linux-kernel - Re: [PATCH 1/3] drm/simpledrm: Bind to OF framebuffers in /chosen

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Date:   Tue, 30 Nov 2021 12:25:00 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Javier Martinez Canillas <javier@...hile0.org>
Cc:     Hector Martin <marcan@...can.st>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>
Subject: Re: [PATCH 1/3] drm/simpledrm: Bind to OF framebuffers in /chosen

On Tue, Nov 30, 2021 at 12:45 AM Javier Martinez Canillas
<javier@...hile0.org> wrote:
>
> > > >
> > > > Simpledrm is just a driver, but this is platform setup code. Why is this
> > > > code located here and not under arch/ or drivers/firmware/?
> > > >
>
> Agreed. Creating platform devices is something for platform code and
> not really a DRM driver.
>
> > > > I know that other drivers do similar things, it doesn't seem to belong here.
> > >
>
> Yeah, the simplefb driver does this but that seems like something that
> should be changed.
>
> > > This definitely doesn't belong in either of those, since it is not arch-
> > > or firmware-specific. It is implementing support for the standard
> > > simple-framebuffer OF binding, which specifies that it must be located
> > > within the /chosen node (and thus the default OF setup code won't do the
> > > matching for you); this applies to all OF platforms [1]
> > >
> > > Adding Rob; do you think this should move from simplefb/simpledrm to
> > > common OF code? (where?)
> >
> > of_platform_default_populate_init() should work.
>
> That should work but I still wonder if it is the correct place to add
> this logic.

It is because that is where most of the other devices are created
unless the bus handles it.

> I think that instead it could be done in the sysfb_create_simplefb()
> function [0], which already creates the "simple-framebuffer" device
> for x86 legacy BIOS and x86/arm64/riscv EFI so it makes sense to do
> the same for OF. That way the simplefb platform device registration
> code could also be dropped from the driver and users would just need
> to enable CONFIG_SYSFB and CONFIG_SYSFB_SIMPLEFB to have the same.

Doesn't look like that would share anything with anything else (BIOS/EFI/ACPI).

Rob