linux-kernel - Re: [PATCH v2 3/4] PM: sleep: Use DPM_FLAG_SMART

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Message-ID: <CAJZ5v0iT5j3S=VtRo+uHEaiM+fYah=mRr7c3vZnvguNnOY3TPQ@mail.gmail.com>
Date: Wed, 19 Feb 2025 13:14:36 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>, Linux PM <linux-pm@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, Alan Stern <stern@...land.harvard.edu>, 
	Linux PCI <linux-pci@...r.kernel.org>, Ulf Hansson <ulf.hansson@...aro.org>, 
	Johan Hovold <johan@...nel.org>, Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, 
	Jon Hunter <jonathanh@...dia.com>, Linux ACPI <linux-acpi@...r.kernel.org>, 
	Mika Westerberg <mika.westerberg@...ux.intel.com>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v2 3/4] PM: sleep: Use DPM_FLAG_SMART_SUSPEND conditionally

On Tue, Feb 18, 2025 at 11:20 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Tue, Feb 18, 2025 at 09:16:48PM +0100, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> > A recent discussion has revealed that using DPM_FLAG_SMART_SUSPEND
> > unconditionally is generally problematic because it may lead to
> > situations in which the device's runtime PM information is internally
> > inconsistent or does not reflect its real state [1].
> >
> > For this reason, change the handling of DPM_FLAG_SMART_SUSPEND so that
> > it is only taken into account if it is consistently set by the drivers
> > of all devices having any PM callbacks throughout dependency graphs in
> > accordance with the following rules:
> >
> >  - The "smart suspend" feature is only enabled for devices whose drivers
> >    ask for it (that is, set DPM_FLAG_SMART_SUSPEND) and for devices
> >    without PM callbacks unless they have never had runtime PM enabled.
> >
> >  - The "smart suspend" feature is not enabled for a device if it has not
> >    been enabled for the device's parent unless the parent does not take
> >    children into account or it has never had runtime PM enabled.
> >
> >  - The "smart suspend" feature is not enabled for a device if it has not
> >    been enabled for one of the device's suppliers taking runtime PM into
> >    account unless that supplier has never had runtime PM enabled.
> >
> > Namely, introduce a new device PM flag called smart_suspend that is only
> > set if the above conditions are met and update all DPM_FLAG_SMART_SUSPEND
> > users to check power.smart_suspend instead of directly checking the
> > latter.
> >
> > At the same time, drop the power.set_active flage introduced recently
> > in commit 3775fc538f53 ("PM: sleep: core: Synchronize runtime PM status
> > of parents and children") because it is now sufficient to check
> > power.smart_suspend along with the dev_pm_skip_resume() return value
> > to decide whether or not pm_runtime_set_active() needs to be called
> > for the device.
> >
> > Link: https://lore.kernel.org/linux-pm/CAPDyKFroyU3YDSfw_Y6k3giVfajg3NQGwNWeteJWqpW29BojhQ@mail.gmail.com/  [1]
> > Fixes: 7585946243d6 ("PM: sleep: core: Restrict power.set_active propagation")
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > Reviewed-by: Ulf Hansson <ulf.hansson@...aro.org>
>
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com> # drivers/pci

Thanks!