RE: [PATCH 5/5] x86_64 EFI support -v3: EFI document

["Huang, Ying" <ying.huang@intel.com>]

>-----Original Message-----
>From: Andi Kleen [mailto:ak@suse.de]
>Subject: Re: [PATCH 5/5] x86_64 EFI support -v3: EFI document
>> The needed code changing is minimal. In fact, I can boot 32bit Linux
>> kernel on my x86_64 EFI machine. With setup as follow:
>>
>> 1. Apply the efi-fb.patch
>Just for the frame buffer, right?

Yes.

>> 2. make efi fb driver not depend on EFI
>> 3. configure kernel as follow:
>>    a. CONFIG_EFI is turned off
>>    b. CONFIG_FB_EFI is turned on
>
>Hmm, how does the 32bit kernel know where the e820 map is passed then?
>With CONFIG_EFI turned off it will just ask the real mode BIOS I think
>and I doubt elilo simulates that.

I have not tested elilo. I use another x86_64 EFI boot loader (it will
be released soon), but elilo works in the same way, and I will test
elilo later. The 16bit entry of kernel (arch/(i386|x86_64)/boot/setup.S)
is not used by elilo. Instead, elilo collects the needed information
defined in include/asm-x86_64/bootsetup.h itself, and passes it to
kernel 32bit entry (arch/(i386|x86_64)/boot/compressed/head.S). For E820
map, the elilo converts the EFI memory map to E820 map in "boot
parameters memory" which is copied to "boot_params" or "x86_boot_params"
by Linux kernel later.

>Or did you apply more patches?

No, just the frame buffer patch.

Best Regards,
Huang Ying
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