On Fri, Mar 16, 2018 at 01:51:01PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>
> Introduce a driver for the ACPI Time and Alarm Device (TAD) based on
> Section 9.18 of ACPI 6.2.
Does UEFI bios for CNL support it already? Perhaps we can try this out and
share some feedback. Some minor styling related comments below.
>
> This driver only supports the system wakeup capabilities of the TAD
> which are mandatory. Support for the RTC capabilities of the TAD
I guess two whitespaces are put intentionally. IMO, even one looks as good
or better.
> will be added to it in the future.
>
> This driver is entirely sysfs-based. It provides attributes (under
Ditto
> the TAD platform device) to allow user space to manage the AC and DC
> wakeup timers of the TAD: set and read their values, set and check
> their expire timer wake policies, check and clear their status and
> check the capabilities of the TAD reported by AML. The DC timer
Ditto, and elsewhere too below.
> attributes are only present if the TAD supports a separate DC alarm
> timer.
>
> The wakeup events handling and power management of the TAD is
> expected to be taken care of by the ACPI PM domain attached to its
> platform device.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
> Documentation/ABI/testing/sysfs-devices-platform-ACPI-TAD | 113 +++
> drivers/acpi/Kconfig | 14
> drivers/acpi/Makefile | 1
> drivers/acpi/acpi_tad.c | 473 ++++++++++++++
> 4 files changed, 601 insertions(+)
Please update MAINTAINERS too.
>
> Index: linux-pm/drivers/acpi/Kconfig
> ===================================================================
> --- linux-pm.orig/drivers/acpi/Kconfig
> +++ linux-pm/drivers/acpi/Kconfig
> @@ -217,6 +217,20 @@ config ACPI_FAN
> To compile this driver as a module, choose M here:
> the module will be called fan.
>
> +config ACPI_TAD
> + tristate "ACPI Time and Alarm (TAD) Device Support"
> + depends on SYSFS && PM_SLEEP
> + default n
This may be removed.
> + help
> + The ACPI Time and Alarm (TAD) device is an alternative to the Real
> + Time Clock (RTC). Its wake timers allow the system to transition from
> + the S3 (or optionally S4/S5) state to S0 state after a time period
> + elapses. In comparison with the RTC Alarm, the TAD provides a larger
> + scale of flexibility in the wake timers. The time capabilities of the
> + TAD maintain the time of day information across platform power
> + transitions, and keep track of time even when the platform is turned
> + off.
> +
> config ACPI_DOCK
> bool "Dock"
> help
> Index: linux-pm/drivers/acpi/Makefile
> ===================================================================
> --- linux-pm.orig/drivers/acpi/Makefile
> +++ linux-pm/drivers/acpi/Makefile
> @@ -70,6 +70,7 @@ obj-$(CONFIG_ACPI_AC) += ac.o
> obj-$(CONFIG_ACPI_BUTTON) += button.o
> obj-$(CONFIG_ACPI_FAN) += fan.o
> obj-$(CONFIG_ACPI_VIDEO) += video.o
> +obj-$(CONFIG_ACPI_TAD) += acpi_tad.o
> obj-$(CONFIG_ACPI_PCI_SLOT) += pci_slot.o
> obj-$(CONFIG_ACPI_PROCESSOR) += processor.o
> obj-$(CONFIG_ACPI) += container.o
> Index: linux-pm/drivers/acpi/acpi_tad.c
> ===================================================================
> --- /dev/null
> +++ linux-pm/drivers/acpi/acpi_tad.c
> @@ -0,0 +1,473 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * ACPI Time and Alarm (TAD) Device Driver
> + *
> + * Copyright (C) 2018 Intel Corporation
> + * Author: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> + *
> + * This driver is based on Section 9.18 of the ACPI 6.2 specification revision.
> + *
> + * It only supports the system wakeup capabilities of the TAD.
> + *
> + * Provided are sysfs attributes, available under the TAD platform device,
> + * allowing user space to manage the AC and DC wakeup timers of the TAD:
> + * set and read their values, set and check their expire timer wake policies,
> + * check and clear their status and check the capabilities of the TAD reported
> + * by AML. The DC timer attributes are only present if the TAD supports a
> + * separate DC alarm timer.
