Re: [PATCH 03/14] x86, config: change defaults PHYSICAL_START andPHYSICAL_ALIGN

From: H. Peter Anvin
Date: Fri May 08 2009 - 13:05:12 EST


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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