linux-kernel - Re: [PATCH] drm/fb-helper: don't call remove_conflicting

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Message-ID: <20160829125243.GI10980@phenom.ffwll.local>
Date:   Mon, 29 Aug 2016 14:52:43 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Chris Wilson <chris@...is-wilson.co.uk>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Noralf Trønnes <noralf@...nnes.org>,
        Rob Clark <robdclark@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/fb-helper: don't call
 remove_conflicting_framebuffers for FB=m && DRM=y

On Mon, Aug 29, 2016 at 02:34:07PM +0200, Arnd Bergmann wrote:
> When CONFIG_DRM_KMS_FB_HELPER is disabled, we can have a configuration
> in which some DRM drivers are built-in, but the framebuffer core is a
> loadable module. This results in a link error, such as:
> 
> drivers/gpu/drm/radeon/radeon.o: In function `radeon_pci_probe':
> radeon_kfd.c:(.text.radeon_pci_probe+0xbc): undefined reference to `remove_conflicting_framebuffers'
> drivers/gpu/drm/amd/amdgpu/amdgpu.o: In function `amdgpu_pci_probe':
> amdgpu_mn.c:(.text.amdgpu_pci_probe+0xa8): undefined reference to `remove_conflicting_framebuffers'
> drivers/gpu/drm/mgag200/mgag200.o: In function `mga_vram_init':
> mgag200_ttm.c:(.text.mga_vram_init+0xa8): undefined reference to `remove_conflicting_framebuffers'
> drivers/gpu/drm/mgag200/mgag200.o: In function `mga_pci_probe':
> mgag200_ttm.c:(.text.mga_pci_probe+0x88): undefined reference to `remove_conflicting_framebuffers'
> Makefile:969: recipe for target 'vmlinux' failed
> 
> This changes the compile-time check to IS_REACHABLE, which means we end up
> not calling remove_conflicting_framebuffers() in the configuration, which
> seems good enough, as we know that no framebuffer driver is loaded by the
> time that the built-in DRM driver calls remove_conflicting_framebuffers.
> 
> We could alternatively avoid the link error by forcing CONFIG_FB to not
> be a module in this case, but that wouldn't change anything at runtime,
> and just make the already convoluted set of dependencies worse here.
> 
> I could not find out what happens if the fbdev driver gets loaded as
> a module after the DRM driver is already initialized, but that is a case
> that can happen with or without this patch.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Fixes: 0a3bfe29f816 ("drm/fb-helper: Fix the dummy remove_conflicting_framebuffers")

Applied to drm-misc, thanks.
-Daniel

> ---
>  include/drm/drm_fb_helper.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index edc6cfd3aa34..797fb5f80c45 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -491,7 +491,7 @@ static inline int
>  drm_fb_helper_remove_conflicting_framebuffers(struct apertures_struct *a,
>  					      const char *name, bool primary)
>  {
> -#if IS_ENABLED(CONFIG_FB)
> +#if IS_REACHABLE(CONFIG_FB)
>  	return remove_conflicting_framebuffers(a, name, primary);
>  #else
>  	return 0;
> -- 
> 2.9.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch