powerpc/pseries: Expose in kernel device tree update to drmgr

Traditionally it has been drmgr's responsibilty to update the device tree
through the /proc/ppc64/ofdt interface after a suspend/resume operation.
This patchset however has modified suspend/resume ops to preform an update
entirely in the kernel during the resume. Therefore, a mechanism is required
to expose that information to drmgr.

This patch adds a show function to the "hibernate" attribute that returns 1
if the kernel performs a device tree update after the resume and 0 otherwise.
This allows newer versions of drmgr to avoid doing a second unnecessary
device tree update.

Signed-off-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/pseries/suspend.c

@@ -192,7 +192,30 @@ static ssize_t store_hibernate(struct device *dev,
 	return rc;
 }
 
-static DEVICE_ATTR(hibernate, S_IWUSR, NULL, store_hibernate);
+#define USER_DT_UPDATE	0
+#define KERN_DT_UPDATE	1
+
+/**
+ * show_hibernate - Report device tree update responsibilty
+ * @dev:		subsys root device
+ * @attr:		device attribute struct
+ * @buf:		buffer
+ *
+ * Report whether a device tree update is performed by the kernel after a
+ * resume, or if drmgr must coordinate the update from user space.
+ *
+ * Return value:
+ *	0 if drmgr is to initiate update, and 1 otherwise
+ **/
+static ssize_t show_hibernate(struct device *dev,
+			      struct device_attribute *attr,
+			      char *buf)
+{
+	return sprintf(buf, "%d\n", KERN_DT_UPDATE);
+}
+
+static DEVICE_ATTR(hibernate, S_IWUSR | S_IRUGO,
+		   show_hibernate, store_hibernate);
 
 static struct bus_type suspend_subsys = {
 	.name = "power",