linux-kernel - Re: [PATCH] ACPI suspend: Blacklist boxes that require us to set SCI

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Message-ID:  <49225697.90804@shaw.ca>
Date:	Mon, 17 Nov 2008 23:45:59 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	linux-kernel@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org
Subject:  Re: [PATCH] ACPI suspend: Blacklist boxes that require us to set
 SCI_EN directly on resume

Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@...k.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..

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