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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Wed, 29 Nov 2023 11:03:16 +0100
Message-ID: <CAMuHMdUODXACTmrtTuKZPZT8xFVn611kDU+DTTjRE7Hn2zS0Zg@mail.gmail.com>
Subject: Re: [PATCH] drm/imagination: DRM_POWERVR should depend on ARCH_K3
To:     Javier Martinez Canillas <javierm@redhat.com>
Cc:     Maxime Ripard <mripard@kernel.org>,
        Frank Binns <frank.binns@imgtec.com>,
        Donald Robson <donald.robson@imgtec.com>,
        Matt Coster <matt.coster@imgtec.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Sarah Walker <sarah.walker@imgtec.com>,
        Nishanth Menon <nm@ti.com>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Tero Kristo <kristo@kernel.org>, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org
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Hi Javier,

On Wed, Nov 29, 2023 at 10:13 AM Javier Martinez Canillas
<javierm@redhat.com> wrote:
> Geert Uytterhoeven <geert@linux-m68k.org> writes:
> > On Wed, Nov 29, 2023 at 9:35 AM Maxime Ripard <mripard@kernel.org> wrote:
> >> On Tue, Nov 28, 2023 at 08:16:18PM +0100, Geert Uytterhoeven wrote:
> >> > On Tue, Nov 28, 2023 at 8:03 PM Javier Martinez Canillas
> >> > <javierm@redhat.com> wrote:
> >> > > Geert Uytterhoeven <geert+renesas@glider.be> writes:
> >> > > > The Imagination Technologies PowerVR Series 6 GPU is currently only
> >> > > > supported on Texas Instruments K3 AM62x SoCs.  Hence add a dependency on
> >> > > > ARCH_K3, to prevent asking the user about this driver when configuring a
> >> > > > kernel without Texas Instruments K3 Multicore SoC support.
> >> > > >
> >> > > > Fixes: 4babef0708656c54 ("drm/imagination: Add skeleton PowerVR driver")
> >> > > > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> >
> >> > > In any case, I agree with you that restricting to only K3 makes sense.
> >> >
> >> > I am looking forward to adding || SOC_AM33XX || ARCH_RENESAS || ...,
> >> > eventually ;-)
> >>
> >> I disagree. This is to handle a generic IP, just like panfrost, lima, or
> >> etnaviv, and we certaintly don't want to maintain the Kconfig list of
> >> every possible architecture and SoC family it might or might not be
> >> found.
> >
> > While PowerVR is a generic IP, I believe it needs a non-generic
> > firmware, which is currently only available for AM62x SoCs.
> > Once it becomes truly generic, I'm happy to drop all platform
> > dependencies.  Until then, there is no point in asking everyone who
> > configures an arm64 kernel about this driver, unless they also enabled
> > K3 support.
>
> That's true but it will require a Kconfig patch every time that there is a
> design with a different SoC using this generic IP.

It also requires a DT bindings patch, to add a new compatible value,
plus whatever missing properties for SoC integration (e.g. resets).
And a DTS integration patch.
And patches for various on-SoC resources (e.g. clocks).
And perhaps a DRM driver update.

> So when should be added? Once there's an upstream DTS that has a GPU device?
> Once there's a firmware for it in linux-firmware?

It can be added when handling the above.  As all patches should be
tested, the firmware must be available first.

When critical mass is reached, platform dependencies can be dropped.
I do hope that will happen rather sooner than later!

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