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    SubjectRe: [RFC][PATCH 0/2] Allow subsystems to avoid using sysdevs for defining "core" PM callbacks
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    On Thursday, March 10, 2011, Kay Sievers wrote:
    > On Thu, 2011-03-10 at 01:31 +0100, 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.
    >
    > Do I read that right? We get rid of the entire dance of creating
    > sysdevs/sysdev_classes and the pointless and broken stuff in /sys?

    That's the plan at least.

    > We just dynamically maintain a list of devices/operations, which is
    > list-executed when needed?
    >
    > These new "core" operations are not included in every device but only
    > global per subsystem, just like the sysdev_class did earlier?

    Yup.

    > Looks all like a nice plan to me.

    Good. :-)

    Thanks,
    Rafael


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