PM / core: Add NEVER_SKIP and SMART_PREPARE driver flags

The motivation for this change is to provide a way to work around
a problem with the direct-complete mechanism used for avoiding
system suspend/resume handling for devices in runtime suspend.

The problem is that some middle layer code (the PCI bus type and
the ACPI PM domain in particular) returns positive values from its
system suspend ->prepare callbacks regardless of whether the driver's
->prepare returns a positive value or 0, which effectively prevents
drivers from being able to control the direct-complete feature.
Some drivers need that control, however, and the PCI bus type has
grown its own flag to deal with this issue, but since it is not
limited to PCI, it is better to address it by adding driver flags at
the core level.

To that end, add a driver_flags field to struct dev_pm_info for flags
that can be set by device drivers at the probe time to inform the PM
core and/or bus types, PM domains and so on on the capabilities and/or
preferences of device drivers.  Also add two static inline helpers
for setting that field and testing it against a given set of flags
and make the driver core clear it automatically on driver remove
and probe failures.

Define and document two PM driver flags related to the direct-
complete feature: NEVER_SKIP and SMART_PREPARE that can be used,
respectively, to indicate to the PM core that the direct-complete
mechanism should never be used for the device and to inform the
middle layer code (bus types, PM domains etc) that it can only
request the PM core to use the direct-complete mechanism for
the device (by returning a positive value from its ->prepare
callback) if it also has been requested by the driver.

While at it, make the core check pm_runtime_suspended() when
setting power.direct_complete so that it doesn't need to be
checked by ->prepare callbacks.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

diff --git a/Documentation/driver-api/pm/devices.rst b/Documentation/driver-api/pm/devices.rst
index 4a18ef9997c0d00ca5ef96ac70a2e66be4acf360..8add5b302a89c0ebb7ee51865fa0b84bb4976dc7 100644 (file)
--- a/Documentation/driver-api/pm/devices.rst
+++ b/Documentation/driver-api/pm/devices.rst
@@ -354,6 +354,20 @@ the phases are: ``prepare``, ``suspend``, ``suspend_late``, ``suspend_noirq``.
        is because all such devices are initially set to runtime-suspended with
        runtime PM disabled.
 
+       This feature also can be controlled by device drivers by using the
+       ``DPM_FLAG_NEVER_SKIP`` and ``DPM_FLAG_SMART_PREPARE`` driver power
+       management flags.  [Typically, they are set at the time the driver is
+       probed against the device in question by passing them to the
+       :c:func:`dev_pm_set_driver_flags` helper function.]  If the first of
+       these flags is set, the PM core will not apply the direct-complete
+       procedure described above to the given device and, consequenty, to any
+       of its ancestors.  The second flag, when set, informs the middle layer
+       code (bus types, device types, PM domains, classes) that it should take
+       the return value of the ``->prepare`` callback provided by the driver
+       into account and it may only return a positive value from its own
+       ``->prepare`` callback if the driver's one also has returned a positive
+       value.
+
     2. The ``->suspend`` methods should quiesce the device to stop it from
        performing I/O.  They also may save the device registers and put it into
        the appropriate low-power state, depending on the bus type the device is

diff --git a/Documentation/power/pci.txt b/Documentation/power/pci.txt
index a1b7f715893050bc16a94b8ae63b50b9c51d3479..ab4e7d0540c15e3d7cdcdb7a20d1349a00f70228 100644 (file)
--- a/Documentation/power/pci.txt
+++ b/Documentation/power/pci.txt
@@ -961,6 +961,25 @@ dev_pm_ops to indicate that one suspend routine is to be pointed to by the
 .suspend(), .freeze(), and .poweroff() members and one resume routine is to
 be pointed to by the .resume(), .thaw(), and .restore() members.
 
+3.1.19. Driver Flags for Power Management
+
+The PM core allows device drivers to set flags that influence the handling of
+power management for the devices by the core itself and by middle layer code
+including the PCI bus type.  The flags should be set once at the driver probe
+time with the help of the dev_pm_set_driver_flags() function and they should not
+be updated directly afterwards.
+
+The DPM_FLAG_NEVER_SKIP flag prevents the PM core from using the direct-complete
+mechanism allowing device suspend/resume callbacks to be skipped if the device
+is in runtime suspend when the system suspend starts.  That also affects all of
+the ancestors of the device, so this flag should only be used if absolutely
+necessary.
+
+The DPM_FLAG_SMART_PREPARE flag instructs the PCI bus type to only return a
+positive value from pci_pm_prepare() if the ->prepare callback provided by the
+driver of the device returns a positive value.  That allows the driver to opt
+out from using the direct-complete mechanism dynamically.
+
 3.2. Device Runtime Power Management
 ------------------------------------
 In addition to providing device power management callbacks PCI device drivers

diff --git a/drivers/acpi/device_pm.c b/drivers/acpi/device_pm.c
index 17e8eb93a76c7e81fd86ff2d4077037d49599e5f..b4dcc6144e6bd974a82cdc59bb528e1395e98f68 100644 (file)
--- a/drivers/acpi/device_pm.c
+++ b/drivers/acpi/device_pm.c
@@ -959,11 +959,16 @@ static bool acpi_dev_needs_resume(struct device *dev, struct acpi_device *adev)
 int acpi_subsys_prepare(struct device *dev)
 {
        struct acpi_device *adev = ACPI_COMPANION(dev);
-       int ret;
 
