Update on USB PM state (2.6.15 queue)

[David Brownell <david-b@pacbell.net>]

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I just thought I'd provide a quick update on the state of USB PM,
at least according to my testing(*)  after the patches that are now
in Greg's 2.6.15 queue(**) ... I just forwarded the patch overviews
to this list, the details are on linux-usb-devel.

  - Suspend/resume of the PCI devices through sysfs behaves again ...
    it seems to have broken badly sometime after 2.6.10 or 2.6.11

  - Likewise it behaves through swsusp "shutdown/reboot", both with
    and without devices attached.

  - I have one system on which S1 suspend/resume works, at
    least if I use PS/2 keyboard to trigger wakeup.

  - On some other systems, both S1 and S3 suspend fail; the
    system dies in ACPI during wakeup processing.

As for remote wakeup, using a USB keyboard, that still looks OK
(no regressions needed fixing) except when ACPI kicks in:

  - For "runtime PM" scenarios where individual devices and
    hubs (including root hubs) are suspended, the relevant
    parts of the device tree wake up just fine.

  - For "system PM" scenarios, and with /proc/acpi/wakeup
    tweaked to enable all wakeup events, mixed results:

        * The system where S1 works seems to run into some
          ACPI bugs; the last messages relate to overflow,
          evidently the wakeup signal is never acknowledged.

        * Those other systems don't have any better luck
          when the S1/S3 resume signal is a USB wakeup than
          any other kind of wakeup.

Compared to the last time I tested this, it's good to at least
see the USB remote wakeup signals waking the system up; those
seem to be ACPI improvements.  But it still looks like the
cases I most want to see working (S1, S3) are failing on PCs.

There are a few small USB PM updates on the way from me (call
it all cleanups), and Alan's planning some updates too.

- Dave

(*)  EHCI and OHCI only; no UHCI boxes.

(**) http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/patches/

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