usb: host: enable USB offload during system sleep

Sharing a USB controller with another entity via xhci-sideband driver
creates power management complexities. To prevent the USB controller
from being inadvertently deactivated while in use by the other entity, a
usage-count based mechanism is implemented. This allows the system to
manage power effectively, ensuring the controller remains available
whenever needed.
In order to maintain full functionality of an offloaded USB devices,
several changes are made within the suspend flow of such devices:
- skip usb_suspend_device() so that the port/hub are still active for
  USB transfers via offloaded path.
- not suspending the endpoints which are used by USB interfaces marked
  with needs_remote_wakeup. Namely, skip usb_suspend_interface() and
  usb_hcd_flush_endpoint() on associated USB interfaces. This reserves a
  pending interrupt urb during system suspend for handling the interrupt
  transfer, which is necessary since remote wakeup doesn't apply in the
  offloaded USB devices when controller is still active.
- not flushing the endpoints of actively offloaded USB devices. Given
  that the USB devices is used by another entity, unilaterally flush the
  endpoint might lead to unexpected behavior on another entity.
- not suspending the xhci controller. This is done by skipping the
  suspend/resume callbacks in the xhci platform driver.

Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
Link: https://lore.kernel.org/r/20250911142051.90822-5-guanyulin@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250911142051.90822-5-guanyulin@google.com

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 25358cf3e324d623f9b32dd298e3f9f9477aa6f7..6418cfb0fb379f14f3071dbe5b01d9cb9cb4030b 100644 (file)
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -1420,11 +1420,28 @@ static int usb_suspend_both(struct usb_device *udev, pm_message_t msg)
                        udev->state == USB_STATE_SUSPENDED)
                goto done;
 
+       if (msg.event == PM_EVENT_SUSPEND && usb_offload_check(udev)) {
+               dev_dbg(&udev->dev, "device offloaded, skip suspend.\n");
+               udev->offload_at_suspend = 1;
+       }
+
        /* Suspend all the interfaces and then udev itself */
        if (udev->actconfig) {
                n = udev->actconfig->desc.bNumInterfaces;
                for (i = n - 1; i >= 0; --i) {
                        intf = udev->actconfig->interface[i];
+                       /*
+                        * Don't suspend interfaces with remote wakeup while
+                        * the controller is active. This preserves pending
+                        * interrupt urbs, allowing interrupt events to be
+                        * handled during system suspend.
+                        */
+                       if (udev->offload_at_suspend &&
+                           intf->needs_remote_wakeup) {
+                               dev_dbg(&intf->dev,
+                                       "device offloaded, skip suspend.\n");
+                               continue;
+                       }
                        status = usb_suspend_interface(udev, intf, msg);
 
                        /* Ignore errors during system sleep transitions */
@@ -1435,7 +1452,8 @@ static int usb_suspend_both(struct usb_device *udev, pm_message_t msg)
                }
        }
        if (status == 0) {
-               status = usb_suspend_device(udev, msg);
+               if (!udev->offload_at_suspend)
+                       status = usb_suspend_device(udev, msg);
 
                /*
                 * Ignore errors from non-root-hub devices during
@@ -1480,9 +1498,11 @@ static int usb_suspend_both(struct usb_device *udev, pm_message_t msg)
         */
        } else {
                udev->can_submit = 0;
-               for (i = 0; i < 16; ++i) {
-                       usb_hcd_flush_endpoint(udev, udev->ep_out[i]);
-                       usb_hcd_flush_endpoint(udev, udev->ep_in[i]);
+               if (!udev->offload_at_suspend) {
+                       for (i = 0; i < 16; ++i) {
+                               usb_hcd_flush_endpoint(udev, udev->ep_out[i]);
+                               usb_hcd_flush_endpoint(udev, udev->ep_in[i]);
+                       }
                }
        }
 
