On Fri, Mar 31, 2023 at 08:51:46AM +0200, Jan Beulich wrote: > On 30.03.2023 18:17, Roger Pau Monné wrote: > > On Thu, Mar 30, 2023 at 06:07:57PM +0200, Jan Beulich wrote: > >> On 30.03.2023 17:44, Roger Pau Monné wrote: > >>> I guess I'm slightly confused by the usage of both GOP and StdOut, I > >>> would assume if we have a gop, and can correctly initialize it there's > >>> no need to fiddle with StdOut also? > >> > >> Setting the GOP mode is done last before exiting boot services; this > >> may be a graphics mode which doesn't support a text output protocol. > > > > Right, that's what I was missing. I assumed that all modes available > > in GOP would be compatible with the ConOut mode. > > > > Would you be OK with leaving StdOut as-is when booted from multiboot2, > > or there's a chance of things not being properly setup? > > On modern UEFI it may be unlikely, but I think it's not impossible (see > below). > > > IMO it's not very friendly to change the StdOut mode if not explicitly > > requested, as in the multiboot2 case that gets setup by the > > bootloader. > > May get set up, that is. If it was set up, then yes, we probably should > leave it alone unless told to use another mode. I.e. no vga= or > vga=current should minimally result in no further mode change. Aiui we > can't easily honor vga=gfx-... in that case, so leaving the mode alone > there may also be better than trying to guess a mode. The only time > where I would think it would be nice to switch by default even in the > xen.gz case is if the boot loader handed us the screen in some text > mode.
How would you detect such case? ConOut is always text-mode like because it's a EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL interface. Would it be a matter of checking whether the current GOP mode is valid, and if so leave it as-is unless told otherwise by a command line parameter? I would also like to avoid the unconditional resizing of the ConOut interface that's done in efi_console_set_mode(), as that has the size effect of changing the GOP mode, so I would only call efi_console_set_mode() is there's no gop. Not sure it's meaningful to change the ConOut number of cols/rows if there's no GOP, maybe it's possible to have some kind of screen that's usable for EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL but not as a GOP? Thanks, Roger.
