path: root/drivers/usb/core/hub.c
diff options
authorSarah Sharp <sarah.a.sharp@linux.intel.com>2012-01-06 15:48:30 -0800
committerSarah Sharp <sarah.a.sharp@linux.intel.com>2012-02-14 12:12:23 -0800
commit3b9b6acd4798aafe9b9f64ccb7e8eb76f27f904a (patch)
treeeed2db913bdb2c1cd465a857b6175e9e3c4cbf55 /drivers/usb/core/hub.c
parent623bef9e03a60adc623b09673297ca7a1cdfb367 (diff)
USB: Suspend functions before putting dev into U3.
The USB 3.0 bus specification introduces a new type of power management called function suspend. The idea is to be able to suspend different functions (i.e. a scanner or an SD card reader on a USB printer) independently. A device can be in U0, but have one or more functions suspended. Thus, signaling a function resume with the standard device remote wake signaling was not possible. Instead, a device will (without prompt from the host) send a "device notification" for the function remote wake. A new Set Feature Function Remote Wake was developed to turn remote wake up on and off for each function. USB 3.0 devices can still go into device suspend (U3), and signal a remote wakeup to bring the link back into U1. However, they now use the function remote wake device notification to allow the host to know which function woke the device from U3. The spec is a bit ambiguous about whether a function is allowed to signal a remote wakeup if the function has been enabled for remote wakeup, but not placed in function suspend before the device is placed into U3. Section says "Suspending a device with more than one function effectively suspends all the functions within the device." I interpret that to mean that putting a device in U3 suspends all functions, and thus if the host has previously enabled remote wake for those functions, it should be able to signal a remote wake up on port status changes. However, hub vendors may have a different interpretation, and it can't hurt to put the function into suspend before putting the device into U3. I cannot get an answer out of the USB 3.0 spec architects about this ambiguity, so I'm erring on the safe side and always suspending the first function before placing the device in U3. Note, this code should be fixed if we ever find any USB 3.0 devices that have more than one function. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Diffstat (limited to 'drivers/usb/core/hub.c')
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 50411cd0ac4..70622d633fd 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2437,7 +2437,8 @@ int usb_port_suspend(struct usb_device *udev, pm_message_t msg)
NULL, 0,