linux-kernel - Re: [PATCH] drm/sun4i: fix build failure with CONFIG_DRM_SUN8I

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Date:   Mon, 9 Jul 2018 11:15:24 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Arnd Bergmann <arnd@...db.de>, David Airlie <airlied@...ux.ie>,
        Hans Verkuil <hverkuil@...all.nl>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Jonathan Liu <net147@...il.com>,
        Noralf Trønnes <noralf@...nnes.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/sun4i: fix build failure with
 CONFIG_DRM_SUN8I_MIXER=m

On Mon, Jul 09, 2018 at 04:58:48PM +0800, Chen-Yu Tsai wrote:
> On Mon, Jul 9, 2018 at 4:07 PM, Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> > On Fri, Jul 06, 2018 at 02:45:53PM +0200, Arnd Bergmann wrote:
> >> Having DRM_SUN4I built-in but DRM_SUN8I_MIXER as a loadable module results in
> >> a link error, as we try to access a symbol from the sun8i_tcon_top.ko module:
> >>
> >> ERROR: "sun8i_tcon_top_of_table" [drivers/gpu/drm/sun4i/sun8i-drm-hdmi.ko] undefined!
> >> ERROR: "sun8i_tcon_top_of_table" [drivers/gpu/drm/sun4i/sun4i-drm.ko] undefined!
> >>
> >> This solves the problem by making DRM_SUN8I_MIXER a 'bool' symbol, building
> >> the sun8i_tcon_top module the same way as the core sun4i-drm module whenever
> >> DRM_SUN8I_MIXER is enabled, or not building it at all otherwise.
> >>
> >> Alternatively, we could always build sun8i_tcon_top.ko along with sun4-drm.ko
> >> and detach it from the mixer module, I could not tell which way is more
> >> appropriate here.
> >
> > If that's easily doable, then yeah, that would be the preferred option
> > I guess. Jernej? Chen-Yu? Any opinion on this?
> 
> Yeah, that definitely works for me. Having TCON TOP being part of the core
> sun4i-drm makes more sense. The TCON code will likely call into it later on
> when Jernej adds the encoder muxing code.
> 
> I wonder if we shouldn't just build the whole display engine code, excluding
> downstream encoders (HDMI, DSI, TV) into one module. That would also fix the
> issue that DRM_SUN4I_BACKEND has to be built-in if DRM_SUN4I is built-in.
> That might be overkill though, given that one day we should be able to get
> rid of the frontend check.

We can't really do that (or at least without rewriting a significant
part of the driver), since we can have only one
module_init/module_exit function per module, and we have one
per-hardware block.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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