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Date: Fri, 4 Dec 2020 17:21:25 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Linux ACPI <linux-acpi@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Linux PM <linux-pm@...r.kernel.org>,
Linux PCI <linux-pci@...r.kernel.org>,
Mika Westerberg <mika.westerberg@...ux.intel.com>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Kai-Heng Feng <kai.heng.feng@...onical.com>
Subject: Re: [PATCH v1 1/2] PM: ACPI: PCI: Drop acpi_pm_set_bridge_wakeup()
On Tue, Nov 24, 2020 at 08:44:00PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> The idea behind acpi_pm_set_bridge_wakeup() was to allow bridges to
> be reference counted for wakeup enabling, because they may be enabled
> to signal wakeup on behalf of their subordinate devices and that
> may happen for multiple times in a row, whereas for the other devices
> it only makes sense to enable wakeup signaling once.
>
> However, this becomes problematic if the bridge itself is suspended,
> because it is treated as a "regular" device in that case and the
> reference counting doesn't work.
>
> For instance, suppose that there are two devices below a bridge and
> they both can signal wakeup. Every time one of them is suspended,
> wakeup signaling is enabled for the bridge, so when they both have
> been suspended, the bridge's wakeup reference counter value is 2.
>
> Say that the bridge is suspended subsequently and acpi_pci_wakeup()
> is called for it. Because the bridge can signal wakeup, that
> function will invoke acpi_pm_set_device_wakeup() to configure it
> and __acpi_pm_set_device_wakeup() will be called with the last
> argument equal to 1. This causes __acpi_device_wakeup_enable()
> invoked by it to omit the reference counting, because the reference
> counter of the target device (the bridge) is 2 at that time.
>
> Now say that the bridge resumes and one of the device below it
> resumes too, so the bridge's reference counter becomes 0 and
> wakeup signaling is disabled for it, but there is still the other
> suspended device which may need the bridge to signal wakeup on its
> behalf and that is not going to work.
>
> To address this scenario, use wakeup enable reference counting for
> all devices, not just for bridges, so drop the last argument from
> __acpi_device_wakeup_enable() and __acpi_pm_set_device_wakeup(),
> which causes acpi_pm_set_device_wakeup() and
> acpi_pm_set_bridge_wakeup() to become identical, so drop the latter
> and use the former instead of it everywhere.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
> drivers/acpi/device_pm.c | 41 ++++++++++++-----------------------------
> drivers/pci/pci-acpi.c | 4 ++--
> include/acpi/acpi_bus.h | 5 -----
> 3 files changed, 14 insertions(+), 36 deletions(-)
>
> Index: linux-pm/include/acpi/acpi_bus.h
> ===================================================================
> --- linux-pm.orig/include/acpi/acpi_bus.h
> +++ linux-pm/include/acpi/acpi_bus.h
> @@ -620,7 +620,6 @@ acpi_status acpi_remove_pm_notifier(stru
> bool acpi_pm_device_can_wakeup(struct device *dev);
> int acpi_pm_device_sleep_state(struct device *, int *, int);
> int acpi_pm_set_device_wakeup(struct device *dev, bool enable);
> -int acpi_pm_set_bridge_wakeup(struct device *dev, bool enable);
> #else
> static inline void acpi_pm_wakeup_event(struct device *dev)
> {
> @@ -651,10 +650,6 @@ static inline int acpi_pm_set_device_wak
> {
> return -ENODEV;
> }
> -static inline int acpi_pm_set_bridge_wakeup(struct device *dev, bool enable)
> -{
> - return -ENODEV;
> -}
> #endif
>
> #ifdef CONFIG_ACPI_SYSTEM_POWER_STATES_SUPPORT
> Index: linux-pm/drivers/acpi/device_pm.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/device_pm.c
> +++ linux-pm/drivers/acpi/device_pm.c
> @@ -749,7 +749,7 @@ static void acpi_pm_notify_work_func(str
> static DEFINE_MUTEX(acpi_wakeup_lock);
>
> static int __acpi_device_wakeup_enable(struct acpi_device *adev,
> - u32 target_state, int max_count)
> + u32 target_state)
> {
> struct acpi_device_wakeup *wakeup = &adev->wakeup;
> acpi_status status;
> @@ -757,9 +757,10 @@ static int __acpi_device_wakeup_enable(s
>
> mutex_lock(&acpi_wakeup_lock);
>
> - if (wakeup->enable_count >= max_count)
> + if (wakeup->enable_count >= INT_MAX) {
> + acpi_handle_info(adev->handle, "Wakeup enable count out of bounds!\n");
> goto out;
> -
> + }
> if (wakeup->enable_count > 0)
> goto inc;
>
> @@ -799,7 +800,7 @@ out:
> */
> static int acpi_device_wakeup_enable(struct acpi_device *adev, u32 target_state)
> {
> - return __acpi_device_wakeup_enable(adev, target_state, 1);
> + return __acpi_device_wakeup_enable(adev, target_state);
> }
>
> /**
> @@ -829,8 +830,12 @@ out:
> mutex_unlock(&acpi_wakeup_lock);
> }
>
> -static int __acpi_pm_set_device_wakeup(struct device *dev, bool enable,
> - int max_count)
> +/**
> + * acpi_pm_set_device_wakeup - Enable/disable remote wakeup for given device.
