EXPORT_SYMBOL_GPL(devm_pci_pwrctl_device_enable);
diff --git a/include/linux/pci-pwrctl.h b/include/linux/pci-pwrctl.h
new file mode 100644
index 000000000000..8d16d27cbfeb
--- /dev/null
+++ b/include/linux/pci-pwrctl.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2024 Linaro Ltd.
+ */
+
+#ifndef __PCI_PWRCTL_H__
+#define __PCI_PWRCTL_H__
+
+#include <linux/notifier.h>
+
+struct device;
+
+struct pci_pwrctl {
+	struct notifier_block nb;
+	struct device *dev;
+	struct device_link *link;
+};
+
+int pci_pwrctl_device_enable(struct pci_pwrctl *pwrctl);
+void pci_pwrctl_device_disable(struct pci_pwrctl *pwrctl);
+int devm_pci_pwrctl_device_enable(struct device *dev,
+				  struct pci_pwrctl *pwrctl);
+
+#endif /* __PCI_PWRCTL_H__ */
-- 
2.40.1