USB: adds comment on suspend callback

This patch adds comments on interface driver suspend callback
to emphasize that the failure return value is ignored by
USB core in system sleep context, so do not try to recover
device for this case and let resume/reset_resume callback
handle the suspend failure if needed.

Also kerneldoc for usb_suspend_both() is updated with the
fact.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 8 insertions, 3 deletions

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index d938b2b99e3..eb1d00a3543 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -1196,9 +1196,14 @@ done:
  *
  * This is the central routine for suspending USB devices.  It calls the
  * suspend methods for all the interface drivers in @udev and then calls
- * the suspend method for @udev itself.  If an error occurs at any stage,
- * all the interfaces which were suspended are resumed so that they remain
- * in the same state as the device.
+ * the suspend method for @udev itself.  When the routine is called in
+ * autosuspend, if an error occurs at any stage, all the interfaces
+ * which were suspended are resumed so that they remain in the same
+ * state as the device, but when called from system sleep, all error
+ * from suspend methods of interfaces and the non-root-hub device itself
+ * are simply ignored, so all suspended interfaces are only resumed
+ * to the device's state when @udev is root-hub and its suspend method
+ * returns failure.
  *
  * Autosuspend requests originating from a child device or an interface
  * driver may be made without the protection of @udev's device lock, but