linux-kernel - Re: [PATCH v2] drm/bridge/sii8620: fix dependency on extcon

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Message-ID: <CAG3jFys1xF9qrhDziUNm9fY8uDY0LSt6xvsnNohY7z0Qp6hMaQ@mail.gmail.com>
Date:   Tue, 13 Apr 2021 19:02:14 +0200
From:   Robert Foss <robert.foss@...aro.org>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v2] drm/bridge/sii8620: fix dependency on extcon

Hey Randy,

Thanks for looking at this!

On Fri, 9 Apr 2021 at 18:38, Randy Dunlap <rdunlap@...radead.org> wrote:
>
> On 4/8/21 6:07 AM, Robert Foss wrote:
> > The DRM_SIL_SII8620 kconfig has a weak `imply` dependency
> > on EXTCON, which causes issues when sii8620 is built
> > as a builtin and EXTCON is built as a module.
> >
> > The symptoms are 'undefined reference' errors caused
> > by the symbols in EXTCON not being available
> > to the sii8620 driver.
> >
> > Signed-off-by: Robert Foss <robert.foss@...aro.org>
> > Reported-by: kernel test robot <lkp@...el.com>
> > ---
> >
> > Changes since v1:
> >  - Fix typo on comment
> >
> >  drivers/gpu/drm/bridge/Kconfig | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> > index 22a467abd3e9..2289b44613af 100644
> > --- a/drivers/gpu/drm/bridge/Kconfig
> > +++ b/drivers/gpu/drm/bridge/Kconfig
> > @@ -169,7 +169,7 @@ config DRM_SIL_SII8620
> >       tristate "Silicon Image SII8620 HDMI/MHL bridge"
> >       depends on OF
> >       select DRM_KMS_HELPER
> > -     imply EXTCON
> > +     depends on EXTCON || !EXTCON # if EXTCON=m, this cannot be built-in
> >       depends on RC_CORE || !RC_CORE
> >       help
> >         Silicon Image SII8620 HDMI/MHL bridge chip driver.
> >
>
> That gives me: (on linux-next 20210409)
>
> drivers/gpu/drm/Kconfig:77:error: recursive dependency detected!
> drivers/gpu/drm/Kconfig:77:     symbol DRM_KMS_HELPER is selected by DRM_SIL_SII8620
> drivers/gpu/drm/bridge/Kconfig:168:     symbol DRM_SIL_SII8620 depends on EXTCON
> drivers/extcon/Kconfig:2:       symbol EXTCON is selected by CHARGER_MANAGER
> drivers/power/supply/Kconfig:499:       symbol CHARGER_MANAGER depends on POWER_SUPPLY
> drivers/power/supply/Kconfig:2: symbol POWER_SUPPLY is selected by OLPC_XO1_SCI
> arch/x86/Kconfig:2757:  symbol OLPC_XO1_SCI depends on GPIO_CS5535
> drivers/gpio/Kconfig:1156:      symbol GPIO_CS5535 depends on GPIOLIB
> drivers/gpio/Kconfig:14:        symbol GPIOLIB is selected by I2C_MUX_LTC4306
> drivers/i2c/muxes/Kconfig:47:   symbol I2C_MUX_LTC4306 depends on I2C
> drivers/i2c/Kconfig:8:  symbol I2C is selected by FB_DDC
> drivers/video/fbdev/Kconfig:63: symbol FB_DDC depends on FB
> drivers/video/fbdev/Kconfig:12: symbol FB is selected by DRM_KMS_FB_HELPER
> drivers/gpu/drm/Kconfig:83:     symbol DRM_KMS_FB_HELPER depends on DRM_KMS_HELPER
> For a resolution refer to Documentation/kbuild/kconfig-language.rst
> subsection "Kconfig recursive dependency limitations"

I'm not sure how to avoid this circular dependency. The above solution
is what I've seen w/r to issues like [1]. Clearly it doesn't work in
this situation. `select EXTCON` doesn't seem to cause this dependency
error, but I'm not sure it accurately represents the dependency
sii8620 has on extcon.

[1] https://lore.kernel.org/lkml/202104040604.SSTe2Cxf-lkp@intel.com/