[PATCH 3/6] 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.ts...@oracle.com>
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
---
 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..5ec0e19760ea 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;
+                       queue_delayed_work(nfit_wq, &acpi_desc->dwork, HZ);
+               }
                mutex_unlock(&acpi_desc->init_mutex);
        }
        device_unlock(dev);