linux-kernel - Re: [patch] x86: Introduce BOOT_EFI and BOOT

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Message-ID: <20140228045637.GA28257@srcf.ucam.org>
Date:	Fri, 28 Feb 2014 04:56:37 +0000
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	"Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc:	"alan@...ux.intel.com" <alan@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...ux.intel.com>, Len.Brown@...el.com,
	Adam Williamson <awilliam@...hat.com>
Subject: Re: [patch] x86: Introduce BOOT_EFI and BOOT_CF9 into the reboot
 sequence loop

On Fri, Feb 28, 2014 at 12:11:57PM +0800, Li, Aubrey wrote:
> This patch is to introduce BOOT_EFI and BOOT_CF9 in the reboot sequence
> loop, to fix the reboot problem on the known Intel Bay Trail-T based
> platform, for example, ASUS-T100 and Dell Venue 8/11 Pro. These
> platforms don't support ACPI reboot, we expect to call EFI runtime
> service to handle this case, and CF9 is an alternate after EFI.

EFI reboot is still somewhat unreliable - it may be safe after the 
recent patches to provide a 1:1 mapping. CF9 is, as far as I know, not 
part of any spec, so it seems like a bad idea to put it in the default 
list.

What do the ACPI reboot vectors look like on these systems?

> - * 3) If still alive, write to the ACPI reboot register again
> - * 4) If still alive, write to the keyboard controller again
> + * 3) If still alive, call EFI runtime service
> + * 4) If still alive, write to the PCI IO port 0xCF9

This is definitely incorrect. The ACPI write *must* occur twice in order 
to be effective on various systems. EFI shouldn't be attempted until 
after the second ACPI write.

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