linux-kernel - Re: [PATCH] drm/amdgpu: avoid integer overflow warning in amdgpu_device_resize_fb

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Date:   Tue, 4 Jul 2023 08:54:03 +0200
From:   Christian König <christian.koenig@....com>
To:     Arnd Bergmann <arnd@...nel.org>,
        Alex Deucher <alexander.deucher@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Hawking Zhang <Hawking.Zhang@....com>,
        Lijo Lazar <lijo.lazar@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        YiPeng Chai <YiPeng.Chai@....com>, Le Ma <le.ma@....com>,
        Bokun Zhang <Bokun.Zhang@....com>,
        Srinivasan Shanmugam <srinivasan.shanmugam@....com>,
        Shiwu Zhang <shiwu.zhang@....com>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/amdgpu: avoid integer overflow warning in
 amdgpu_device_resize_fb_bar()

Am 03.07.23 um 14:35 schrieb Arnd Bergmann:
> From: Arnd Bergmann <arnd@...db.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)
>                      ~~~~~~~~~~ ^ ~~~~~~~~~~~~~~
>
> The compiler is right that this cannot happen in this configuration, which
> is ok, so just add a cast to shut up the warning.

Well it doesn't make sense to compile that driver on systems with only 
32bit phys_addr_t in the first place.

It might be cleaner to just not build the whole driver on such systems 
or at least leave out this function.

Regards,
Christian

>
> Fixes: 31b8adab3247e ("drm/amdgpu: require a root bus window above 4GB for BAR resize")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> index 7f069e1731fee..abd13942aac5d 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> @@ -1341,7 +1341,7 @@ int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
>   
>   	pci_bus_for_each_resource(root, res, i) {
>   		if (res && res->flags & (IORESOURCE_MEM | IORESOURCE_MEM_64) &&
> -		    res->start > 0x100000000ull)
> +		    (u64)res->start > 0x100000000ull)
>   			break;
>   	}
>