Re: [PATCH 2/5] efi: only set a console mode if the current one is invalid

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

Jan