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    Subject[PATCH 9-10/10] Allow subsystems to avoid using sysdevs for defining "core" PM callbacks
    On Saturday, March 12, 2011, Rafael J. Wysocki wrote:
    > Hi,
    > On Thursday, March 10, 2011, Rafael J. Wysocki wrote:
    > > There are multiple problems with sysdevs, or struct sys_device objects to
    > > be precise, that are so annoying that some people have started to think
    > > of removind them entirely from the kernel. To me, personally, the most
    > > obvious issue is the way sysdevs are used for defining suspend/resume
    > > callbacks to be executed with one CPU on-line and interrupts disabled.
    > > Greg and Kay may tell you more about the other problems with sysdevs. :-)
    > >
    > > Some subsystems need to carry out certain operations during suspend after
    > > we've disabled non-boot CPUs and interrupts have been switched off on the
    > > only on-line one. Currently, the only way to achieve that is to define
    > > sysdev suspend/resume callbacks, but this is cumbersome and inefficient.
    > > Namely, to do that, one has to define a sysdev class providing the callbacks
    > > and a sysdev actually using them, which is excessively complicated. Moreover,
    > > the sysdev suspend/resume callbacks take arguments that are not really used
    > > by the majority of subsystems defining sysdev suspend/resume callbacks
    > > (or even if they are used, they don't really _need_ to be used, so they
    > > are simply unnecessary). Of course, if a sysdev is only defined to provide
    > > suspend/resume (and maybe shutdown) callbacks, there's no real reason why
    > > it should show up in sysfs.
    > >
    > > For this reason, I thought it would be a good idea to provide a simpler
    > > interface for subsystems to define "very late" suspend callbacks and
    > > "very early" resume callbacks (and "very late" shutdown callbacks as well)
    > > without the entire bloat related to sysdevs. The interface is introduced
    > > by the first of the following patches, while the second patch converts some
    > > sysdev users related to the x86 architecture to using the new interface.
    > >
    > > I believe that call sysdev users who need to define suspend/resume/shutdown
    > > callbacks may be converted to using the interface provided by the first patch,
    > > which in turn should allow us to convert the remaining sysdev functionality
    > > into "normal" struct device interfaces. Still, even if that turns out to be
    > > too complicated, the bloat reduction resulting from the second patch kind of
    > > shows that moving at least some sysdev users to a simpler interface (like in
    > > the first patch) is a good idea anyway.
    > >
    > > This is a proof of concept, so the patches have not been tested. Please be
    > > extrememly careful, because they touch sensitive code, so to speak. In the
    > > majority of cases the changes are rather straightforward, but there are some
    > > more interesting cases as well (io_apic.c most importantly).
    > Since Greg likes the idea and there haven't been any objections so far, here's
    > the official submission. The patches have been tested on HP nx6325 and
    > Toshiba Portege R500.
    > Patch [1/8] is regareded as 2.6.38 material, following Greg's advice. The
    > other patches in the set are regarded as 2.6.39 material. The last one
    > obviously depends on all of the previous ones.
    > [1/8] - Introduce struct syscore_ops for registering operations to be run on
    > one CPU during suspend/resume/shutdown.
    > [2/8] - Convert sysdev users in arch/x86 to using struct syscore_ops.
    > [3/8] - Make ACPI use struct syscore_ops for irqrouter_resume().
    > [4/8] - Make timekeeping use struct syscore_ops for suspend/resume.
    > [5/8] - Make Intel IOMMU use struct syscore_ops for suspend/resume.
    > [6/8] - Make KVM use struct syscore_ops for suspend/resume.
    > [7/8] - Make cpufreq use struct syscore_ops for boot CPU suspend/resume.
    > [8/8] - Introduce config switch allowing architectures to skip sysdev
    > suspend/resume/shutdown code.
    > If there are no objectsions, I'd like to push these patches through the suspend
    > tree.

    A little followup with two ARM-related patches.

    [9/10] - Make sh drivers use struct syscore_ops for suspend/resume (instead of
    [10/10] - Use struct syscore_ops for suspend/resume (instead of sysdevs) in
    core ARM code.


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