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

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Date:	Fri, 28 Feb 2014 14:20:41 +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 14:12, Matthew Garrett wrote:
> On Fri, Feb 28, 2014 at 02:07:58PM +0800, Li, Aubrey wrote:
>> On 2014/2/28 13:56, Matthew Garrett wrote:
>>> Probably, once we've got those patches landed (I've lost track of 
>>> whether they're in 3.13 or aimed at 3.14)
>>
>> You didn't look the reference I quoted in the patch.
>>
>> It's stable if 32/64 bit linux call the corresponding 32/64bit EFI
>> runtime service. Matt Fleming's mixed mode is aiming at 3.15:
>>
>> http://git.kernel.org/cgit/linux/kernel/git/mfleming/efi.git/log/?h=mixed-mode
> 
> It's stable as long as you have the 1:1 mapping patches, which are 
> different to the mixed mode patches. Otherwise it'll work on some 
> hardware and crash on others.
> 
>>> Mm. Not all x86 platforms support cf8/cf9 (Moorestown, for instance) and 
>>> so it's theoretically possible that they'd put some different hardware 
>>> there instead. But then, Moorestown probably has its own reboot code, so 
>>> that may not matter?
>>
>> Yes, Moorestown has its own machine_ops. Instead of the system hanging
>> after issue "reboot" command, I think and suggest CF9 is worth to have a
>> try.
> 
> Writing to arbitrary register addresses isn't a good plan if we're on a 
> platform that might have different hardware there.
> 

Do we have one actually? if we have, I'll remove CF9, if no, I persist
in keeping it, because without it my box can't reboot now, :)

>>>> Reset register address: 0xCF9
>>>> Value to cause reset:   0x6
>>>
>>> Huh. But that's almost exactly what the PCI reboot code would do. Why 
>>> does the PCI method work but the ACPI one fail? Does it really depend on 
>>> ORing the original value with the reset value? Or is the timing just 
>>> somehow marginal?
>>
>> reboot returns at:
>>
>> if (!(acpi_gbl_FADT.flags & ACPI_FADT_RESET_REGISTER))
>>                 return;
>>
>> This is a ACPI bug or intention, who knows.
> 
> Well, how about we figure that out? Is there a full acpi dump of one of 
> these machines somewhere?
> 

Well, I already figured that out. Reset Register Supported flag is ZERO
in FACP table. I attached this table for your interesting.

When I said "this is a ACPI bug or intention", I actually meant it's a
bug or intention created by OEM.

Thanks,
-Aubrey


View attachment "facp.dsl" of type "text/plain" (9129 bytes)