linux-kernel - Re: [PATCH] drm: pl111: add CONFIG_VEXPRESS

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Date:   Wed, 27 May 2020 19:50:12 +0200
From:   Sam Ravnborg <sam@...nborg.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     David Airlie <airlied@...ux.ie>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Alex Deucher <alexander.deucher@....com>
Subject: Re: [PATCH] drm: pl111: add CONFIG_VEXPRESS_CONFIG dependency

Hi Arnd.

On Wed, May 27, 2020 at 05:47:21PM +0200, Arnd Bergmann wrote:
> On Wed, May 27, 2020 at 4:52 PM Sam Ravnborg <sam@...nborg.org> wrote:
> >
> > Hi Arnd.
> >
> > On Wed, May 27, 2020 at 03:31:42PM +0200, Arnd Bergmann wrote:
> > > The vexpress_config code fails to link in some configurations:
> > >
> > > drivers/gpu/drm/pl111/pl111_versatile.o: in function `pl111_versatile_init':
> > > (.text+0x1f0): undefined reference to `devm_regmap_init_vexpress_config'
> > >
> > > Add a dependency that links to this only if the dependency is there,
> > > and prevent the configuration where the drm driver is built-in but
> > > the config is a loadable module.
> > >
> > > Fixes: 826fc86b5903 ("drm: pl111: Move VExpress setup into versatile init")
> > > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> >
> > Could this be another way to fix it:
> >
> > diff --git a/drivers/gpu/drm/pl111/pl111_versatile.c b/drivers/gpu/drm/pl111/pl111_versatile.c
> > index 64f01a4e6767..1c38d3bd2e84 100644
> > --- a/drivers/gpu/drm/pl111/pl111_versatile.c
> > +++ b/drivers/gpu/drm/pl111/pl111_versatile.c
> > @@ -379,7 +379,7 @@ static int pl111_vexpress_clcd_init(struct device *dev, struct device_node *np,
> >         u32 val;
> >         int ret;
> >
> > -       if (!IS_ENABLED(CONFIG_VEXPRESS_CONFIG))
> > +       if (!IS_REACHABLE(CONFIG_VEXPRESS_CONFIG))
> >                 return -ENODEV;
> >
> >         /*
> >
> >
> > Then we no longer have the whole driver depending on
> > the value of VEXPRESS_CONFIG.
> > Not that I like IS_REACHABLE() but we already had
> > IS_ENABLED() to cover up here, and that was not enough.
> >
> > With your patch would we then need the IS_ENABLED()
> > check?
> 
> The IS_ENABLED() check is what I'm adding, not removing. I'd still
> the Kconfig dependency combined with that check over
> IS_REACHABLE(), which is more likely to silently not work.

Then the now redundant IS_ENABLED() check should go.
With you patch it looks like this:

	...
	if (IS_ENABLED(CONFIG_VEXPRESS_CONFIG) && ...)
		pl111_vexpress_clcd_init()


And in pl111_vexpress_clcd_init() we have:

{
	if (!IS_ENABLED(CONFIG_VEXPRESS_CONFIG))
		return -ENODEV;

The IS_ENABLED() in pl111_vexpress_clcd_init() is redundant
and the patch should drop it.

	Sam