@@ -1524,17 +1544,35 @@ static int usb_resume_both(struct usb_device *udev, pm_message_t msg)
        udev->can_submit = 1;
 
        /* Resume the device */
-       if (udev->state == USB_STATE_SUSPENDED || udev->reset_resume)
-               status = usb_resume_device(udev, msg);
+       if (udev->state == USB_STATE_SUSPENDED || udev->reset_resume) {
+               if (!udev->offload_at_suspend)
+                       status = usb_resume_device(udev, msg);
+               else
+                       dev_dbg(&udev->dev,
+                               "device offloaded, skip resume.\n");
+       }
 
        /* Resume the interfaces */
        if (status == 0 && udev->actconfig) {
                for (i = 0; i < udev->actconfig->desc.bNumInterfaces; i++) {
                        intf = udev->actconfig->interface[i];
+                       /*
+                        * Interfaces with remote wakeup aren't suspended
+                        * while the controller is active. This preserves
+                        * pending interrupt urbs, allowing interrupt events
+                        * to be handled during system suspend.
+                        */
+                       if (udev->offload_at_suspend &&
+                           intf->needs_remote_wakeup) {
+                               dev_dbg(&intf->dev,
+                                       "device offloaded, skip resume.\n");
+                               continue;
+                       }
                        usb_resume_interface(udev, intf, msg,
                                        udev->reset_resume);
                }
        }
+       udev->offload_at_suspend = 0;
        usb_mark_last_busy(udev);
 
  done:

diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
index df2e942ad5f7b4d8f450ecd1d6fba0200b7f3d87..3a56d8f9451924540d9b40fb07d1ea9492656a35 100644 (file)
--- a/drivers/usb/host/xhci-plat.c
+++ b/drivers/usb/host/xhci-plat.c
@@ -20,6 +20,7 @@
 #include <linux/acpi.h>
 #include <linux/usb/of.h>
 #include <linux/reset.h>
+#include <linux/usb/xhci-sideband.h>
 
 #include "xhci.h"
 #include "xhci-plat.h"
@@ -484,6 +485,15 @@ static int xhci_plat_suspend_common(struct device *dev)
 
 static int xhci_plat_suspend(struct device *dev)
 {
+       struct usb_hcd  *hcd = dev_get_drvdata(dev);
+       struct xhci_plat_priv *priv = hcd_to_xhci_priv(hcd);
+
+       if (xhci_sideband_check(hcd)) {
+               priv->sideband_at_suspend = 1;
+               dev_dbg(dev, "sideband instance active, skip suspend.\n");
+               return 0;
+       }
+
        return xhci_plat_suspend_common(dev);
 }
 
@@ -536,6 +546,15 @@ disable_clks:
 
 static int xhci_plat_resume(struct device *dev)
 {
+       struct usb_hcd  *hcd = dev_get_drvdata(dev);
+       struct xhci_plat_priv *priv = hcd_to_xhci_priv(hcd);
+
+       if (priv->sideband_at_suspend) {
+               priv->sideband_at_suspend = 0;
+               dev_dbg(dev, "sideband instance active, skip resume.\n");
+               return 0;
+       }
+
        return xhci_plat_resume_common(dev, false);
 }
 

diff --git a/drivers/usb/host/xhci-plat.h b/drivers/usb/host/xhci-plat.h
index fe4f95e690fa69a60ea8c7671cda41634ab86e80..2b32a93d2b7604ba83442a839438764e1ba2e382 100644 (file)
--- a/drivers/usb/host/xhci-plat.h
+++ b/drivers/usb/host/xhci-plat.h
@@ -16,6 +16,7 @@ struct xhci_plat_priv {
        const char *firmware_name;
        unsigned long long quirks;
        bool power_lost;
+       unsigned sideband_at_suspend:1;
        void (*plat_start)(struct usb_hcd *);
        int (*init_quirk)(struct usb_hcd *);
        int (*suspend_quirk)(struct usb_hcd *);