ACPI/PM: specify lowest allowed state for device sleep state

Lower device sleep state can save more power, but has more exit
latency too.  Sometimes, to satisfy some power QoS and other
requirement, we need to constrain the lowest device sleep state.

In this patch, a parameter to specify lowest allowed state for
acpi_pm_device_sleep_state is added.  So that the caller can enforce
the constraint via the parameter.

This is needed by PCIe D3cold support, where the lowest power state
allowed may be D3_HOT instead of default D3_COLD.

CC: Len Brown <lenb@kernel.org>
CC: linux-acpi@vger.kernel.org
Reviewed-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

1 files changed, 19 insertions, 5 deletions

diff --git a/drivers/acpi/sleep.c b/drivers/acpi/sleep.c
index 88561029cca8..1cc02ca2af2a 100644
--- a/drivers/acpi/sleep.c
+++ b/drivers/acpi/sleep.c
@@ -716,8 +716,9 @@ int acpi_suspend(u32 acpi_state)
  *	@dev: device to examine; its driver model wakeup flags control
  *		whether it should be able to wake up the system
  *	@d_min_p: used to store the upper limit of allowed states range
- *	Return value: preferred power state of the device on success, -ENODEV on
- *		failure (ie. if there's no 'struct acpi_device' for @dev)
+ *	@d_max_in: specify the lowest allowed states
+ *	Return value: preferred power state of the device on success, -ENODEV
+ *	(ie. if there's no 'struct acpi_device' for @dev) or -EINVAL on failure
  *
  *	Find the lowest power (highest number) ACPI device power state that
  *	device @dev can be in while the system is in the sleep state represented
@@ -732,13 +733,15 @@ int acpi_suspend(u32 acpi_state)
  *	via @wake.
  */
 
-int acpi_pm_device_sleep_state(struct device *dev, int *d_min_p)
+int acpi_pm_device_sleep_state(struct device *dev, int *d_min_p, int d_max_in)
 {
 	acpi_handle handle = DEVICE_ACPI_HANDLE(dev);
 	struct acpi_device *adev;
 	char acpi_method[] = "_SxD";
 	unsigned long long d_min, d_max;
 
+	if (d_max_in < ACPI_STATE_D0 || d_max_in > ACPI_STATE_D3)
+		return -EINVAL;
 	if (!handle || ACPI_FAILURE(acpi_bus_get_device(handle, &adev))) {
 		printk(KERN_DEBUG "ACPI handle has no context!\n");
 		return -ENODEV;
@@ -746,8 +749,10 @@ int acpi_pm_device_sleep_state(struct device *dev, int *d_min_p)
 
 	acpi_method[2] = '0' + acpi_target_sleep_state;
 	/*
-	 * If the sleep state is S0, we will return D3, but if the device has
-	 * _S0W, we will use the value from _S0W
+	 * If the sleep state is S0, the lowest limit from ACPI is D3,
+	 * but if the device has _S0W, we will use the value from _S0W
+	 * as the lowest limit from ACPI.  Finally, we will constrain
+	 * the lowest limit with the specified one.
 	 */
 	d_min = ACPI_STATE_D0;
 	d_max = ACPI_STATE_D3;
@@ -791,8 +796,17 @@ int acpi_pm_device_sleep_state(struct device *dev, int *d_min_p)
 		}
 	}
 
+	if (d_max_in < d_min)
+		return -EINVAL;
 	if (d_min_p)
 		*d_min_p = d_min;
+	/* constrain d_max with specified lowest limit (max number) */
+	if (d_max > d_max_in) {
+		for (d_max = d_max_in; d_max > d_min; d_max--) {
+			if (adev->power.states[d_max].flags.valid)
+				break;
+		}
+	}
 	return d_max;
 }
 #endif /* CONFIG_PM */