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Date:   Mon, 16 Oct 2017 16:16:15 -0400 (EDT)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     "Rafael J. Wysocki" <rjw@rjwysocki.net>
cc:     Linux PM <linux-pm@vger.kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux ACPI <linux-acpi@vger.kernel.org>,
        Linux PCI <linux-pci@vger.kernel.org>,
        Linux Documentation <linux-doc@vger.kernel.org>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Kevin Hilman <khilman@kernel.org>,
        Wolfram Sang <wsa@the-dreams.de>, <linux-i2c@vger.kernel.org>,
        Lee Jones <lee.jones@linaro.org>
Subject: Re: [PATCH 01/12] PM / core: Add NEVER_SKIP and SMART_PREPARE driver
 flags
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Message-ID: <Pine.LNX.4.44L0.1710161612080.1377-100000@iolanthe.rowland.org>
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On Mon, 16 Oct 2017, Rafael J. Wysocki wrote:

> From: Rafael J. Wysocki <rafael.j.wysocki@intel.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.

I'm curious: Why does the PCI bus type (and others) do this?  Why 
doesn't it do what the driver says to do?

Alan Stern


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