> + *
> + * The wakeup events handling and power management of the TAD is expected to
> + * be taken care of by the ACPI PM domain attached to its platform device.
> + */
> +
> +#include <linux/acpi.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/suspend.h>
> +
> +MODULE_LICENSE("GPL v2");
> +MODULE_AUTHOR("Rafael J. Wysocki");
> +
> +/* ACPI TAD capability flags (ACPI 6.2, Section 9.18.2) */
> +#define ACPI_TAD_AC_WAKE BIT(0)
> +#define ACPI_TAD_DC_WAKE BIT(1)
> +#define ACPI_TAD_RT BIT(2)
> +#define ACPI_TAD_RT_IN_MS BIT(3)
> +#define ACPI_TAD_S4_S5__GWS BIT(4)
> +#define ACPI_TAD_AC_S4_WAKE BIT(5)
> +#define ACPI_TAD_AC_S5_WAKE BIT(6)
> +#define ACPI_TAD_DC_S4_WAKE BIT(7)
> +#define ACPI_TAD_DC_S5_WAKE BIT(8)
> +
> +/* ACPI TAD alarm timer selection */
> +#define ACPI_TAD_AC_TIMER (u32)0
> +#define ACPI_TAD_DC_TIMER (u32)1
> +
> +/* Special value for disabled timer or expired timer wake policy. */
> +#define ACPI_TAD_WAKE_DISABLED (~(u32)0)
> +
> +struct acpi_tad_driver_data {
> + u32 capabilities;
> +};
> +
> +static int acpi_tad_wake_set(struct device *dev, char *method, u32 timer_id,
> + u32 value)
> +{
> + acpi_handle handle = ACPI_HANDLE(dev);
> + union acpi_object args[] = {
> + { .type = ACPI_TYPE_INTEGER, },
> + { .type = ACPI_TYPE_INTEGER, },
> + };
> + struct acpi_object_list arg_list = {
> + .pointer = args,
> + .count = ARRAY_SIZE(args),
> + };
> + unsigned long long retval;
> + acpi_status status;
though its a matter of personal preference but these can be moved up and a
newline after struct closing brace.
> +
> + args[0].integer.value = timer_id;
> + args[1].integer.value = value;
> +
> + pm_runtime_get_sync(dev);
> +
> + status = acpi_evaluate_integer(handle, method, &arg_list, &retval);
> +
> + pm_runtime_put_sync(dev);
> +
> + if (ACPI_FAILURE(status) || retval)
> + return -EIO;
> +
> + return 0;
> +}
> +
> +static int acpi_tad_wake_write(struct device *dev, const char *buf, char *method,
Going abovbe 80.
> + u32 timer_id, const char *specval)
> +{
> + u32 value;
> +
> + if (sysfs_streq(buf, specval)) {
> + value = ACPI_TAD_WAKE_DISABLED;
> + } else {
> + int ret = kstrtou32(buf, 0, &value);
> +
> + if (ret)
> + return ret;
> +
> + if (value == ACPI_TAD_WAKE_DISABLED)
> + return -EINVAL;
> + }
> +
> + return acpi_tad_wake_set(dev, method, timer_id, value);
> +}
> +
> +static ssize_t acpi_tad_wake_read(struct device *dev, char *buf, char *method,
> + u32 timer_id, const char *specval)
> +{
> + acpi_handle handle = ACPI_HANDLE(dev);
> + union acpi_object args[] = {
> + { .type = ACPI_TYPE_INTEGER, },
> + };
> + struct acpi_object_list arg_list = {
> + .pointer = args,
> + .count = ARRAY_SIZE(args),
> + };
> + unsigned long long retval;
> + acpi_status status;
> +
> + args[0].integer.value = timer_id;
> +
> + pm_runtime_get_sync(dev);
> +
> + status = acpi_evaluate_integer(handle, method, &arg_list, &retval);
> +
> + pm_runtime_put_sync(dev);
> +
> + if (ACPI_FAILURE(status))
> + return -EIO;
> +
> + if ((u32)retval == ACPI_TAD_WAKE_DISABLED)
