Re: [PATCH] ACPI suspend: Blacklist boxes that require us to set SCI_EN directly on resume

[Robert Hancock <hancockr@shaw.ca>]

Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@sisk.pl>
> Subject: ACPI suspend: Blacklist boxes that require us to set SCI_EN directly on resume
> 
> Some Apple boxes evidently require us to set SCI_EN on resume
> directly, because if we don't do that, they hung somewhere in the
> resume code path.  Moreover, on these boxes it is not sufficient to
> use acpi_enable() to turn ACPI on during resume.  All of this is
> against the ACPI specification which states that (1) the BIOS is
> supposed to return from the S3 sleep state with ACPI enabled
> (SCI_EN set) and (2) the SCI_EN bit is owned by the hardware and we
> are not supposed to change it.
> 
> For this reason, blacklist the affected systems so that the SCI_EN
> bit is set during resume on them.
> 
> [NOTE: Unconditional setting SCI_EN for all system on resume doesn't
>  work, because it makes some other systems crash (that's to be
>  expected).  Also, it is not entirely clear right now if all of the
>  Apple boxes require this workaround.]

This is rather gross. The usual question arises, why does Windows work 
without such a hack? Maybe there is no better solution for now, but 
somebody should really look into why the behavior is different in Linux..