Re: [PATCH] drm/bridge: fix RC_CORE dependency

From: Andrzej Hajda <a.hajda@samsung.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: "David Airlie" <airlied@linux.ie>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Ronald Tschalär" <ronald@innovation.ch>,
	"Dmitry Torokhov" <dmitry.torokhov@gmail.com>,
	"Laurent Pinchart" <Laurent.pinchart@ideasonboard.com>,
	"Sean Paul" <sean@poorly.run>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] drm/bridge: fix RC_CORE dependency
Date: Fri, 19 Jul 2019 11:50:35 +0200	[thread overview]
Message-ID: <0a78f32d-009c-fe89-8211-cf5d893d0014@samsung.com> (raw)
In-Reply-To: <CAK8P3a2rJ1WqWZ8VtOZZ5YwFrg5bpVve_kS4utL0MjeBUzrLew@mail.gmail.com>

On 19.07.2019 10:33, Arnd Bergmann wrote:
> On Fri, Jul 19, 2019 at 9:01 AM Andrzej Hajda <a.hajda@samsung.com> wrote:
>> On 18.07.2019 15:42, Arnd Bergmann wrote:
>>> Using 'imply' causes a new problem, as it allows the case of
>>> CONFIG_INPUT=m with RC_CORE=y, which fails to link:
>>
>> I have reviewed dependencies and I wonder how such configuration is
>> possible at all.
>>
>> RC_CORE depends on INPUT (at least on today's next branch) so if INPUT=m
>> then RC_CORE should be either n either m, am I right?
> Right.
>
>> Arnd, are there unknown to me changes in RC/INPUT dependencies?
> I think this is 'imply' behaving oddly when we have conflicting requirements:
>
> - INPUT=m forces RC_CORE to be =m or =n
> - DRM_SIL_SII8620=y asks RC_CORE to be =y unless it cannot be enabled
>
> Kconfig decided to make this RC_CORE=y, which caused the link
> failure. Making it RC_CORE=m however would not work either because
> then we'd get a link failure from the sii8620 driver to rc_core.
>
> so a pure 'imply' cannot work here, and we need a dependency, one of:
>
> a)
>    depends on INPUT || !INPUT
>    select RC_CORE if INPUT
>
> b) depends on RC_CORE || !RC_CORE
>
> b) is what othe drivers use, e.g. SMS_SDIO_DRV

OK, thanks for explanation, really weird.

I though about imply as "weak dependency", but it is "weak select" with
drawbacks of select.

Anyway I am surprised that Kconfig did not complain about contradictory
requirements on RC_CORE symbol.

Regards

Andrzej

>
>        Arnd
>