[PATCH] usb: host: enable suspend-to-RAM control in userspace

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

In systems with both a main processor and a co-processor, asynchronous
controller management can lead to conflicts. For example, the main
processor might attempt to suspend a USB device while the co-processor
is actively transferring data. To address this, we introduce a new
sysfs entry, "disable_suspend2ram", which allows userspace to control
the suspend-to-RAM functionality of devices on a specific USB bus.
Since the userspace has visibility into the activities of both
processors, it can resolve potential conflicts.

Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
---
 Documentation/ABI/testing/sysfs-bus-usb | 10 +++++++
 drivers/usb/core/driver.c               | 12 ++++++++
 drivers/usb/core/sysfs.c                | 29 ++++++++++++++++++
 drivers/usb/host/xhci-plat.c            | 40 ++++++++++++++++++++++---
 include/linux/usb.h                     |  4 +++
 5 files changed, 91 insertions(+), 4 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
index 2b7108e21977..f6a4f496c8f6 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/disable_suspend2ram
+Date:		January 2024
+Contact:	Guan-Yu Lin <guanyulin@google.com>
+Description:
+		Disables "suspend-to-RAM" system power management in 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..c555e2b1ddda 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -1569,6 +1569,12 @@ int usb_suspend(struct device *dev, pm_message_t msg)
 	struct usb_device	*udev = to_usb_device(dev);
 	int r;
 
+	if (msg.event == PM_EVENT_SUSPEND && udev->bus->disable_suspend2ram) {
+		/* Skip "suspend-to-RAM" process under the same USB bus */
+		dev_dbg(dev, "suspend-to-RAM disabled, skipping dev_pm_ops.suspend\n");
+		return 0;
+	}
+
 	unbind_no_pm_drivers_interfaces(udev);
 
 	/* From now on we are sure all drivers support suspend/resume
@@ -1605,6 +1611,12 @@ int usb_resume(struct device *dev, pm_message_t msg)
 	struct usb_device	*udev = to_usb_device(dev);
 	int			status;
 
+	if (msg.event == PM_EVENT_RESUME && udev->bus->disable_suspend2ram) {
+		/* Skip "suspend-to-RAM" process under the same USB bus */
+		dev_dbg(dev, "suspend-to-RAM disabled, skipping dev_pm_ops.resume\n");
+		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..7a228ea95506 100644
--- a/drivers/usb/core/sysfs.c
+++ b/drivers/usb/core/sysfs.c
@@ -68,6 +68,34 @@ static ssize_t bMaxPower_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(bMaxPower);
 
+static ssize_t disable_suspend2ram_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->disable_suspend2ram));
+}
+
+static ssize_t disable_suspend2ram_store(struct device *dev,
+					 struct device_attribute *attr,
+					 const char *buf, size_t count)
+{
+	struct usb_device *udev = to_usb_device(dev);
+	bool val;
+	int rc;
+
+	if (kstrtobool(buf, &val) != 0)
+		return -EINVAL;
+	rc = usb_lock_device_interruptible(udev);
+	if (rc < 0)
+		return -EINTR;
+	udev->bus->disable_suspend2ram = !!(val);
+	usb_unlock_device(udev);
+	return count;
+}
+static DEVICE_ATTR_RW(disable_suspend2ram);
+
 static ssize_t configuration_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
@@ -984,6 +1012,7 @@ 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_disable_suspend2ram.attr,
 		NULL,
 };
 
diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
index f04fde19f551..86733249fcdc 100644
--- a/drivers/usb/host/xhci-plat.c
+++ b/drivers/usb/host/xhci-plat.c
@@ -436,12 +436,18 @@ void xhci_plat_remove(struct platform_device *dev)
 }
 EXPORT_SYMBOL_GPL(xhci_plat_remove);
 
-static int xhci_plat_suspend(struct device *dev)
+static int xhci_plat_suspend_common(struct device *dev, struct pm_message pmsg)
 {
 	struct usb_hcd	*hcd = dev_get_drvdata(dev);
 	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
 	int ret;
 
+	if (pmsg.event == PM_EVENT_SUSPEND && hcd->self.disable_suspend2ram) {
+		/* Skip "suspend-to-RAM" process under the same USB bus */
+		dev_dbg(dev, "suspend-to-RAM disabled, skipping dev_pm_ops.suspend\n");
+		return 0;
+	}
+
 	if (pm_runtime_suspended(dev))
 		pm_runtime_resume(dev);
 
@@ -464,12 +470,33 @@ static int xhci_plat_suspend(struct device *dev)
 	return 0;
 }
 
+static int xhci_plat_suspend(struct device *dev)
+{
+	return xhci_plat_suspend_common(dev, PMSG_SUSPEND);
+}
+
+static int xhci_plat_freeze(struct device *dev)
+{
+	return xhci_plat_suspend_common(dev, PMSG_FREEZE);
+}
+
+static int xhci_plat_poweroff(struct device *dev)
+{
+	return xhci_plat_suspend_common(dev, PMSG_HIBERNATE);
+}
+
 static int xhci_plat_resume_common(struct device *dev, struct pm_message pmsg)
 {
 	struct usb_hcd	*hcd = dev_get_drvdata(dev);
 	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
 	int ret;
 
+	if (pmsg.event == PM_EVENT_RESUME && hcd->self.disable_suspend2ram) {
+		/* Skip "suspend-to-RAM" process under the same USB bus */
+		dev_dbg(dev, "suspend-to-RAM disabled, skipping dev_pm_ops.resume\n");
+		return 0;
+	}
+
 	if (!device_may_wakeup(dev) && (xhci->quirks & XHCI_SUSPEND_RESUME_CLKS)) {
 		ret = clk_prepare_enable(xhci->clk);
 		if (ret)
@@ -510,6 +537,11 @@ static int xhci_plat_resume(struct device *dev)
 	return xhci_plat_resume_common(dev, PMSG_RESUME);
 }
 
+static int xhci_plat_thaw(struct device *dev)
+{
+	return xhci_plat_resume_common(dev, PMSG_THAW);
+}
+
 static int xhci_plat_restore(struct device *dev)
 {
 	return xhci_plat_resume_common(dev, PMSG_RESTORE);
@@ -539,9 +571,9 @@ static int __maybe_unused xhci_plat_runtime_resume(struct device *dev)
 const struct dev_pm_ops xhci_plat_pm_ops = {
 	.suspend = pm_sleep_ptr(xhci_plat_suspend),
 	.resume = pm_sleep_ptr(xhci_plat_resume),
-	.freeze = pm_sleep_ptr(xhci_plat_suspend),
-	.thaw = pm_sleep_ptr(xhci_plat_resume),
-	.poweroff = pm_sleep_ptr(xhci_plat_suspend),
+	.freeze = pm_sleep_ptr(xhci_plat_freeze),
+	.thaw = pm_sleep_ptr(xhci_plat_thaw),
+	.poweroff = pm_sleep_ptr(xhci_plat_poweroff),
 	.restore = pm_sleep_ptr(xhci_plat_restore),
 
 	SET_RUNTIME_PM_OPS(xhci_plat_runtime_suspend,
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 9e52179872a5..a3b8f799c5a4 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 disable_suspend2ram:1; /* Disables the "suspend-to-RAM" system
+					 * power management 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 */
 
-- 
2.43.0.594.gd9cf4e227d-goog