> + return sprintf(buf, "%s\n", specval);
> +
> + return sprintf(buf, "%u\n", (u32)retval);
> +}
> +
> +static const char *alarm_specval = "disabled";
> +
> +static int acpi_tad_alarm_write(struct device *dev, const char *buf,
> + u32 timer_id)
> +{
> + return acpi_tad_wake_write(dev, buf, "_STV", timer_id, alarm_specval);
> +}
> +
> +static ssize_t acpi_tad_alarm_read(struct device *dev, char *buf, u32 timer_id)
> +{
> + return acpi_tad_wake_read(dev, buf, "_TIV", timer_id, alarm_specval);
> +}
> +
> +static const char *policy_specval = "never";
> +
> +static int acpi_tad_policy_write(struct device *dev, const char *buf,
> + u32 timer_id)
> +{
> + return acpi_tad_wake_write(dev, buf, "_STP", timer_id, policy_specval);
> +}
> +
> +static ssize_t acpi_tad_policy_read(struct device *dev, char *buf, u32 timer_id)
> +{
> + return acpi_tad_wake_read(dev, buf, "_TIP", timer_id, policy_specval);
> +}
> +
> +static int acpi_tad_clear_status(struct device *dev, u32 timer_id)
> +{
> + acpi_handle handle = ACPI_HANDLE(dev);
> + union acpi_object args[] = {
> + { .type = ACPI_TYPE_INTEGER, },
> + };
> + struct acpi_object_list arg_list = {
> + .pointer = args,
> + .count = ARRAY_SIZE(args),
> + };
> + unsigned long long retval;
> + acpi_status status;
> +
> + args[0].integer.value = timer_id;
> +
> + pm_runtime_get_sync(dev);
> +
> + status = acpi_evaluate_integer(handle, "_CWS", &arg_list, &retval);
> +
> + pm_runtime_put_sync(dev);
> +
> + if (ACPI_FAILURE(status) || retval)
> + return -EIO;
> +
> + return 0;
> +}
> +
> +static int acpi_tad_status_write(struct device *dev, const char *buf, u32 timer_id)
> +{
> + int ret, value;
> +
> + ret = kstrtoint(buf, 0, &value);
> + if (ret)
> + return ret;
> +
> + if (value)
> + return -EINVAL;
> +
> + return acpi_tad_clear_status(dev, timer_id);
> +}
> +
> +static ssize_t acpi_tad_status_read(struct device *dev, char *buf, u32 timer_id)
> +{
> + acpi_handle handle = ACPI_HANDLE(dev);
> + union acpi_object args[] = {
> + { .type = ACPI_TYPE_INTEGER, },
> + };
> + struct acpi_object_list arg_list = {
> + .pointer = args,
> + .count = ARRAY_SIZE(args),
> + };
> + unsigned long long retval;
> + acpi_status status;
> +
> + args[0].integer.value = timer_id;
> +
> + pm_runtime_get_sync(dev);
> +
> + status = acpi_evaluate_integer(handle, "_GWS", &arg_list, &retval);
> +
> + pm_runtime_put_sync(dev);
> +
> + if (ACPI_FAILURE(status))
> + return -EIO;
> +
> + return sprintf(buf, "0x%02X\n", (u32)retval);
> +}
> +
> +static ssize_t caps_show(struct device *dev, struct device_attribute *attr,
> + char *buf)
> +{
> + struct acpi_tad_driver_data *dd = dev_get_drvdata(dev);
> +
> + return sprintf(buf, "0x%02X\n", dd->capabilities);
> +}
> +
> +static DEVICE_ATTR_RO(caps);
> +
> +static ssize_t ac_alarm_store(struct device *dev, struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + int ret = acpi_tad_alarm_write(dev, buf, ACPI_TAD_AC_TIMER);
> +
> + return ret ? ret : count;
> +}
> +
> +static ssize_t ac_alarm_show(struct device *dev, struct device_attribute *attr,
