linux-kernel - Re: [PATCH 3/3] drm/pl111: depend on CONFIG_VEXPRESS

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Date:   Thu, 3 Jun 2021 14:19:52 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     Rob Herring <robh@...nel.org>, Dave Airlie <airlied@...hat.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Arnd Bergmann <arnd@...nel.org>,
        kernel test robot <lkp@...el.com>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Emma Anholt <emma@...olt.net>, Rob Clark <robdclark@...il.com>,
        Sean Paul <sean@...rly.run>,
        Sharat Masetty <smasetty@...eaurora.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>
Subject: Re: [PATCH 3/3] drm/pl111: depend on CONFIG_VEXPRESS_CONFIG

On Thu, Jun 03, 2021 at 09:19:42PM +0200, Daniel Vetter wrote:
> On Thu, Jun 3, 2021 at 8:43 PM Rob Herring <robh@...nel.org> wrote:
> >
> > On Wed, Jun 2, 2021 at 4:53 PM Kees Cook <keescook@...omium.org> wrote:
> > >
> > > Avoid randconfig build failures by requiring VEXPRESS_CONFIG:
> > >
> > > aarch64-linux-gnu-ld: drivers/gpu/drm/pl111/pl111_versatile.o: in function `pl111_vexpress_clcd_init':
> > > pl111_versatile.c:(.text+0x220): undefined reference to `devm_regmap_init_vexpress_config'
> >
> > pl111_vexpress_clcd_init() starts with:
> >
> > if (!IS_ENABLED(CONFIG_VEXPRESS_CONFIG))
> >                 return -ENODEV;
> >
> > Isn't that supposed to be enough to avoid an undefined reference?

Ah! I missed that when reading the code. I see the problem now. It's
because of:

CONFIG_VEXPRESS_CONFIG=m
CONFIG_DRM_PL111=y

I think the right fix is:

diff --git a/drivers/gpu/drm/pl111/Kconfig b/drivers/gpu/drm/pl111/Kconfig
index 80f6748055e3..662fc38f92ba 100644
--- a/drivers/gpu/drm/pl111/Kconfig
+++ b/drivers/gpu/drm/pl111/Kconfig
@@ -3,6 +3,7 @@ config DRM_PL111
 	tristate "DRM Support for PL111 CLCD Controller"
 	depends on DRM
 	depends on ARM || ARM64 || COMPILE_TEST
+	depends on VEXPRESS_CONFIG=y || VEXPRESS_CONFIG=DRM
 	depends on COMMON_CLK
 	select DRM_KMS_HELPER
 	select DRM_KMS_CMA_HELPER

I will go check the defconfigs Rob mentioned...

> > Making the whole file depend on VEXPRESS_CONFIG is not right either.
> > Not all platforms need it.
> 
> It needs a compile-time status inline then for the functions we're
> using in pl111.

FYI, this is the config I was working from, which was throwing link errors:
https://lore.kernel.org/lkml/202105300926.fX0MYySp-lkp@intel.com/

> -Daniel
> 
> >
> > >
> > > Fixes: 826fc86b5903 ("drm: pl111: Move VExpress setup into versatile init")
> > > Signed-off-by: Kees Cook <keescook@...omium.org>
> > > ---
> > >  drivers/gpu/drm/pl111/Kconfig | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/pl111/Kconfig b/drivers/gpu/drm/pl111/Kconfig
> > > index 80f6748055e3..c5210a5bef1b 100644
> > > --- a/drivers/gpu/drm/pl111/Kconfig
> > > +++ b/drivers/gpu/drm/pl111/Kconfig
> > > @@ -2,7 +2,7 @@
> > >  config DRM_PL111
> > >         tristate "DRM Support for PL111 CLCD Controller"
> > >         depends on DRM
> > > -       depends on ARM || ARM64 || COMPILE_TEST
> > > +       depends on VEXPRESS_CONFIG
> > >         depends on COMMON_CLK
> > >         select DRM_KMS_HELPER
> > >         select DRM_KMS_CMA_HELPER
> > > --
> > > 2.25.1
> > >
> 
> 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Kees Cook