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Date:   Fri, 7 Jul 2023 13:47:09 +0200
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Subject: Re: [PATCH] [v2] drm/amdgpu: avoid integer overflow warning in
 amdgpu_device_resize_fb_bar()
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To:     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>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Hawking Zhang <Hawking.Zhang@amd.com>,
        Lijo Lazar <lijo.lazar@amd.com>,
        Mario Limonciello <mario.limonciello@amd.com>,
        YiPeng Chai <YiPeng.Chai@amd.com>, Le Ma <le.ma@amd.com>,
        Bokun Zhang <Bokun.Zhang@amd.com>,
        Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>,
        Shiwu Zhang <shiwu.zhang@amd.com>,
        amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
References: <20230707111157.209432-1-arnd@kernel.org>
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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 than
> U32_MAX can cause a warning:
>
> drivers/gpu/drm/amd/amdgpu/amdgpu_device.c:1344:18: error: result of comparison 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 actually resize
> the BAR on 32-bit architectures without high memory, which is exactly what
> 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 König <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/drm/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_device *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;