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Subject[PATCH v2 1/2] ACPI / EC: Add PM operations to tune polling mode efficiency
Date
It is reported that on some platforms, resume speed is not fast. The cause
is: in noirq stage, EC driver is working in polling mode, and each state
machine advancement requires a context switch.

The context switch is not necessary to the EC driver's polling mode. This
patch implements PM hooks to automatically switch the driver to/from the
busy polling mode to eliminate the overhead caused by the context switch.

This finally contributes to the tuning result: acpi_pm_finish() execution
time is improved from 192ms to 6ms.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Reported-and-tested-by: Todd E Brandt <todd.e.brandt@linux.intel.com>
---
drivers/acpi/ec.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++
drivers/acpi/internal.h | 2 ++
2 files changed, 55 insertions(+)

diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
index 907b450..7cdcdf6 100644
--- a/drivers/acpi/ec.c
+++ b/drivers/acpi/ec.c
@@ -1619,6 +1619,58 @@ error:
return ret;
}

+#ifdef CONFIG_PM_SLEEP
+static void acpi_ec_enter_noirq(struct acpi_ec *ec)
+{
+ unsigned long flags;
+
+ if (ec == first_ec) {
+ spin_lock_irqsave(&ec->lock, flags);
+ ec->saved_busy_polling = ec_busy_polling;
+ ec->saved_polling_guard = ec_polling_guard;
+ ec_busy_polling = true;
+ ec_polling_guard = 0;
+ ec_log_drv("interrupt blocked");
+ spin_unlock_irqrestore(&ec->lock, flags);
+ }
+}
+
+static void acpi_ec_leave_noirq(struct acpi_ec *ec)
+{
+ unsigned long flags;
+
+ if (ec == first_ec) {
+ spin_lock_irqsave(&ec->lock, flags);
+ ec_busy_polling = ec->saved_busy_polling;
+ ec_polling_guard = ec->saved_polling_guard;
+ ec_log_drv("interrupt unblocked");
+ spin_unlock_irqrestore(&ec->lock, flags);
+ }
+}
+
+static int acpi_ec_suspend_noirq(struct device *dev)
+{
+ struct acpi_ec *ec =
+ acpi_driver_data(to_acpi_device(dev));
+
+ acpi_ec_enter_noirq(ec);
+ return 0;
+}
+
+static int acpi_ec_resume_noirq(struct device *dev)
+{
+ struct acpi_ec *ec =
+ acpi_driver_data(to_acpi_device(dev));
+
+ acpi_ec_leave_noirq(ec);
+ return 0;
+}
+#endif
+
+static const struct dev_pm_ops acpi_ec_pm = {
+ SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(acpi_ec_suspend_noirq, acpi_ec_resume_noirq)
+};
+
static int param_set_event_clearing(const char *val, struct kernel_param *kp)
{
int result = 0;
@@ -1664,6 +1716,7 @@ static struct acpi_driver acpi_ec_driver = {
.add = acpi_ec_add,
.remove = acpi_ec_remove,
},
+ .drv.pm = &acpi_ec_pm,
};

int __init acpi_ec_init(void)
diff --git a/drivers/acpi/internal.h b/drivers/acpi/internal.h
index 940218f..6996121 100644
--- a/drivers/acpi/internal.h
+++ b/drivers/acpi/internal.h
@@ -174,6 +174,8 @@ struct acpi_ec {
struct work_struct work;
unsigned long timestamp;
unsigned long nr_pending_queries;
+ bool saved_busy_polling;
+ unsigned int saved_polling_guard;
};

extern struct acpi_ec *first_ec;
--
1.7.10
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