linux-kernel - Re: [PATCH 03/14] x86, config: change defaults PHYSICAL_START and PHYSICAL

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Date:	Fri, 08 May 2009 10:01:04 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Sam Ravnborg <sam@...nborg.org>
CC:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	linux-kernel@...r.kernel.org, vgoyal@...hat.com, hbabu@...ibm.com,
	kexec@...ts.infradead.org, ying.huang@...el.com, mingo@...e.hu,
	tglx@...utronix.de, ebiederm@...ssion.com
Subject: Re: [PATCH 03/14] x86, config: change defaults PHYSICAL_START and
 PHYSICAL_ALIGN

Sam Ravnborg wrote:
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 039c3f0..13b3a5a 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -1455,17 +1455,20 @@ config KEXEC_JUMP
>>  
>>  config PHYSICAL_START
>>  	hex "Physical address where the kernel is loaded" if (EMBEDDED || CRASH_DUMP)
>> -	default "0x1000000" if X86_NUMAQ
>> -	default "0x200000" if X86_64
>> -	default "0x100000"
>> +	default "0x400000" if EMBEDDED
>> +	default "0x1000000"
>>  	---help---
>>  	  This gives the physical address where the kernel is loaded.
>>  
>>  	  If kernel is a not relocatable (CONFIG_RELOCATABLE=n) then
>>  	  bzImage will decompress itself to above physical address and
>> -	  run from there. Otherwise, bzImage will run from the address where
>> -	  it has been loaded by the boot loader and will ignore above physical
>> -	  address.
>> +	  run from there. Otherwise, bzImage will run from the either
>> +	  the above physical address or where it has been loaded by
>> +	  the boot loader, whichever is higher.
>> +
>> +	  For embedded machines with very small memory (less than
>> +	  about 24 MB) this may need to be adjusted downward from the
>> +	  default value of 0x1000000 (16 MB).
> 
> But in the above you say that default is "0x400000" if EMBEDDED
> That is in contradiction with the help - no?
> 

0x1000000 really should be the default value.  The "0x400000" if
EMBEDDED I put in to make the risk of throwing something surprising on
embedded people somewhat smaller; I'm not sure if it should go away
entirely.  Even if it doesn't, I do think referring to 16 MB as the
"default value" is right.

BTW, it would be nice to have Kconfig deal with:

a) numbers that must be powers of 2;
b) suffixes like "16M" instead of "0x1000000".  ;)

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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