From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751609AbdJWQhq (ORCPT ); Mon, 23 Oct 2017 12:37:46 -0400 Received: from mail-io0-f174.google.com ([209.85.223.174]:43676 "EHLO mail-io0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751429AbdJWQhn (ORCPT ); Mon, 23 Oct 2017 12:37:43 -0400 X-Google-Smtp-Source: ABhQp+SoI5/aEf0j1/CA6vufE/6hnLLpG+hS5247SQ7EE74v/pewZf7iAfdbe0PYrCnheOWDPdUsgVHxcU6TbqqlkLk= MIME-Version: 1.0 In-Reply-To: <11013815.Nxk07oyMGD@aspire.rjw.lan> References: <3806130.B2KCK0tvef@aspire.rjw.lan> <1998650.Q52BuGQTI4@aspire.rjw.lan> <11013815.Nxk07oyMGD@aspire.rjw.lan> From: Ulf Hansson Date: Mon, 23 Oct 2017 18:37:41 +0200 Message-ID: Subject: Re: [Update][PATCH v2 01/12] PM / core: Add NEVER_SKIP and SMART_PREPARE driver flags To: "Rafael J. Wysocki" Cc: Linux PM , Greg Kroah-Hartman , Lukas Wunner , Bjorn Helgaas , Alan Stern , LKML , Linux ACPI , Linux PCI , Linux Documentation , Mika Westerberg , Andy Shevchenko , Kevin Hilman , Wolfram Sang , "linux-i2c@vger.kernel.org" , Lee Jones Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19 October 2017 at 01:17, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki > > 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 > --- > > -> v2: Change the data type for driver_flags to u32 as suggested by Greg > and fix a couple of documentation typos pointed out by Lukas. > > --- > Documentation/driver-api/pm/devices.rst | 14 ++++++++++++++ > Documentation/power/pci.txt | 19 +++++++++++++++++++ > drivers/acpi/device_pm.c | 3 +++ > drivers/base/dd.c | 2 ++ > drivers/base/power/main.c | 4 +++- > drivers/pci/pci-driver.c | 5 ++++- > include/linux/device.h | 10 ++++++++++ > include/linux/pm.h | 20 ++++++++++++++++++++ > 8 files changed, 75 insertions(+), 2 deletions(-) > > Index: linux-pm/include/linux/device.h > =================================================================== > --- linux-pm.orig/include/linux/device.h > +++ linux-pm/include/linux/device.h > @@ -1070,6 +1070,16 @@ static inline void dev_pm_syscore_device > #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); > Index: linux-pm/include/linux/pm.h > =================================================================== > --- linux-pm.orig/include/linux/pm.h > +++ linux-pm/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. In principle ACPI/PCI middle-layer/PM domain could have started out by respecting the return values from driver's ->prepare() callbacks in case those existed, but they didn't, and that is the reason to why the SMART_PREPARE is needed. Right? My point is, I don't think we should encourage other middle-layer to support the SMART_PREPARE flag, simply because they should be able to cope without it. To make this more obvious we could try to find a different name of the flag indicating that, or at least make it clear that we don't want it to be used by others than ACPI/PCI via documenting that. > + */ > +#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; > Index: linux-pm/drivers/base/dd.c > =================================================================== > --- linux-pm.orig/drivers/base/dd.c > +++ linux-pm/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(stru > 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); > Index: linux-pm/drivers/base/power/main.c > =================================================================== > --- linux-pm.orig/drivers/base/power/main.c > +++ linux-pm/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; > } > Index: linux-pm/drivers/pci/pci-driver.c > =================================================================== > --- linux-pm.orig/drivers/pci/pci-driver.c > +++ linux-pm/drivers/pci/pci-driver.c > @@ -682,8 +682,11 @@ static int pci_pm_prepare(struct device > > 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)); > } > Index: linux-pm/drivers/acpi/device_pm.c > =================================================================== > --- linux-pm.orig/drivers/acpi/device_pm.c > +++ linux-pm/drivers/acpi/device_pm.c > @@ -965,6 +965,9 @@ int acpi_subsys_prepare(struct device *d > if (ret < 0) > return ret; > > + if (!ret && dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_PREPARE)) > + return 0; So if the driver don't implement the ->prepare() callback, you still want to treat this flag as it has one assigned and that it returns 0? It seems not entirely according to what you have documented about the flag. > + > if (!adev || !pm_runtime_suspended(dev)) > return 0; > > Index: linux-pm/Documentation/driver-api/pm/devices.rst > =================================================================== > --- linux-pm.orig/Documentation/driver-api/pm/devices.rst > +++ linux-pm/Documentation/driver-api/pm/devices.rst > @@ -354,6 +354,20 @@ the phases are: ``prepare``, ``suspend`` > 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 > Index: linux-pm/Documentation/power/pci.txt > =================================================================== > --- linux-pm.orig/Documentation/power/pci.txt > +++ linux-pm/Documentation/power/pci.txt > @@ -961,6 +961,25 @@ dev_pm_ops to indicate that one suspend > .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. I am wondering if we really need to make a statement generic to all "driver PM flags" that these flags must be set at ->probe(). Maybe that is better documented per flag, rather than for all. The reason why I bring it up, is that I would not be surprised if a new flag comes a long and which may be used a bit differently, not requiring that. Of course we can also update that later on, if needed. > + > +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 > Kind regards Uffe