linux-kernel - Re: [PATCH 5.15 808/917] drm: fb_helper: improve CONFIG

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Message-ID: <CAK8P3a0W+U=82dGWZS7vSoGbnB+wmVVckSM2ppZyk_szhTYE+g@mail.gmail.com>
Date:   Fri, 19 Nov 2021 10:33:38 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     "Alan J. Wylie" <alan@...ie.me.uk>
Cc:     Arnd Bergmann <arnd@...db.de>, Jiri Slaby <jirislaby@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "# 3.4.x" <stable@...r.kernel.org>,
        "Acked-by: Jani Nikula" <jani.nikula@...el.com>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.15 808/917] drm: fb_helper: improve CONFIG_FB dependency

On Fri, Nov 19, 2021 at 9:57 AM Alan J. Wylie <alan@...ie.me.uk> wrote:
>
>
> Arnd Bergmann <arnd@...db.de> writes:
>
> > Ah right, I ran into a similar thing on my randconfig builds, this is
> > what I have
> > applied locally but wasn't completely sure about yet, it may need additional
> > 'select DRM_KMS_CMA_HELPER' to cover all instances:
>
> With 5.15.3, I had these errors on *one* of my boxes with Nvidia
> drivers when building the nvidia drivers
>
> Gentoo, nvidia-drivers-470.86
>
> ERROR: modpost: "drm_atomic_helper_update_plane" [/work/tmp/portage/x11-drivers/nvidia-drivers-470.86/work/kernel/nvidia-drm.ko] undefined!
> ERROR: modpost: "drm_atomic_helper_connector_reset" [/work/tmp/portage/x11-drivers/nvidia-drivers-470.86/work/kernel/nvidia-drm.ko] undefined!
> ERROR: modpost: "drm_atomic_helper_page_flip" [/work/tmp/portage/x11-drivers/nvidia-drivers-470.86/work/kernel/nvidia-drm.ko]

To be honest, I'm not overly stressed out about breaking external
modules. It is true that this driver only builds when CONFIG_DRM_KMS_HELPER
is set, so you end up having to enable some other driver that selects
it because the kernel doesn't know what symbols would be used.
If you enable CONFIG_TRIM_UNUSED_KSYMS, you'd likely get additional
problems here.

Before my patch, the kms helpers were selected by
CONFIG_DRM_FBDEV_EMULATION in your .config, but this made no
sense unless you also have a third-party module that uses it.

         Arnd