> + char *buf)
> +{
> + return acpi_tad_alarm_read(dev, buf, ACPI_TAD_AC_TIMER);
> +}
> +
> +static DEVICE_ATTR(ac_alarm, S_IRUSR | S_IWUSR, ac_alarm_show, ac_alarm_store);
> +
> +static ssize_t ac_policy_store(struct device *dev, struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + int ret = acpi_tad_policy_write(dev, buf, ACPI_TAD_AC_TIMER);
> +
> + return ret ? ret : count;
> +}
> +
> +static ssize_t ac_policy_show(struct device *dev, struct device_attribute *attr,
> + char *buf)
> +{
> + return acpi_tad_policy_read(dev, buf, ACPI_TAD_AC_TIMER);
> +}
> +
> +static DEVICE_ATTR(ac_policy, S_IRUSR | S_IWUSR, ac_policy_show, ac_policy_store);
> +
> +static ssize_t ac_status_store(struct device *dev, struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + int ret = acpi_tad_status_write(dev, buf, ACPI_TAD_AC_TIMER);
> +
> + return ret ? ret : count;
> +}
> +
> +static ssize_t ac_status_show(struct device *dev, struct device_attribute *attr,
> + char *buf)
> +{
> + return acpi_tad_status_read(dev, buf, ACPI_TAD_AC_TIMER);
> +}
> +
> +static DEVICE_ATTR(ac_status, S_IRUSR | S_IWUSR, ac_status_show, ac_status_store);
> +
> +static struct attribute *acpi_tad_attrs[] = {
> + &dev_attr_caps.attr,
> + &dev_attr_ac_alarm.attr,
> + &dev_attr_ac_policy.attr,
> + &dev_attr_ac_status.attr,
> + NULL,
> +};
> +static const struct attribute_group acpi_tad_attr_group = {
> + .attrs = acpi_tad_attrs,
> +};
> +
> +static ssize_t dc_alarm_store(struct device *dev, struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + int ret = acpi_tad_alarm_write(dev, buf, ACPI_TAD_DC_TIMER);
> +
> + return ret ? ret : count;
> +}
> +
> +static ssize_t dc_alarm_show(struct device *dev, struct device_attribute *attr,
> + char *buf)
> +{
> + return acpi_tad_alarm_read(dev, buf, ACPI_TAD_DC_TIMER);
> +}
> +
> +static DEVICE_ATTR(dc_alarm, S_IRUSR | S_IWUSR, dc_alarm_show, dc_alarm_store);
> +
> +static ssize_t dc_policy_store(struct device *dev, struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + int ret = acpi_tad_policy_write(dev, buf, ACPI_TAD_DC_TIMER);
> +
> + return ret ? ret : count;
> +}
> +
> +static ssize_t dc_policy_show(struct device *dev, struct device_attribute *attr,
> + char *buf)
> +{
> + return acpi_tad_policy_read(dev, buf, ACPI_TAD_DC_TIMER);
> +}
> +
> +static DEVICE_ATTR(dc_policy, S_IRUSR | S_IWUSR, dc_policy_show, dc_policy_store);
> +
> +static ssize_t dc_status_store(struct device *dev, struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + int ret = acpi_tad_status_write(dev, buf, ACPI_TAD_DC_TIMER);
> +
> + return ret ? ret : count;
> +}
> +
> +static ssize_t dc_status_show(struct device *dev, struct device_attribute *attr,
> + char *buf)
> +{
> + return acpi_tad_status_read(dev, buf, ACPI_TAD_DC_TIMER);
> +}
> +
> +static DEVICE_ATTR(dc_status, S_IRUSR | S_IWUSR, dc_status_show, dc_status_store);
> +
> +static struct attribute *acpi_tad_dc_attrs[] = {
> + &dev_attr_dc_alarm.attr,
> + &dev_attr_dc_policy.attr,
> + &dev_attr_dc_status.attr,
> + NULL,
> +};
Newline.
