acpi, nfit: limit ->flush_probe() to initialization work

The nvdimm probe flushing mechanism gives userspace a sync point where
it knows all asynchronous driver probe sequences have completed.
However, it need not wait for other asynchronous actions, like
on-demand address-range-scrub. Track the init work separately from other
work in the workqueue, and only flush the former.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

drivers/acpi/nfit/core.c

@@ -2581,6 +2581,7 @@ static void acpi_nfit_scrub(struct work_struct *work)
 			acpi_nfit_register_region(acpi_desc, nfit_spa);
 		}
 	}
+	acpi_desc->init_complete = 1;
 
 	list_for_each_entry(nfit_spa, &acpi_desc->spas, list)
 		acpi_nfit_async_scrub(acpi_desc, nfit_spa);
@@ -2784,6 +2785,12 @@ static int acpi_nfit_flush_probe(struct nvdimm_bus_descriptor *nd_desc)
 	device_lock(dev);
 	device_unlock(dev);
 
+	/* bounce the init_mutex to make init_complete valid */
+	mutex_lock(&acpi_desc->init_mutex);
+	mutex_unlock(&acpi_desc->init_mutex);
+	if (acpi_desc->init_complete)
+		return 0;
+
 	/*
 	 * Scrub work could take 10s of seconds, userspace may give up so we
 	 * need to be interruptible while waiting.

drivers/acpi/nfit/nfit.h

@@ -163,6 +163,7 @@ struct acpi_nfit_desc {
 	unsigned int scrub_count;
 	unsigned int scrub_mode;
 	unsigned int cancel:1;
+	unsigned int init_complete:1;
 	unsigned long dimm_cmd_force_en;
 	unsigned long bus_cmd_force_en;
 	int (*blk_do_io)(struct nd_blk_region *ndbr, resource_size_t dpa,