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Date:   Mon, 18 May 2020 14:09:29 +0800
From:   Zhenyu Wang <zhenyuw@linux.intel.com>
To:     Nathan Chancellor <natechancellor@gmail.com>
Cc:     Zhenyu Wang <zhenyuw@linux.intel.com>,
        Zhi Wang <zhi.a.wang@intel.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org,
        clang-built-linux@googlegroups.com,
        intel-gvt-dev@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915: Mark check_shadow_context_ppgtt as maybe unused
Message-ID: <20200518060929.GS18545@zhen-hp.sh.intel.com>
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On 2020.05.15 19:35:45 -0700, Nathan Chancellor wrote:
> When CONFIG_DRM_I915_DEBUG_GEM is not set, clang warns:
>=20
> drivers/gpu/drm/i915/gvt/scheduler.c:884:1: warning: function
> 'check_shadow_context_ppgtt' is not needed and will not be emitted
> [-Wunneeded-internal-declaration]
> check_shadow_context_ppgtt(struct execlist_ring_context *c, struct
> intel_vgpu_mm *m)
> ^
> 1 warning generated.
>=20
> This warning is similar to -Wunused-function but rather than warning
> that the function is completely unused, it warns that it is used in some
> expression within the file but that expression will be evaluated to a
> constant or be optimized away in the final assembly, essentially making
> it appeared used but really isn't. Usually, this happens when a function
> or variable is only used in sizeof, where it will appear to be used but
> will be evaluated at compile time and not be required to be emitted.
>=20
> In this case, the function is only used in GEM_BUG_ON, which is defined
> as BUILD_BUG_ON_INVALID, which intentionally follows this pattern. To
> fix this warning, add __maybe_unused to make it clear that this is
> intentional depending on the configuration.
>=20
> Fixes: bec3df930fbd ("drm/i915/gvt: Support PPGTT table load command")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1027
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>  drivers/gpu/drm/i915/gvt/scheduler.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>=20
> diff --git a/drivers/gpu/drm/i915/gvt/scheduler.c b/drivers/gpu/drm/i915/=
gvt/scheduler.c
> index f776c92de8d7..0fb1df71c637 100644
> --- a/drivers/gpu/drm/i915/gvt/scheduler.c
> +++ b/drivers/gpu/drm/i915/gvt/scheduler.c
> @@ -880,7 +880,7 @@ static void update_guest_pdps(struct intel_vgpu *vgpu,
>  				gpa + i * 8, &pdp[7 - i], 4);
>  }
> =20
> -static bool
> +static __maybe_unused bool
>  check_shadow_context_ppgtt(struct execlist_ring_context *c, struct intel=
_vgpu_mm *m)
>  {
>  	if (m->ppgtt_mm.root_entry_type =3D=3D GTT_TYPE_PPGTT_ROOT_L4_ENTRY) {
>=20
> base-commit: bdecf38f228bcca73b31ada98b5b7ba1215eb9c9

Thanks for the fix!

Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com>

I'll pick up for gvt-next-fixes pull.

--=20
Open Source Technology Center, Intel ltd.

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