[PATCH v2] nfit/ars: Allow root to busy-poll the ARS state machine

[Dan Williams]

The ARS implementation implements exponential back-off on the poll
interval to prevent high-frequency access to the DIMM / platform
interface. Depending on when the ARS completes the poll interval may
exceed the completion event by minutes. Allow root to reset the timeout
each time it probes the status. A one-second timeout is still enforced,
but root can otherwise can control the poll interval.

Reported-by: Erwin Tsaur <erwin.tsaur@xxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
Change since v1: Use mod_delayed_work() instead of queue_delayed_work()
to modify the timeout for existing work.

 drivers/acpi/nfit/core.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
index 934be96dc149..b1ab593a808a 100644
--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -1328,6 +1328,12 @@ static ssize_t scrub_show(struct device *dev,
 		rc = sprintf(buf, "%d%s", acpi_desc->scrub_count,
 				acpi_desc->scrub_busy
 				&& !acpi_desc->cancel ? "+\n" : "\n");
+		/* Allow an admin to poll the busy state at a higher rate */
+		if (acpi_desc->scrub_busy && !acpi_desc->cancel
+				&& capable(CAP_SYS_RAWIO)) {
+			acpi_desc->scrub_tmo = 1;
+			mod_delayed_work(nfit_wq, &acpi_desc->dwork, HZ);
+		}
 		mutex_unlock(&acpi_desc->init_mutex);
 	}
 	device_unlock(dev);