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From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Fri, 7 Jul 2023 14:40:37 -0400
Message-ID: <CADnq5_M5KE_woBVfsmVhQPzc4YJon_5mKKuQ72mCnKqU-SdumQ@mail.gmail.com>
Subject: Re: [PATCH] [v2] drm/amdgpu: avoid integer overflow warning in amdgpu_device_resize_fb_bar()
To:     =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>
Cc:     Arnd Bergmann <arnd@kernel.org>,
        Alex Deucher <alexander.deucher@amd.com>,
        "Pan, Xinhui" <Xinhui.Pan@amd.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>, amd-gfx@lists.freedesktop.org,
        Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Bokun Zhang <Bokun.Zhang@amd.com>,
        dri-devel@lists.freedesktop.org, Lijo Lazar <lijo.lazar@amd.com>,
        linux-kernel@vger.kernel.org, Shiwu Zhang <shiwu.zhang@amd.com>,
        Le Ma <le.ma@amd.com>, YiPeng Chai <YiPeng.Chai@amd.com>,
        Mario Limonciello <mario.limonciello@amd.com>,
        Hawking Zhang <Hawking.Zhang@amd.com>
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Applied.  thanks!

On Fri, Jul 7, 2023 at 7:47=E2=80=AFAM Christian K=C3=B6nig <christian.koen=
ig@amd.com> wrote:
>
> Am 07.07.23 um 13:11 schrieb Arnd Bergmann:
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > On 32-bit architectures comparing a resource against a value larger tha=
n
> > U32_MAX can cause a warning:
> >
> > drivers/gpu/drm/amd/amdgpu/amdgpu_device.c:1344:18: error: result of co=
mparison of constant 4294967296 with expression of type 'resource_size_t' (=
aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of=
-range-compare]
> >                      res->start > 0x100000000ull)
> >                      ~~~~~~~~~~ ^ ~~~~~~~~~~~~~~
> >
> > As gcc does not warn about this in dead code, add an IS_ENABLED() check=
 at
> > the start of the function. This will always return success but not actu=
ally resize
> > the BAR on 32-bit architectures without high memory, which is exactly w=
hat
> > we want here, as the driver can fall back to bank switching the VRAM
> > access.
> >
> > Fixes: 31b8adab3247e ("drm/amdgpu: require a root bus window above 4GB =
for BAR resize")
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> Reviewed-by: Christian K=C3=B6nig <christian.koenig@amd.com>
>
> > ---
> > v2: return early instead of shutting up the warning with a cast and
> > running into a failure
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/d=
rm/amd/amdgpu/amdgpu_device.c
> > index 7f069e1731fee..fcf5f07c47751 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> > @@ -1325,6 +1325,9 @@ int amdgpu_device_resize_fb_bar(struct amdgpu_dev=
ice *adev)
> >       u16 cmd;
> >       int r;
> >
> > +     if (!IS_ENABLED(CONFIG_PHYS_ADDR_T_64BIT))
> > +             return 0;
> > +
> >       /* Bypass for VF */
> >       if (amdgpu_sriov_vf(adev))
> >               return 0;
>