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Date:   Wed, 20 Feb 2019 10:28:54 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jisheng Zhang <jszhang@...vell.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Steve Longerbeam <slongerbeam@...il.com>,
        Eugeniu Rosca <erosca@...adit-jv.com>,
        Joshua Frkuska <joshua_frkuska@...tor.com>,
        Eugeniu Rosca <roscaeugeniu@...il.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v3] drivers: base: add support to skip power management in device/driver model

On Thursday, February 14, 2019 7:29:10 PM CET Sudeep Holla wrote:
> All device objects in the driver model contain fields that control the
> handling of various power management activities. However, it's not
> always useful. There are few instances where pseudo devices are added
> to the model just to take advantage of many other features like
> kobjects, udev events, and so on. One such example is cpu devices and
> their caches.
> 
> The sysfs for the cpu caches are managed by adding devices with cpu
> as the parent in cpu_device_create() when secondary cpu is brought
> online. Generally when the secondary CPUs are hotplugged back in as part
> of resume from suspend-to-ram, we call cpu_device_create() from the cpu
> hotplug state machine while the cpu device associated with that CPU is
> not yet ready to be resumed as the device_resume() call happens bit
> later. It's not really needed to set the flag is_prepared for cpu
> devices as they are mostly pseudo device and hotplug framework deals
> with state machine and not managed through the cpu device.
> 
> This often results in annoying warning when resuming:
> Enabling non-boot CPUs ...
> CPU1: Booted secondary processor
>  cache: parent cpu1 should not be sleeping
> CPU1 is up
> CPU2: Booted secondary processor
>  cache: parent cpu2 should not be sleeping
> CPU2 is up
> .... and so on.
> 
> So in order to fix these kind of errors, we could just completely avoid
> doing any power management related initialisations and operations if
> they are not used by these devices.
> 
> Lets add no_pm_required flags to indicate that the device doesn't
> require any sort of pm activities and all of them can be completely
> skipped. We can use the same flag to also avoid adding not used *power*
> sysfs entries for these devices. For now, lets use this for cpu cache
> devices.
> 
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Reviewed-by: Ulf Hansson <ulf.hansson@...aro.org>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>  drivers/base/cpu.c         |  1 +
>  drivers/base/power/main.c  |  7 +++++++
>  drivers/base/power/sysfs.c |  6 ++++++
>  include/linux/device.h     | 10 ++++++++++
>  include/linux/pm.h         |  1 +
>  5 files changed, 25 insertions(+)
> 
> v2->v3:
> 	- renamed no_pm_required to no_pm
> 	- fixed the wrong comment in device_pm_add
> 	- add missing check in dpm_sysfs_remove reported by Eugeniu
> 	- added Ulf's reviewed-by tag
> 
> v1->v2:
> 	- dropped setting the flag for cpu devices, for now just cpu caches
> 	  will make use of this new flag.
> 
> RFC->v1:
> 	- dropped the idea of adding cpu hotplug callback to deal just
> 	  with cpu devices, instead add a new flag in the device pm_info
> 	  structure
> 
> [RFC] : https://marc.info/?l=linux-pm&m=154842896407904&w=2
> [v1] : https://marc.info/?l=linux-pm&m=154946578717730&w=2
> [v2] : https://marc.info/?l=linux-pm&m=155005931507485&w=2
> 
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index eb9443d5bae1..6ce93a52bf3f 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -427,6 +427,7 @@ __cpu_device_create(struct device *parent, void *drvdata,
>  	dev->parent = parent;
>  	dev->groups = groups;
>  	dev->release = device_create_release;
> +	device_set_pm_not_required(dev);
>  	dev_set_drvdata(dev, drvdata);
> 
>  	retval = kobject_set_name_vargs(&dev->kobj, fmt, args);
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index 0992e67e862b..6a473004abe6 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -124,6 +124,10 @@ void device_pm_unlock(void)
>   */
>  void device_pm_add(struct device *dev)
>  {
> +	/* Skip pm setup/initialisation */
> +	if (device_pm_not_required(dev))
> +		return;
> +
>  	pr_debug("PM: Adding info for %s:%s\n",
>  		 dev->bus ? dev->bus->name : "No Bus", dev_name(dev));
>  	device_pm_check_callbacks(dev);
> @@ -142,6 +146,9 @@ void device_pm_add(struct device *dev)
>   */
>  void device_pm_remove(struct device *dev)
>  {
> +	if (device_pm_not_required(dev))
> +		return;
> +
>  	pr_debug("PM: Removing info for %s:%s\n",
>  		 dev->bus ? dev->bus->name : "No Bus", dev_name(dev));
>  	complete_all(&dev->power.completion);
> diff --git a/drivers/base/power/sysfs.c b/drivers/base/power/sysfs.c
> index d713738ce796..5e8d4867c4da 100644
> --- a/drivers/base/power/sysfs.c
> +++ b/drivers/base/power/sysfs.c
> @@ -648,6 +648,10 @@ int dpm_sysfs_add(struct device *dev)
>  {
>  	int rc;
> 
> +	/* No need to create pm sysfs if explicitly disabled */
> +	if (device_pm_not_required(dev))
> +		return 0;
> +
>  	rc = sysfs_create_group(&dev->kobj, &pm_attr_group);
>  	if (rc)
>  		return rc;
> @@ -727,6 +731,8 @@ void rpm_sysfs_remove(struct device *dev)
> 
>  void dpm_sysfs_remove(struct device *dev)
>  {
> +	if (device_pm_not_required(dev))
> +		return;
>  	sysfs_unmerge_group(&dev->kobj, &pm_qos_latency_tolerance_attr_group);
>  	dev_pm_qos_constraints_destroy(dev);
>  	rpm_sysfs_remove(dev);
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 6cb4640b6160..53028636fe39 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -1165,6 +1165,16 @@ static inline bool device_async_suspend_enabled(struct device *dev)
>  	return !!dev->power.async_suspend;
>  }
> 
> +static inline bool device_pm_not_required(struct device *dev)
> +{
> +	return dev->power.no_pm;
> +}
> +
> +static inline void device_set_pm_not_required(struct device *dev)
> +{
> +	dev->power.no_pm = true;
> +}
> +
>  static inline void dev_pm_syscore_device(struct device *dev, bool val)
>  {
>  #ifdef CONFIG_PM_SLEEP
> diff --git a/include/linux/pm.h b/include/linux/pm.h
> index 0bd9de116826..8869ce7b5fa6 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -592,6 +592,7 @@ struct dev_pm_info {
>  	bool			is_suspended:1;	/* Ditto */
>  	bool			is_noirq_suspended:1;
>  	bool			is_late_suspended:1;
> +	bool			no_pm:1;
>  	bool			early_init:1;	/* Owned by the PM core */
>  	bool			direct_complete:1;	/* Owned by the PM core */
>  	u32			driver_flags;
> --

Applied, thanks!

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