linux-kernel - Re: [PATCH 1/4] ACPI: Support

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Message-ID: <20140617144614.GA16934@srcf.ucam.org>
Date:	Tue, 17 Jun 2014 15:46:15 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	lenb@...nel.org, robert.moore@...el.com, lv.zheng@...el.com,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, bhelgaas@...gle.com
Subject: Re: [PATCH 1/4] ACPI: Support _OSI("Darwin") correctly

On Tue, Jun 17, 2014 at 02:11:36PM +0200, Rafael J. Wysocki wrote:
> On Sunday, June 01, 2014 12:33:53 PM Matthew Garrett wrote:
> > Apple hardware queries _OSI("Darwin") in order to determine whether the
> > system is running OS X, and changes firmware behaviour based on the answer.
> > The most obvious difference in behaviour is that Thunderbolt hardware is
> > forcibly powered down unless the system is running OS X. The obvious solution
> > would be to simply add Darwin to the list of supported _OSI strings, but this
> > causes problems.
> > 
> > Recent Apple hardware includes two separate methods for checking _OSI
> > strings. The first will check whether Darwin is supported, and if so will
> > exit. The second will check whether Darwin is supported, but will then
> > continue to check for further operating systems. If a further operating
> > system is found then later firmware code will assume that the OS is not OS X.
> > This results in the unfortunate situation where the Thunderbolt controller is
> > available at boot time but remains powered down after suspend.
> > 
> > The easiest way to handle this is to special-case it in the Linux-specific
> > OSI handling code. If we see Darwin, we should answer true and then disable
> > all other _OSI vendor strings.
> > 
> > Signed-off-by: Matthew Garrett <matthew.garrett@...ula.com>
> 
> Does applying this patch without the rest of the series makes things worse
> or better on the machines in question (or perhaps it doesn't matter at all
> alone)?

On its own, I think this will do nothing.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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