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

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Message-ID: <CAMuHMdVszR+oZi8x8L0iXx=ydTiaNUZxToBSdf=2ZH5t85+D_Q@mail.gmail.com>
Date:   Mon, 24 Jul 2023 14:07:25 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Arnd Bergmann <arnd@...nel.org>, linux-fbdev@...r.kernel.org,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Helge Deller <deller@....de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        "David S . Miller" <davem@...emloft.net>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Borislav Petkov <bp@...en8.de>, Brian Cain <bcain@...cinc.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dave Airlie <airlied@...il.com>,
        Deepak Rawat <drawat.floss@...il.com>,
        Dexuan Cui <decui@...rosoft.com>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
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Subject: Re: [PATCH v2 1/9] vgacon: rework Kconfig dependencies

Hi Arnd,

On Fri, Jul 21, 2023 at 10:29 AM Arnd Bergmann <arnd@...db.de> wrote:
> On Fri, Jul 21, 2023, at 06:59, Michael Ellerman wrote:
> > Arnd Bergmann <arnd@...nel.org> writes:
> >> From: Arnd Bergmann <arnd@...db.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@...ux-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