[ipxe-devel] VGA resolution issue ---IPXE.EFI PXE boot

[Christian Nilsson]

On Wed, Jul 5, 2017 at 12:07 PM, Michael Brown <mcb30 at ipxe.org> wrote:
> On 05/07/17 10:27, dangdehua wrote:
>>
>> Recently came across this problem: the resolution is not valid in OS when
>> I set “vga=0x314” in kernel cmdline with ipxe.efi boot.
>>
>> In EFI BIOS platform, Although I set “vga=0x314” in kernel cmdline, the
>> actual resolution is 0x317(1024*768) when boot in OS.
>>
>> Is there any method/command to set VGA resolution? Which code will be
>> changed to support the feature?
>
>
> In a BIOS boot, the "vga=..." parameter is interpreted by the bootloader
> (i.e. iPXE) and used to modify the vid_mode field within the bzImage header.
>
> In a UEFI boot, iPXE treats the kernel as being a generic UEFI executable,
> and just passes along the "vga=..." parameter together with all other
> parameters as part of the kernel command line.  It would then be the
> responsibility of the kernel's EFI stub to interpret this.  There is no
> dedicated method equivalent to the vid_mode field for iPXE to express the
> concept of "desired video mode".
>
> From a very quick look at the kernel, it seems that the EFI stub doesn't
> currently have any handling for a "vga=" parameter.  There may be some
> UEFI-specific equivalent kernel command line parameter that I am not aware
> of.
>
> Michael

Best way to handle this in EFI land is probably to use the kernels
EFIFB implementation which reads the native EFI resolution, I believe
that this resolution can be changed by iPXE if the console command and
FB is enabled on compile time.

Another option is to use the video= kernel cmdline option instead with
uvesa_fb or similar.

/Christian