linux-kernel - Re: [RFC PATCH] drivers core: cpu: add hotplug callback to update cpu

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Message-ID: <20190131160559.GA32759@e107155-lin>
Date:   Thu, 31 Jan 2019 16:05:59 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jisheng Zhang <jszhang@...vell.com>,
        Steve Longerbeam <steve_longerbeam@...tor.com>,
        Eugeniu Rosca <roscaeugeniu@...il.com>,
        Joshua Frkuska <joshua_frkuska@...tor.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [RFC PATCH] drivers core: cpu: add hotplug callback to update
 cpu_dev state to resumed

On Thu, Jan 31, 2019 at 12:48:49AM +0100, Rafael J. Wysocki wrote:
> On Friday, January 25, 2019 4:09:06 PM CET Sudeep Holla wrote:
> > 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
> > onlin. Generally when the secondary CPUs are hotplugged back is 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 are
> > 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.
> >
> > Just fix the warning by updating the device state quite early.
> >
> > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> > Reported-by: Jisheng Zhang <jszhang@...vell.com>
> > Reported-by: Steve Longerbeam <slongerbeam@...il.com>
> > Reported-by: Eugeniu Rosca <erosca@...adit-jv.com>
> > Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> > ---
> >  drivers/base/cpu.c         | 20 +++++++++++++++++++-
> >  include/linux/cpuhotplug.h |  1 +
> >  2 files changed, 20 insertions(+), 1 deletion(-)
> >
> > Hi Rafael,
> >
> > This is getting reported for quite some time. Let me know if you have
> > better solution to fix this harmless yet annoying warnings during system
> > resume.
>
> I'd rather have a flag in struct dev_pm_info that will cause the message to
> be suppressed if set.
>
> It could be used for other purposes too then in princple (like skipping the
> creation of empty "power" attr groups in sysfs for devices that don't
> need them etc.).
>
Thanks for the suggestion. I did quick hack and came up with something
below. I wanted to run through you once before I materialise it into
a formal patch to check if I understood your suggestion correctly.
We can move no_pm_required outside dev_pm_info struct and rename with
any better names.

-->8

diff --git i/drivers/base/cpu.c w/drivers/base/cpu.c
index eb9443d5bae1..b61f9772ed33 100644
--- i/drivers/base/cpu.c
+++ w/drivers/base/cpu.c
@@ -379,6 +379,7 @@ int register_cpu(struct cpu *cpu, int num)
 	cpu->dev.bus->uevent = cpu_uevent;
 #endif
 	cpu->dev.groups = common_cpu_attr_groups;
+	cpu->dev.power.no_pm_required = true;
 	if (cpu->hotpluggable)
 		cpu->dev.groups = hotplugable_cpu_attr_groups;
 	error = device_register(&cpu->dev);
@@ -427,6 +428,7 @@ __cpu_device_create(struct device *parent, void *drvdata,
 	dev->parent = parent;
 	dev->groups = groups;
 	dev->release = device_create_release;
+	dev->power.no_pm_required = true;
 	dev_set_drvdata(dev, drvdata);
 
 	retval = kobject_set_name_vargs(&dev->kobj, fmt, args);
diff --git i/drivers/base/power/main.c w/drivers/base/power/main.c
index 0992e67e862b..ed1b133f73db 100644
--- i/drivers/base/power/main.c
+++ w/drivers/base/power/main.c
@@ -124,6 +124,8 @@ void device_pm_unlock(void)
  */
 void device_pm_add(struct device *dev)
 {
+	if (dev->power.no_pm_required)
+		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 +144,8 @@ void device_pm_add(struct device *dev)
  */
 void device_pm_remove(struct device *dev)
 {
+	if (dev->power.no_pm_required)
+		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 i/drivers/base/power/sysfs.c w/drivers/base/power/sysfs.c
index d713738ce796..54c1bfec396e 100644
--- i/drivers/base/power/sysfs.c
+++ w/drivers/base/power/sysfs.c
@@ -648,6 +648,9 @@ int dpm_sysfs_add(struct device *dev)
 {
 	int rc;
 
+	if (dev->power.no_pm_required)
+		return 0;
+
 	rc = sysfs_create_group(&dev->kobj, &pm_attr_group);
 	if (rc)
 		return rc;
diff --git i/include/linux/pm.h w/include/linux/pm.h
index 0bd9de116826..300ab9f0b858 100644
--- i/include/linux/pm.h
+++ w/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_required:1;
 	bool			early_init:1;	/* Owned by the PM core */
 	bool			direct_complete:1;	/* Owned by the PM core */
 	u32			driver_flags;