usb: Make USB persist default configurable

Commit 9214d1d8 set the USB persist flag as a default for all devices.
This might be desirable for some distributions, but it certainly has its
trade-offs... most importantly, it can significantly increase system
resume time, because the kernel blocks on resuming (and sometimes
resetting) USB devices before it unfreezes userspace.

This patch introduces a new config option CONFIG_USB_DEFAULT_PERSIST,
which allows distributions to make this decision on their own without
the need to carry a custom patch or revert the kernel's setting in
userspace.

[edited the Kconfig help text a bit - gregkh]

Signed-off-by: Julius Werner <jwerner@chromium.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 21 insertions, 11 deletions

diff --git a/drivers/usb/core/Kconfig b/drivers/usb/core/Kconfig
index 175701a2dae4..7b7305e3abc8 100644
--- a/drivers/usb/core/Kconfig
+++ b/drivers/usb/core/Kconfig
@@ -27,6 +27,22 @@ config USB_ANNOUNCE_NEW_DEVICES
 comment "Miscellaneous USB options"
         depends on USB
 
+config USB_DEFAULT_PERSIST
+        bool "Enable USB persist by default"
+        depends on USB
+        default y
+        help
+          Say N here if you don't want USB power session persistance
+          enabled by default.  If you say N it will make suspended USB
+          devices that lose power get reenumerated as if they had been
+          unplugged, causing any mounted filesystems to be lost.  The
+          persist feature can still be enabled for individual devices
+          through the power/persist sysfs node. See
+          Documentation/usb/persist.txt for more info.
+
+          If you have any questions about this, say Y here, only say N
+          if you know exactly what you are doing.
+
 config USB_DYNAMIC_MINORS
         bool "Dynamic USB minor allocation"
         depends on USB
diff --git a/drivers/usb/core/quirks.c b/drivers/usb/core/quirks.c
index 3113c1d71442..ab5638d9c707 100644
--- a/drivers/usb/core/quirks.c
+++ b/drivers/usb/core/quirks.c
@@ -201,20 +201,14 @@ void usb_detect_quirks(struct usb_device *udev)
                 dev_dbg(&udev->dev, "USB quirks for this device: %x\n",
                         udev->quirks);
 
-        /* For the present, all devices default to USB-PERSIST enabled */
-#if 0           /* was: #ifdef CONFIG_PM */
-        /* Hubs are automatically enabled for USB-PERSIST */
-        if (udev->descriptor.bDeviceClass == USB_CLASS_HUB)
+#ifdef CONFIG_USB_DEFAULT_PERSIST
+        if (!(udev->quirks & USB_QUIRK_RESET))
                 udev->persist_enabled = 1;
-
 #else
-        /* In the absence of PM, we can safely enable USB-PERSIST
-         * for all devices.  It will affect things like hub resets
-         * and EMF-related port disables.
-         */
-        if (!(udev->quirks & USB_QUIRK_RESET))
+        /* Hubs are automatically enabled for USB-PERSIST */
+        if (udev->descriptor.bDeviceClass == USB_CLASS_HUB)
                 udev->persist_enabled = 1;
-#endif  /* CONFIG_PM */
+#endif  /* CONFIG_USB_DEFAULT_PERSIST */
 }
 
 void usb_detect_interface_quirks(struct usb_device *udev)