Re: [PATCH] New x86_64 EFI patch

[Bean]

On Sat, Jul 12, 2008 at 10:41 PM, Robert Millan <address@hidden> wrote:
> On Wed, Jul 09, 2008 at 12:31:53AM +0800, Bean wrote:
>> > -- I tried passing video=intelfb to linux; it worked under grub2-pc but
>> > didn't improve anything under efi.
>>
>> intelfb doesn't work. The only way to see console in efi is to use
>> video=vesafb or video=efifb.
>
> How come?  I thought intelfb used the bare hardware.

The video register in efi mode is not setup in the same way as bios.
There are two sets of register. In EFI, set A is completely zero,
while set B have non-zero value. But in bios mode, both set have
non-zero value. I guess this is because bios have text and graphic
mode, while efi only have graphic mode. (text mode in efi is emulated)

>
>> grub2 will detect these options and setup
>> frame buffer for you.
>
> Can you be more specific?  I thought grub was completely agnostic about Linux
> parameters.

In the parameter passed to linux kernel, there are fields for video
adapter information, for example, frame buffer address, line length,
etc. Normally, we don't have to worry about it, but in the case of
efi, we must fill it in, as kernel can't detect the information
properly.

-- 
Bean