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Subject[PATCH v2 5/6] nfit/ars: Allow root to busy-poll the ARS state machine
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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@oracle.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/acpi/nfit/core.c | 8 ++++++++
drivers/acpi/nfit/nfit.h | 1 +
2 files changed, 9 insertions(+)

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 {
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