linux-kernel - Re: [PATCH] drm/amdkfd: fix build error with missing AMD_IOMMU

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Date:   Mon, 8 Mar 2021 20:33:34 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Felix Kuehling <felix.kuehling@....com>
Cc:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Oded Gabbay <oded.gabbay@...il.com>,
        Colin Ian King <colin.king@...onical.com>,
        Philip Yang <philip.yang@....com>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/amdkfd: fix build error with missing AMD_IOMMU_V2

On Mon, Mar 8, 2021 at 8:11 PM Felix Kuehling <felix.kuehling@....com> wrote:
>
> Am 2021-03-08 um 2:05 p.m. schrieb Arnd Bergmann:
> > On Mon, Mar 8, 2021 at 5:24 PM Felix Kuehling <felix.kuehling@....com> wrote:
> >> The driver build should work without IOMMUv2. In amdkfd/Makefile, we
> >> have this condition:
> >>
> >> ifneq ($(CONFIG_AMD_IOMMU_V2),)
> >> AMDKFD_FILES += $(AMDKFD_PATH)/kfd_iommu.o
> >> endif
> >>
> >> In amdkfd/kfd_iommu.h we define inline stubs of the functions that are
> >> causing your link-failures if IOMMU_V2 is not enabled:
> >>
> >> #if defined(CONFIG_AMD_IOMMU_V2_MODULE) || defined(CONFIG_AMD_IOMMU_V2)
> >> ... function declarations ...
> >> #else
> >> ... stubs ...
> >> #endif
> > Right, that is the problem I tried to explain in my patch description.
> >
> > Should we just drop the 'imply' then and add a proper dependency like this?
> >
> >       depends on DRM_AMDGPU && (X86_64 || ARM64 || PPC64)
> >       depends on AMD_IOMMU_V2=y || DRM_AMDGPU=m
> >
> > I can send a v2 after some testing if you prefer this version.
>
> No. My point is, there should not be a hard dependency. The build should
> work without CONFIG_AMD_IOMMU_V2. I don't understand why it's not
> working for you. It looks like you're building kfd_iommu.o, which should
> not be happening when AMD_IOMMU_V2 is not enabled. The condition in
> amdkfd/Makefile should make sure that kfd_iommu.o doesn't get built with
> your kernel config.

Again, as I explained in the changelog text, AMD_IOMMU_V2 configured as
a loadable module, while AMDGPU is configured as built-in.

The causes a link failure for the vmlinux file, because the linker cannot
resolve addresses of loadable modules at compile time -- they have
not been loaded yet.

      Arnd