-       ret = pm_generic_prepare(dev);
-       if (ret < 0)
-               return ret;
+       if (dev->driver && dev->driver->pm && dev->driver->pm->prepare) {
+               int ret = dev->driver->pm->prepare(dev);
+
+               if (ret < 0)
+                       return ret;
+
+               if (!ret && dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_PREPARE))
+                       return 0;
+       }
 
        if (!adev || !pm_runtime_suspended(dev))
                return 0;

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index ad44b40fe2847d219e50a5d51d799f2541b5d6d0..45575e134696280b4b2de4635b9631f1737b0f58 100644 (file)
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -464,6 +464,7 @@ pinctrl_bind_failed:
        if (dev->pm_domain && dev->pm_domain->dismiss)
                dev->pm_domain->dismiss(dev);
        pm_runtime_reinit(dev);
+       dev_pm_set_driver_flags(dev, 0);
 
        switch (ret) {
        case -EPROBE_DEFER:
@@ -869,6 +870,7 @@ static void __device_release_driver(struct device *dev, struct device *parent)
                if (dev->pm_domain && dev->pm_domain->dismiss)
                        dev->pm_domain->dismiss(dev);
                pm_runtime_reinit(dev);
+               dev_pm_set_driver_flags(dev, 0);
 
                klist_remove(&dev->p->knode_driver);
                device_pm_check_callbacks(dev);

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 9bbbbb13a9db81f2f1d1d364d7abbe058584ea4f..c0135cd95ada270f9185771d4c6d934d911388c0 100644 (file)
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -1700,7 +1700,9 @@ unlock:
         * applies to suspend transitions, however.
         */
        spin_lock_irq(&dev->power.lock);
-       dev->power.direct_complete = ret > 0 && state.event == PM_EVENT_SUSPEND;
+       dev->power.direct_complete = state.event == PM_EVENT_SUSPEND &&
+               pm_runtime_suspended(dev) && ret > 0 &&
+               !dev_pm_test_driver_flags(dev, DPM_FLAG_NEVER_SKIP);
        spin_unlock_irq(&dev->power.lock);
        return 0;
 }

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 11bd267fc1371acc303795876a6fba0b7725767a..68a32703b30a32ef1aa293097d2c481980bb0ecc 100644 (file)
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -689,8 +689,11 @@ static int pci_pm_prepare(struct device *dev)
 
        if (drv && drv->pm && drv->pm->prepare) {
                int error = drv->pm->prepare(dev);
-               if (error)
+               if (error < 0)
                        return error;
+
+               if (!error && dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_PREPARE))
+                       return 0;
        }
        return pci_dev_keep_suspended(to_pci_dev(dev));
 }

diff --git a/include/linux/device.h b/include/linux/device.h
index c32e6f974d4aabf6954598ade63860016bcbe041..fb9451599aca948082a7a194556a7f5272f05115 100644 (file)
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -1070,6 +1070,16 @@ static inline void dev_pm_syscore_device(struct device *dev, bool val)
 #endif
 }
 
+static inline void dev_pm_set_driver_flags(struct device *dev, u32 flags)
+{
+       dev->power.driver_flags = flags;
+}
+
+static inline bool dev_pm_test_driver_flags(struct device *dev, u32 flags)
+{
+       return !!(dev->power.driver_flags & flags);
+}
+
 static inline void device_lock(struct device *dev)
 {
        mutex_lock(&dev->mutex);

diff --git a/include/linux/pm.h b/include/linux/pm.h
index a0ceeccf284630933b6ca211e6860f510c9c3a5a..f10bad831bfa49ee0e9650f37a0f079b77bb052a 100644 (file)
--- a/include/linux/pm.h
+++ b/include/linux/pm.h
@@ -550,6 +550,25 @@ struct pm_subsys_data {
 #endif
 };
 
+/*
+ * Driver flags to control system suspend/resume behavior.
+ *
+ * These flags can be set by device drivers at the probe time.  They need not be
+ * cleared by the drivers as the driver core will take care of that.
+ *
+ * NEVER_SKIP: Do not skip system suspend/resume callbacks for the device.
+ * SMART_PREPARE: Check the return value of the driver's ->prepare callback.
+ *
+ * Setting SMART_PREPARE instructs bus types and PM domains which may want
+ * system suspend/resume callbacks to be skipped for the device to return 0 from
+ * their ->prepare callbacks if the driver's ->prepare callback returns 0 (in
+ * other words, the system suspend/resume callbacks can only be skipped for the
+ * device if its driver doesn't object against that).  This flag has no effect
+ * if NEVER_SKIP is set.
+ */
+#define DPM_FLAG_NEVER_SKIP    BIT(0)
+#define DPM_FLAG_SMART_PREPARE BIT(1)
+
 struct dev_pm_info {
        pm_message_t            power_state;
        unsigned int            can_wakeup:1;
@@ -561,6 +580,7 @@ struct dev_pm_info {
        bool                    is_late_suspended:1;
        bool                    early_init:1;   /* Owned by the PM core */
        bool                    direct_complete:1;      /* Owned by the PM core */
+       u32                     driver_flags;
        spinlock_t              lock;
 #ifdef CONFIG_PM_SLEEP
        struct list_head        entry;