linux-kernel - Re: [Update][PATCH v2 01/12] PM / core: Add NEVER_SKIP and SMART

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Date:   Fri, 20 Oct 2017 13:11:22 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        Lukas Wunner <lukas@...ner.de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Alan Stern <stern@...land.harvard.edu>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux Documentation <linux-doc@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kevin Hilman <khilman@...nel.org>,
        Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
        Lee Jones <lee.jones@...aro.org>
Subject: Re: [Update][PATCH v2 01/12] PM / core: Add NEVER_SKIP and SMART_PREPARE driver flags

On Thursday, October 19, 2017 9:33:15 AM CEST Greg Kroah-Hartman wrote:
> On Thu, Oct 19, 2017 at 01:17:31AM +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > 
> > 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 <rafael.j.wysocki@...el.com>
> 
> Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Thanks!

Does it also apply to the other patches in the series?

I'd like to queue up the core patches for 4.15 as they are specifically
designed to only affect the drivers that actually set the flags, so there
shouldn't be any regression resulting from them, and I'd like to be
able to start using the flags in drivers going forward.

Thanks,
Rafael