path: root/drivers/usb/core
diff options
authorDan Williams <dan.j.williams@intel.com>2014-05-20 18:09:36 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-05-27 17:25:37 -0700
commit7027df36e41836b11f01b0d30eee40c55df7d013 (patch)
tree569e9374988609c0d591b3de9c48fd8184498059 /drivers/usb/core
parent7e73be227b1510a2ba1391185be7cc357e2226ef (diff)
usb: resume child device when port is powered on
Unconditionally wake up the child device when the power session is recovered. This addresses the following scenarios: 1/ The device may need a reset on power-session loss, without this change port power-on recovery exposes khubd to scenarios that usb_port_resume() is set to handle. Prior to port power control the only time a power session would be lost is during dpm_suspend of the hub. In that scenario usb_port_resume() is guaranteed to be called prior to khubd running for that port. With this change we wakeup the child device as soon as possible (prior to khubd running again for this port). Although khubd has facilities to wake a child device it will only do so if the portstatus / portchange indicates a suspend state. In the case of port power control we are not coming from a hub-port-suspend state. This implementation simply uses pm_request_resume() to wake the device and relies on the port_dev->status_lock to prevent any collisions between khubd and usb_port_resume(). 2/ This mechanism rate limits port power toggling. The minimum port power on/off period is now gated by the child device suspend/resume latency. Empirically this mitigates devices downgrading their connection on perceived instability of the host connection. This ratelimiting is really only relevant to port power control testing, but it is a nice side effect of closing the above race. Namely, the race of khubd for the given port running while a usb_port_resume() event is pending. 3/ Going forward we are finding that power-session recovery requires warm-resets (http://marc.info/?t=138659232900003&r=1&w=2). This mechanism allows for warm-resets to be requested at the same point in the resume path for hub dpm_suspend power session losses, or port rpm_suspend power session losses. 4/ If the device *was* disconnected the only time we'll know for sure is after a failed resume, so it's necessary for usb_port_runtime_resume() to expedite a usb_port_resume() to clean up the removed device. The reasoning for this is "least surprise" for the user. Turning on a port means that hotplug detection is again enabled for the port, it is surprising that devices that were removed while the port was off are not disconnected until they are attempted to be used. As a user "why would I try to use a device I removed from the system?" 1, 2, and 4 are not a problem in the system dpm_resume() case because, although the power-session is lost, khubd is frozen until after device resume. For the rpm_resume() case pm_request_resume() is used to request re-validation of the device, and if it happens to collide with a khubd run we rely on the port_dev->status_lock to synchronize those operations. Besides testing, the primary scenario where this mechanism is expected to be triggered is when the user changes the port power policy (control/pm_qos_no_poweroff, or power/control). Each time power is enabled want to revalidate the child device, where the revalidation is handled by usb_port_resume(). Given that this arranges for port_dev->child to be de-referenced in usb_port_runtime_resume() we need to make sure not to collide with usb_disconnect() that frees the usb_device. To this end we hold the port active with the "child_usage" reference across the disconnect event. Subsequently, the need to access hub->child_usage_bits lead to the creation of hub_disconnect_children() to remove any ambiguity of which "hub" is being acted on in usb_disconnect() (prompted-by sharp eyes from Alan). Cc: Rafael J. Wysocki <rjw@rjwysocki.net> Acked-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/usb/core')
2 files changed, 37 insertions, 14 deletions
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 28f5bbae35e0..6346fb2acbd7 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2039,6 +2039,18 @@ static void hub_free_dev(struct usb_device *udev)
hcd->driver->free_dev(hcd, udev);
+static void hub_disconnect_children(struct usb_device *udev)
+ struct usb_hub *hub = usb_hub_to_struct_hub(udev);
+ int i;
+ /* Free up all the children before we remove this device */
+ for (i = 0; i < udev->maxchild; i++) {
+ if (hub->ports[i]->child)
+ usb_disconnect(&hub->ports[i]->child);
+ }
* usb_disconnect - disconnect a device (usbcore-internal)
* @pdev: pointer to device being disconnected
@@ -2057,9 +2069,10 @@ static void hub_free_dev(struct usb_device *udev)
void usb_disconnect(struct usb_device **pdev)
- struct usb_device *udev = *pdev;
- struct usb_hub *hub = usb_hub_to_struct_hub(udev);
- int i;
+ struct usb_port *port_dev = NULL;
+ struct usb_device *udev = *pdev;
+ struct usb_hub *hub;
+ int port1;
/* mark the device as inactive, so any further urb submissions for
* this device (and any of its children) will fail immediately.
@@ -2071,11 +2084,7 @@ void usb_disconnect(struct usb_device **pdev)
- /* Free up all the children before we remove this device */
- for (i = 0; i < udev->maxchild; i++) {
- if (hub->ports[i]->child)
- usb_disconnect(&hub->ports[i]->child);
- }
+ hub_disconnect_children(udev);
/* deallocate hcd/hardware state ... nuking all pending urbs and
* cleaning up all state associated with the current configuration
@@ -2086,15 +2095,19 @@ void usb_disconnect(struct usb_device **pdev)
if (udev->parent) {
- int port1 = udev->portnum;
- struct usb_hub *hub = usb_hub_to_struct_hub(udev->parent);
- struct usb_port *port_dev = hub->ports[port1 - 1];
+ port1 = udev->portnum;
+ hub = usb_hub_to_struct_hub(udev->parent);
+ port_dev = hub->ports[port1 - 1];
sysfs_remove_link(&udev->dev.kobj, "port");
sysfs_remove_link(&port_dev->dev.kobj, "device");
- if (test_and_clear_bit(port1, hub->child_usage_bits))
- pm_runtime_put(&port_dev->dev);
+ /*
+ * As usb_port_runtime_resume() de-references udev, make
+ * sure no resumes occur during removal
+ */
+ if (!test_and_set_bit(port1, hub->child_usage_bits))
+ pm_runtime_get_sync(&port_dev->dev);
@@ -2116,6 +2129,9 @@ void usb_disconnect(struct usb_device **pdev)
*pdev = NULL;
+ if (port_dev && test_and_clear_bit(port1, hub->child_usage_bits))
+ pm_runtime_put(&port_dev->dev);
diff --git a/drivers/usb/core/port.c b/drivers/usb/core/port.c
index 8b1655700104..62036faf56c0 100644
--- a/drivers/usb/core/port.c
+++ b/drivers/usb/core/port.c
@@ -76,6 +76,7 @@ static int usb_port_runtime_resume(struct device *dev)
struct usb_device *hdev = to_usb_device(dev->parent->parent);
struct usb_interface *intf = to_usb_interface(dev->parent);
struct usb_hub *hub = usb_hub_to_struct_hub(hdev);
+ struct usb_device *udev = port_dev->child;
struct usb_port *peer = port_dev->peer;
int port1 = port_dev->portnum;
int retval;
@@ -97,7 +98,7 @@ static int usb_port_runtime_resume(struct device *dev)
retval = usb_hub_set_port_power(hdev, hub, port1, true);
- if (port_dev->child && !retval) {
+ if (udev && !retval) {
* Attempt to wait for usb hub port to be reconnected in order
* to make the resume procedure successful. The device may have
@@ -109,6 +110,12 @@ static int usb_port_runtime_resume(struct device *dev)
dev_dbg(&port_dev->dev, "can't get reconnection after setting port power on, status %d\n",
retval = 0;
+ /* Force the child awake to revalidate after the power loss. */
+ if (!test_and_set_bit(port1, hub->child_usage_bits)) {
+ pm_runtime_get_noresume(&port_dev->dev);
+ pm_request_resume(&udev->dev);
+ }