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

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Date:	Fri, 28 Feb 2014 13:22:37 +0800
From:	"Li, Aubrey" <aubrey.li@...ux.intel.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>
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 2014/2/28 12:56, Matthew Garrett wrote:
> 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.

So it's acceptable to put EFI in the default list.


> 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.

Any hurt known if put it in the default list?

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

Reset register address: 0xCF9
Value to cause reset:   0x6

> 
>> - * 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.
> 

Do we have any spec mentioned that?

Thanks,
-Aubrey
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