> + * @dev: Device to enable/disable to generate wakeup events.
> + * @enable: Whether to enable or disable the wakeup functionality.
> + */
> +int acpi_pm_set_device_wakeup(struct device *dev, bool enable)
> {
> struct acpi_device *adev;
> int error;
> @@ -850,37 +855,15 @@ static int __acpi_pm_set_device_wakeup(s
> return 0;
> }
>
> - error = __acpi_device_wakeup_enable(adev, acpi_target_system_state(),
> - max_count);
> + error = __acpi_device_wakeup_enable(adev, acpi_target_system_state());
> if (!error)
> dev_dbg(dev, "Wakeup enabled by ACPI\n");
>
> return error;
> }
> -
> -/**
> - * acpi_pm_set_device_wakeup - Enable/disable remote wakeup for given device.
> - * @dev: Device to enable/disable to generate wakeup events.
> - * @enable: Whether to enable or disable the wakeup functionality.
> - */
> -int acpi_pm_set_device_wakeup(struct device *dev, bool enable)
> -{
> - return __acpi_pm_set_device_wakeup(dev, enable, 1);
> -}
> EXPORT_SYMBOL_GPL(acpi_pm_set_device_wakeup);
>
> /**
> - * acpi_pm_set_bridge_wakeup - Enable/disable remote wakeup for given bridge.
> - * @dev: Bridge device to enable/disable to generate wakeup events.
> - * @enable: Whether to enable or disable the wakeup functionality.
> - */
> -int acpi_pm_set_bridge_wakeup(struct device *dev, bool enable)
> -{
> - return __acpi_pm_set_device_wakeup(dev, enable, INT_MAX);
> -}
> -EXPORT_SYMBOL_GPL(acpi_pm_set_bridge_wakeup);
> -
> -/**
> * acpi_dev_pm_low_power - Put ACPI device into a low-power state.
> * @dev: Device to put into a low-power state.
> * @adev: ACPI device node corresponding to @dev.
> Index: linux-pm/drivers/pci/pci-acpi.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci-acpi.c
> +++ linux-pm/drivers/pci/pci-acpi.c
> @@ -1060,7 +1060,7 @@ static int acpi_pci_propagate_wakeup(str
> {
> while (bus->parent) {
> if (acpi_pm_device_can_wakeup(&bus->self->dev))
> - return acpi_pm_set_bridge_wakeup(&bus->self->dev, enable);
> + return acpi_pm_set_device_wakeup(&bus->self->dev, enable);
>
> bus = bus->parent;
> }
> @@ -1068,7 +1068,7 @@ static int acpi_pci_propagate_wakeup(str
> /* We have reached the root bus. */
> if (bus->bridge) {
> if (acpi_pm_device_can_wakeup(bus->bridge))
> - return acpi_pm_set_bridge_wakeup(bus->bridge, enable);
> + return acpi_pm_set_device_wakeup(bus->bridge, enable);
> }
> return 0;
> }
>
>
>
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