> +static const struct attribute_group acpi_tad_dc_attr_group = {
> + .attrs = acpi_tad_dc_attrs,
> +};
> +
> +static int acpi_tad_disable_timer(struct device *dev, u32 timer_id)
> +{
> + return acpi_tad_wake_set(dev, "_STV", timer_id, ACPI_TAD_WAKE_DISABLED);
> +}
> +
> +static int acpi_tad_remove(struct platform_device *pdev)
> +{
> + struct device *dev = &pdev->dev;
> + struct acpi_tad_driver_data *dd = dev_get_drvdata(dev);
> +
> + device_init_wakeup(dev, false);
> +
> + pm_runtime_get_sync(dev);
> +
> + if (dd->capabilities & ACPI_TAD_DC_WAKE)
> + sysfs_remove_group(&dev->kobj, &acpi_tad_dc_attr_group);
> +
> + sysfs_remove_group(&dev->kobj, &acpi_tad_attr_group);
> +
> + acpi_tad_disable_timer(dev, ACPI_TAD_AC_TIMER);
> + acpi_tad_clear_status(dev, ACPI_TAD_AC_TIMER);
> + if (dd->capabilities & ACPI_TAD_DC_WAKE) {
> + acpi_tad_disable_timer(dev, ACPI_TAD_DC_TIMER);
> + acpi_tad_clear_status(dev, ACPI_TAD_DC_TIMER);
> + }
> +
> + pm_runtime_put_sync(dev);
> + pm_runtime_disable(dev);
> + return 0;
> +}
> +
> +static int acpi_tad_probe(struct platform_device *pdev)
> +{
> + struct device *dev = &pdev->dev;
> + acpi_handle handle = ACPI_HANDLE(dev);
> + struct acpi_tad_driver_data *dd;
> + acpi_status status;
> + unsigned long long caps;
> + int ret;
> +
> + /*
> + * Initialization failure messages are mostly about firmware issues, so
> + * print them at the "info" level.
> + */
> + status = acpi_evaluate_integer(handle, "_GCP", NULL, &caps);
> + if (ACPI_FAILURE(status)) {
> + dev_info(dev, "Unable to get capabilities\n");
> + return -ENODEV;
> + }
> +
> + if (!(caps & ACPI_TAD_AC_WAKE)) {
> + dev_info(dev, "Unsupported capabilities\n");
> + return -ENODEV;
> + }
> +
> + if (!acpi_has_method(handle, "_PRW")) {
> + dev_info(dev, "Missing _PRW\n");
> + return -ENODEV;
> + }
> +
> + dd = devm_kzalloc(dev, sizeof(*dd), GFP_KERNEL);
> + if (!dd)
> + return -ENOMEM;
> +
> + dd->capabilities = caps;
> + dev_set_drvdata(dev, dd);
> +
> + /*
> + * Assume that the ACPI PM domain has been attached to the device and
> + * simply enable system wakeup and runtime PM and put the device into
> + * runtime suspend. Everything else should be taken care of by the ACPI
> + * PM domain callbacks.
> + */
> + device_init_wakeup(dev, true);
> + dev_pm_set_driver_flags(dev, DPM_FLAG_SMART_SUSPEND |
> + DPM_FLAG_LEAVE_SUSPENDED);
> + /*
> + * The platform bus type layer tells the ACPI PM domain powers up the
> + * device, so set the runtime PM status of it to "active".
> + */
> + pm_runtime_set_active(dev);
> + pm_runtime_enable(dev);
> + pm_runtime_suspend(dev);
> +
> + ret = sysfs_create_group(&dev->kobj, &acpi_tad_attr_group);
> + if (ret)
> + goto fail;
> +
> + if (caps & ACPI_TAD_DC_WAKE) {
> + ret = sysfs_create_group(&dev->kobj, &acpi_tad_dc_attr_group);
> + if (ret)
> + goto fail;
> + }
> +
> + return 0;
> +
> +fail:
> + acpi_tad_remove(pdev);
> + return ret;
> +}
> +
> +static const struct acpi_device_id acpi_tad_ids[] = {
> + {"ACPI000E", 0},
> + {}
> +};
> +
> +static struct platform_driver acpi_tad_driver = {
> + .driver = {
> + .name = "acpi-tad",
> + .acpi_match_table = acpi_tad_ids,
> + },
> + .probe = acpi_tad_probe,
> + .remove = acpi_tad_remove,
> +};
> +MODULE_DEVICE_TABLE(acpi, acpi_tad_ids);
> +
> +module_platform_driver(acpi_tad_driver);
> Index: linux-pm/Documentation/ABI/testing/sysfs-devices-platform-ACPI-TAD
> ===================================================================
> --- /dev/null
> +++ linux-pm/Documentation/ABI/testing/sysfs-devices-platform-ACPI-TAD
> @@ -0,0 +1,113 @@
> + ACPI Time and Alarm (TAD) device attributes.
