Re: [PATCH v2 1/9] vgacon: rework Kconfig dependencies

Hi Arnd,

On Fri, Jul 21, 2023 at 10:29 AM Arnd Bergmann [off-list ref] wrote:

On Fri, Jul 21, 2023, at 06:59, Michael Ellerman wrote:

quoted

Arnd Bergmann [off-list ref] writes:

quoted

From: Arnd Bergmann <arnd@arndb.de>

The list of dependencies here is phrased as an opt-out, but this is missing
a lot of architectures that don't actually support VGA consoles, and some
of the entries are stale:

 - powerpc used to support VGA consoles in the old arch/ppc codebase, but
   the merged arch/powerpc never did

Not disputing this, but how did you come to that conclusion? I grepped
around and couldn't convince myself whether it can work on powerpc or
not. ie. currently it's possible to enable CONFIG_VGA_CONSOLE and
powerpc does have a struct screen_info defined which seems like it would
allow vgacon_startup() to complete.

The VGA console needs both screen_info and vga_con to work. In arch/ppc
we had both, but in arch/powerpc we only retained the screen_info:

$ git grep vga_con v2.6.26 -- arch/ppc arch/ppc64 arch/powerpc
v2.6.26:arch/ppc/platforms/pplus.c:     conswitchp = &vga_con;
v2.6.26:arch/ppc/platforms/prep_setup.c:        conswitchp = &vga_con;

so after arch/ppc was removed, this became impossible to use on both
pplus and prep. These two platforms were also (as far as I can tell)
the only ones to support vga16fb as an alternative to vgacon, but
both platforms were removed later on.

I did use vgacon and vga16fb on CHRP on a second video card
(initialized using Gabriel Paubert's x86 BIOS emulator), but that was
definitely before the advent of arch/powerpc/.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds