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    Subject[PATCH] ACPI Suspend: Enable ACPI during resume if SCI_EN is not set
    Date
    From: Rafael J. Wysocki <rjw@sisk.pl>

    ACPI Suspend: Enable ACPI during resume if SCI_EN is not set

    On some machines, like for example MSI Wind U100, the BIOS doesn't
    enable ACPI before returning control to the OS, which sometimes
    causes resume to fail. This is against the ACPI specification,
    which clearly states that "When the platform is waking from an S1, S2
    or S3 state, OSPM assumes the hardware is already in the ACPI mode
    and will not issue an ACPI_ENABLE", but it won't hurt to check the
    SCI_EN bit and enable ACPI during resume from S3 if this bit is not
    set.

    Fortunately, we already have acpi_enable() for that, so use it in the
    resume code path, before executing _BFS, in analogy with the
    resume-from-hibernation code path.

    NOTE: We aren't supposed to set SCI_EN directly, because it's owned
    by the hardware.

    Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
    ---
    drivers/acpi/sleep/main.c | 2 ++
    1 file changed, 2 insertions(+)

    Index: linux-2.6/drivers/acpi/sleep/main.c
    ===================================================================
    --- linux-2.6.orig/drivers/acpi/sleep/main.c
    +++ linux-2.6/drivers/acpi/sleep/main.c
    @@ -200,6 +200,8 @@ static int acpi_suspend_enter(suspend_st
    break;
    }

    + /* If ACPI is not enabled by the BIOS, we need to enable it here. */
    + acpi_enable();
    /* Reprogram control registers and execute _BFS */
    acpi_leave_sleep_state_prep(acpi_state);


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