[PATCH] [RFC] usb: host: Allow userspace to control usb suspend flows

[Guan-Yu Lin <guanyulin@google.com>]

In a system with sub-system engaged, the controllers are controlled by
both the main processor and the co-processor. Chances are when the main
processor decides to suspend the USB device, the USB device might still
be used by the co-processor. In this scenario, we need a way to let
system know whether it can suspend the USB device or not. We introduce a
new sysfs entry "deprecate_device_pm" to allow userspace to control the
device power management functionality on demand. As the userspace should
possess the information of both the main processor and the co-processor,
it should be able to address the conflict mentioned above.

Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
---
 Documentation/ABI/testing/sysfs-bus-usb | 10 +++++++++
 drivers/usb/core/driver.c               | 18 ++++++++++++++++
 drivers/usb/core/sysfs.c                | 28 +++++++++++++++++++++++++
 drivers/usb/host/xhci-plat.c            | 20 ++++++++++++++++++
 include/linux/usb.h                     |  4 ++++
 5 files changed, 80 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
index 2b7108e21977..3f3d6c14201f 100644
--- a/Documentation/ABI/testing/sysfs-bus-usb
+++ b/Documentation/ABI/testing/sysfs-bus-usb
@@ -19,6 +19,16 @@ Description:
 		would be authorized by default.
 		The value can be 1 or 0. It's by default 1.
 
+What:		/sys/bus/usb/devices/usbX/deprecate_device_pm
+Date:		January 2024
+Contact:	Guan-Yu Lin <guanyulin@google.com>
+Description:
+		Deprecates the device power management functionality of USB devices
+		and their host contorller under this usb bus. The modification of
+		this entry should be done when the system is active to ensure the
+		correctness of system power state transitions.
+		The value can be 1 or 0. It's by default 0.
+
 What:		/sys/bus/usb/device/.../authorized
 Date:		July 2008
 KernelVersion:	2.6.26
diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index e02ba15f6e34..e03cf972160d 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -1569,6 +1569,15 @@ int usb_suspend(struct device *dev, pm_message_t msg)
 	struct usb_device	*udev = to_usb_device(dev);
 	int r;
 
+	/*
+	 * Skip the entire suspend process under the same usb bus if its sysfs
+	 * entry `deprecate_device_pm` is set.
+	 */
+	if (udev->bus->deprecate_device_pm) {
+		dev_vdbg(&udev->dev, "deprecating dev_pm_ops: %s\n", __func__);
+		return 0;
+	}
+
 	unbind_no_pm_drivers_interfaces(udev);
 
 	/* From now on we are sure all drivers support suspend/resume
@@ -1605,6 +1614,15 @@ int usb_resume(struct device *dev, pm_message_t msg)
 	struct usb_device	*udev = to_usb_device(dev);
 	int			status;
 
+	/*
+	 * Skip the entire resume process under the same usb bus if its sysfs
+	 * entry `deprecate_device_pm` is set.
+	 */
+	if (udev->bus->deprecate_device_pm) {
+		dev_vdbg(&udev->dev, "deprecating dev_pm_ops: %s\n", __func__);
+		return 0;
+	}
+
 	/* For all calls, take the device back to full power and
 	 * tell the PM core in case it was autosuspended previously.
 	 * Unbind the interfaces that will need rebinding later,
diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c
index 5d21718afb05..b4520e5c8974 100644
--- a/drivers/usb/core/sysfs.c
+++ b/drivers/usb/core/sysfs.c
@@ -68,6 +68,33 @@ static ssize_t bMaxPower_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(bMaxPower);
 
+static ssize_t deprecate_device_pm_show(struct device *dev,
+					struct device_attribute *attr, char *buf)
+{
+	struct usb_device *udev;
+
+	udev = to_usb_device(dev);
+	return sysfs_emit(buf, "%d\n", !!(udev->bus->deprecate_device_pm));
+}
+
+static ssize_t deprecate_device_pm_store(struct device *dev,
+					 struct device_attribute *attr,
+					 const char *buf, size_t count)
+{
+	struct usb_device	*udev = to_usb_device(dev);
+	int			val, rc;
+
+	if (sscanf(buf, "%d", &val) != 1 || val < 0 || val > 1)
+		return -EINVAL;
+	rc = usb_lock_device_interruptible(udev);
+	if (rc < 0)
+		return -EINTR;
+	udev->bus->deprecate_device_pm = !!(val);
+	usb_unlock_device(udev);
+	return count;
+}
+static DEVICE_ATTR_RW(deprecate_device_pm);
+
 static ssize_t configuration_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
@@ -984,6 +1011,7 @@ static DEVICE_ATTR_RW(interface_authorized_default);
 static struct attribute *usb_bus_attrs[] = {
 		&dev_attr_authorized_default.attr,
 		&dev_attr_interface_authorized_default.attr,
+		&dev_attr_deprecate_device_pm.attr,
 		NULL,
 };
 
diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
index f04fde19f551..bc05d83d1c0b 100644
--- a/drivers/usb/host/xhci-plat.c
+++ b/drivers/usb/host/xhci-plat.c
@@ -442,6 +442,15 @@ static int xhci_plat_suspend(struct device *dev)
 	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
 	int ret;
 
+	/*
+	 * Skip the entire suspend process under the same usb bus if its sysfs
+	 * entry `deprecate_device_pm` is set.
+	 */
+	if (hcd->self.deprecate_device_pm) {
+		dev_vdbg(dev, "deprecating dev_pm_ops: %s\n", __func__);
+		return 0;
+	}
+
 	if (pm_runtime_suspended(dev))
 		pm_runtime_resume(dev);
 
@@ -507,6 +516,17 @@ static int xhci_plat_resume_common(struct device *dev, struct pm_message pmsg)
 
 static int xhci_plat_resume(struct device *dev)
 {
+	struct usb_hcd	*hcd = dev_get_drvdata(dev);
+
+	/*
+	 * Skip the entire resume process under the same usb bus if its sysfs
+	 * entry `deprecate_device_pm` is set.
+	 */
+	if (hcd->self.deprecate_device_pm) {
+		dev_vdbg(dev, "deprecating dev_pm_ops: %s\n", __func__);
+		return 0;
+	}
+
 	return xhci_plat_resume_common(dev, PMSG_RESUME);
 }
 
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 9e52179872a5..1a1873104663 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -465,6 +465,10 @@ struct usb_bus {
 					 * the ep queue on a short transfer
 					 * with the URB_SHORT_NOT_OK flag set.
 					 */
+	unsigned deprecate_device_pm:1; /* Deprecates the device power management
+					 * functionality of USB devices on this
+					 * bus and their hcd.
+					 */
 	unsigned no_sg_constraint:1;	/* no sg constraint */
 	unsigned sg_tablesize;		/* 0 or largest number of sg list entries */
 
-- 
2.43.0.429.g432eaa2c6b-goog