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

Michael Brown mcb30 at ipxe.org
Wed Jul 5 10:07:31 UTC 2017

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.


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