> +
> +What: /sys/bus/platform/devices/ACPI000E:00/caps
> +Date: March 2018
> +Contact: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> +Description:
> + (RO) Hexadecimal bitmask of the TAD attributes are reported by
> + the platform firmware (see ACPI 6.2, section 9.18.2):
> +
> + BIT(0): AC wakeup implemented if set
> + BIT(1): DC wakeup implemented if set
> + BIT(2): Get/set real time features implemented if set
> + BIT(3): Real time accuracy in milliseconds if set
> + BIT(4): Correct status reported for wakeups from S4/S5 if set
> + BIT(5): The AC timer wakes up from S4 if set
> + BIT(6): The AC timer wakes up from S5 if set
> + BIT(7): The DC timer wakes up from S4 if set
> + BIT(8): The DC timer wakes up from S5 if set
> +
> + The other bits are reserved.
> +
> +What: /sys/bus/platform/devices/ACPI000E:00/ac_alarm
> +Date: March 2018
> +Contact: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> +Description:
> + (RW) The AC alarm timer value.
> +
> + Reads return the current AC alarm timer value in seconds or
> + "disabled", if the AC alarm is not set to wake up the system.
> +
> + Write a new AC alarm timer value in seconds or "disabled" to it
> + to set the AC alarm timer or to disable it, respectively.
> +
> + If the AC alarm timer is set through this attribute and it
> + expires, it will immediately wake up the system from the S3
> + sleep state (and from S4/S5 too if supported) until its status
> + is explicitly cleared via the ac_status attribute.
> +
> +What: /sys/bus/platform/devices/ACPI000E:00/ac_policy
> +Date: March 2018
> +Contact: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> +Description:
> + (RW) The AC alarm expired timer wake policy (see ACPI 6.2,
> + Section 9.18 for details).
> +
> + Reads return the current expired timer wake delay for the AC
> + alarm timer or "never", if the policy is to discard AC timer
> + wakeups if the system is on DC power.
> +
> + Write a new expired timer wake delay for the AC alarm timer in
> + seconds or "never" to it to set the expired timer wake delay for
> + the AC alarm timer or to set its expired wake policy to discard
> + wakeups if the system is on DC power, respectively.
> +
> +What: /sys/bus/platform/devices/ACPI000E:00/ac_status
> +Date: March 2018
> +Contact: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> +Description:
> + (RW) The AC alarm status.
> +
> + Reads return a hexadecimal bitmask representing the AC alarm
> + timer status with the following meaning of bits (see ACPI 6.2,
> + Section 9.18.5):
> +
> + Bit(0): The timer has expired if set.
> + Bit(1): The timer has woken up the system from a sleep state
> + (S3 or S4/S5 if supported) if set.
> +
> + The other bits are reserved.
> +
> + Reads also cause the AC alarm timer status to be reset.
> +
> + Another way to reset the the status of the AC alarm timer is to
> + write (the number) 0 to this file.
> +
> + If the status return value indicates that the timer has expired,
> + it will immediately wake up the system from the S3 sleep state
> + (and from S4/S5 too if supported) until its status is explicitly
> + cleared through this attribute.
> +
> +What: /sys/bus/platform/devices/ACPI000E:00/dc_alarm
> +Date: March 2018
> +Contact: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> +Description:
> + (RW,optional) The DC alarm timer value.
> +
> + This attribute is only present if the TAD supports a separate
> + DC timer.
> +
> + It is analogous to the ac_alarm attribute.
> +
> +What: /sys/bus/platform/devices/ACPI000E:00/dc_policy
> +Date: March 2018
> +Contact: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> +Description:
> + (RW,optional) The DC alarm expired timer wake policy.
> +
> + This attribute is only present if the TAD supports a separate
> + DC timer.
> +
> + It is analogous to the ac_policy attribute.
> +
> +What: /sys/bus/platform/devices/ACPI000E:00/dc_status
> +Date: March 2018
> +Contact: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> +
> +Description:
> + (RW,optional) The DC alarm status.
> +
> + This attribute is only present if the TAD supports a separate
> + DC timer.
> +
> + It is analogous to the ac_status attribute.
>
--
Best Regards,
Rajneesh
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