RE: legacy-bios and uefi boot usb stick

[John Frankish]

>>>>>> I've made a couple of dual legacy-bios/uefi boot usb sticks using 
>>>>>> grub-2.00.
>>>>>>
>>>>>> Both of the usb sticks will uefi boot linux, but there appears to be a 
>>>>>> problem with legacy-bios boot of linux.
>>>>>>
>>>>>> One of the usb sticks gives an "invalid partition table!" error
>>>>>>
>>>>> What displays the message ? GRUB or the BIOS firmware ? Do you get the 
>>>>> GRUB rescue prompt ?
>>>>> Some BIOS firmwares require that a primary partition has the boot flag.
>>>>>
>>>> It seems as though it is grub displaying the message.
>>>>
>>>> In one case I get the "invalid partition table!" message and have to 
>>>> cycle the power
>>>>
>>> If the message was displayed by GRUB, I believe that you would at least get 
>>> the GRUB rescue prompt.
>>>
>> After videoing the screen, I see that the error message is:
>> 
>> Error: file '/EFI/BOOT/grub/i386-pc/efi_gop.mod' not found
>> Error: no suitable video modes found
>> 
>> efi_gop* is in i386-efi and x86_64-efi, but not in i386-pc.
>> 
> Which is correct, this video driver is available on EFI platform only.
>
>> If I add "vga=792" then grub gives an error message that this is depreciated,
>> but the frame buffer is set to 1024x768. If I try "vga=895" the native 
>> resolution of 1366x768
>> is not set even though it is present in "Xvesa -listmodes" and is set with 
>> uefi boot.
>> 
> It is not clear what "is not set" means here (is not set in grub or in 
> Linux), but your grub.cfg
> in original post does not load any video driver for for legacy BIOS.
> 
> In current grub you can simply use "insmod all_video" which will attempt to 
> load all
> available video drivers. Usually only one of them actually works. This should 
> handle both legacy BIOS and EFI.
> 
"insmod all_video" did the trick and I finally get 1366x768 with a legacy-bios 
boot - thanks for this :)

$ dmesg | grep fb 
...
vesafb: mode is 1366x768x32, linelength=5504, pages=0
vesafb: scrolling: redraw
vesafb: Truecolor: size=8:8:8:8, shift=24:16:8:0
vesafb: framebuffer at 0xe0000000, mapped to 0xffffc90000800000, using 4160k, 
total 4160k
fb0: VESA VGA frame buffer device

With a legacy-bios boot several seconds pass before the grub menu comes up, 
which I guess is grub trying the video drivers one by one. Is there a way to 
tell which video driver was used - other than trying them one by one?