linux-kernel - Re: [tip:x86/reboot] [PATCH] x86: Try the BIOS reboot method before the PCI reboot method

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Date:	Sun, 6 Apr 2014 18:40:23 +0100
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	"Li, Aubrey" <aubrey.li@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>, hpa@...or.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	rostedt@...dmis.org, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org,
	Adam Williamson <awilliam@...hat.com>
Subject: Re: [tip:x86/reboot] [PATCH] x86: Try the BIOS reboot method before
 the PCI reboot method

On Fri, 4 Apr 2014 16:13:59 +0100
Matthew Garrett <mjg59@...f.ucam.org> wrote:

> On Fri, Apr 04, 2014 at 09:38:57PM +0800, Li, Aubrey wrote:
> 
> > I don't think there is enough justification to revert the patch. We
> > introduce EFI into the default list, we didn't see any reason to remove
> > it out so far.
> 
> We should be using the EFI method, yes. But it seems that CF9 isn't 
> safe, so we should drop that.
>

Windows does not use CF9 and there are known, documented cases where CF9
will not work reliably. That includes reliable reboot on some Baytrail
systems. (Erratum VLT60 and VLT62).

So we really shouldn't be doing 0xCF9 except as a last resort if we are
still alive and have been through the official reboot methods.

Alan

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