nfit/ars: Allow root to busy-poll the ARS state machine

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.

Fixes: bc6ba8085842 ("nfit, address-range-scrub: rework and simplify ARS...")
Cc: <stable@vger.kernel.org>
Reported-by: Erwin Tsaur <erwin.tsaur@oracle.com>
Reviewed-by: Toshi Kani <toshi.kani@hpe.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

2 files changed, 9 insertions, 0 deletions

diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
index 90312892093e..629cf91649d2 100644
--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -1333,6 +1333,13 @@ static ssize_t scrub_show(struct device *dev,
         busy = test_bit(ARS_BUSY, &acpi_desc->scrub_flags)
                 && !test_bit(ARS_CANCEL, &acpi_desc->scrub_flags);
         rc = sprintf(buf, "%d%s", acpi_desc->scrub_count, busy ? "+\n" : "\n");
+        /* Allow an admin to poll the busy state at a higher rate */
+        if (busy && capable(CAP_SYS_RAWIO) && !test_and_set_bit(ARS_POLL,
+                                &acpi_desc->scrub_flags)) {
+                acpi_desc->scrub_tmo = 1;
+                mod_delayed_work(nfit_wq, &acpi_desc->dwork, HZ);
+        }
+
         mutex_unlock(&acpi_desc->init_mutex);
         device_unlock(dev);
         return rc;
@@ -3187,6 +3194,7 @@ static void acpi_nfit_scrub(struct work_struct *work)
         else
                 notify_ars_done(acpi_desc);
         memset(acpi_desc->ars_status, 0, acpi_desc->max_ars);
+        clear_bit(ARS_POLL, &acpi_desc->scrub_flags);
         mutex_unlock(&acpi_desc->init_mutex);
 }
 
diff --git a/drivers/acpi/nfit/nfit.h b/drivers/acpi/nfit/nfit.h
index 897ce10192a0..d14bad687fb8 100644
--- a/drivers/acpi/nfit/nfit.h
+++ b/drivers/acpi/nfit/nfit.h
@@ -213,6 +213,7 @@ struct nfit_mem {
 enum scrub_flags {
         ARS_BUSY,
         ARS_CANCEL,
+        ARS_POLL,
 };
 
 struct acpi_nfit_desc {