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

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Date:   Mon, 16 Oct 2017 16:16:15 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
cc:     Linux PM <linux-pm@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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: [PATCH 01/12] PM / core: Add NEVER_SKIP and SMART_PREPARE driver
 flags

On Mon, 16 Oct 2017, 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.

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