Re: [PATCH 01/12] PM / core: Add NEVER_SKIP and SMART_PREPARE driver flags

[Alan Stern]

On Mon, 16 Oct 2017, Rafael J. Wysocki wrote:

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