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Date:   Thu, 22 Apr 2021 10:58:10 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Arnd Bergmann <arnd@kernel.org>
Cc:     Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Zhenyu Wang <zhenyuw@linux.intel.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Kevin Tian <kevin.tian@intel.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] vfio/gvt: fix DRM_I915_GVT dependency on VFIO_MDEV
Message-ID: <20210422135810.GG2047089@ziepe.ca>
References: <20210422133547.1861063-1-arnd@kernel.org>
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On Thu, Apr 22, 2021 at 03:35:33PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> The Kconfig dependency is incomplete since DRM_I915_GVT is a 'bool'
> symbol that depends on the 'tristate' VFIO_MDEV. This allows a
> configuration with VFIO_MDEV=m, DRM_I915_GVT=y and DRM_I915=y that
> causes a link failure:
> 
> x86_64-linux-ld: drivers/gpu/drm/i915/gvt/gvt.o: in function `available_instances_show':
> gvt.c:(.text+0x67a): undefined reference to `mtype_get_parent_dev'
> x86_64-linux-ld: gvt.c:(.text+0x6a5): undefined reference to `mtype_get_type_group_id'
> x86_64-linux-ld: drivers/gpu/drm/i915/gvt/gvt.o: in function `description_show':
> gvt.c:(.text+0x76e): undefined reference to `mtype_get_parent_dev'
> x86_64-linux-ld: gvt.c:(.text+0x799): undefined reference to `mtype_get_type_group_id'
> 
> Clarify the dependency by specifically disallowing the broken
> configuration. If VFIO_MDEV is built-in, it will work, but if
> VFIO_MDEV=m, the i915 driver cannot be built-in here.
> 
> Fixes: 07e543f4f9d1 ("vfio/gvt: Make DRM_I915_GVT depend on VFIO_MDEV")
> Fixes: 9169cff168ff ("vfio/mdev: Correct the function signatures for the mdev_type_attributes")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/gpu/drm/i915/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Oh kconfig stuff like this makes my head hurt, thanks for finding it

I also can't see an alternative to this ugly thing, besides having the
i915 guys properly modularize this code someday

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason