linux-kernel - Re: [PATCH 2/2] efi: earlycon: Add support for generic framebuffers and move to fbdev subsystem

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Date:   Thu, 28 Jul 2022 17:16:32 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Markuss Broks <markuss.broks@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        Ard Biesheuvel <ardb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Helge Deller <deller@....de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Borislav Petkov <bp@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Michal Suchanek <msuchanek@...e.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Wei Ming Chen <jj251510319013@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Tony Lindgren <tony@...mide.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH 2/2] efi: earlycon: Add support for generic framebuffers
 and move to fbdev subsystem

On Thu, Jul 28, 2022 at 4:57 PM Markuss Broks <markuss.broks@...il.com> wrote:
> On 7/28/22 17:48, Arnd Bergmann wrote:
> > On Thu, Jul 28, 2022 at 4:28 PM Markuss Broks <markuss.broks@...il.com> wrote:
> >>
> >> Add early console support for generic linear framebuffer devices.
> >> This driver supports probing from cmdline early parameters
> >> or from the device-tree using information in simple-framebuffer node.
> >> The EFI functionality should be retained in whole.
> >> The driver was disabled on ARM because of a bug in early_ioremap
> >> implementation on ARM.
> >>
> >> Signed-off-by: Markuss Broks <markuss.broks@...il.com>
> >> ---
> >>   .../admin-guide/kernel-parameters.txt         |  12 +-
> >>   MAINTAINERS                                   |   5 +
> >>   drivers/firmware/efi/Kconfig                  |   6 +-
> >>   drivers/firmware/efi/Makefile                 |   1 -
> >>   drivers/firmware/efi/earlycon.c               | 246 --------------
> >>   drivers/video/fbdev/Kconfig                   |  11 +
> >>   drivers/video/fbdev/Makefile                  |   1 +
> >>   drivers/video/fbdev/earlycon.c                | 301 ++++++++++++++++++
> >
> > It looks like this is not actually related to fbdev, and since drivers are
> > moving from fbdev/simplefb towards drm/simpledrm, maybe it would be
> > better to put this into either drivers/gpu/drm/tiny/ or possibly
> > drivers/video/console to let this be used without enabling fbdev?
>
> Ideally this shouldn't depend on anything, because it isn't utilizing
> any of fbdev code and won't be utilizing any of drm/console code. I
> agree that either of those would be a better place for it, but which one
> do you think would suit more for this driver?

I think ideally this would be integrated with simpledrm in the long run,
but I have no idea what that means in terms of future code changes.

Maybe Thomas Zimmermann has an idea here.

        Arnd