linux-kernel - Re: [PATCH] drm/bridge: fix RC

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Message-ID: <CAKdAkRQQn40nUm6KjK80Zj95b_dhkTmETp7rMe+1s61gR4Xv5Q@mail.gmail.com>
Date:   Thu, 18 Jul 2019 18:13:08 +0300
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Andrzej Hajda <a.hajda@...sung.com>
Cc:     Arnd Bergmann <arnd@...db.de>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Ronald Tschalär <ronald@...ovation.ch>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Sean Paul <sean@...rly.run>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/bridge: fix RC_CORE dependency

On Thu, Jul 18, 2019 at 5:55 PM Andrzej Hajda <a.hajda@...sung.com> wrote:
>
> On 18.07.2019 16:21, Arnd Bergmann wrote:
> > On Thu, Jul 18, 2019 at 4:16 PM Andrzej Hajda <a.hajda@...sung.com> wrote:
> >> Hi Arnd,
> >>
> >> 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:
> >>>
> >>> drivers/media/rc/rc-main.o: In function `ir_do_keyup':
> >>> rc-main.c:(.text+0x2b4): undefined reference to `input_event'
> >>> drivers/media/rc/rc-main.o: In function `rc_repeat':
> >>> rc-main.c:(.text+0x350): undefined reference to `input_event'
> >>> drivers/media/rc/rc-main.o: In function `rc_allocate_device':
> >>> rc-main.c:(.text+0x90c): undefined reference to `input_allocate_device'
> >>>
> >>> Add a 'depends on' that allows building both with and without
> >>> CONFIG_RC_CORE, but disallows combinations that don't link.
> >>>
> >>> Fixes: 5023cf32210d ("drm/bridge: make remote control optional")
> >>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> >>
> >> Proper solution has been already merged via input tree[1].
> >>
> >>
> >> [1]:
> >> https://lore.kernel.org/lkml/CAKdAkRTGXNbUsuKASNGLfwUwC7Asod9K5baYLPWPU7EX-42-yA@mail.gmail.com/
> > At that link, I only see the patch that caused the regression, not
> > the solution. Are you sure it's fixed?
>
>
> Ups, you are right, I though you are fixing what this patch attempted to
> fix :)
>
> Anyway, we want to avoid dependency on RC_CORE - this driver does not
> require it, but with RC_CORE it has additional features.
>
> Maybe "imply INPUT" would help?

No, it won't. I am sorry, I should have looked closer, but as written,
drivers/gpu/drm/bridge/sil-sii8620.c has a hard dependency on the RC
core and "imply" was the wrong solution for this, we need "depends on
RC_CORE". If we want to make RC support optional than we should stub
out paths that use RC_CORE (such as sii8620_init_rcp_input_dev()) and
guard them by "#ifdef CONFIG_RC_CORE". Then we could keep "imply" on
RC_CORE.

I am surprised though that imply allows violating the constraint on
implied symbols, as RC_CORE has straight "depends on" for INPUT.

Thanks.

-- 
Dmitry