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

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Message-ID: <20171019073315.GB20787@kroah.com>
Date:   Thu, 19 Oct 2017 09:33:15 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
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 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>