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From:   Arnd Bergmann <arnd@kernel.org>
To:     Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@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
Subject: [PATCH] [v2] drm/amdgpu: avoid integer overflow warning in amdgpu_device_resize_fb_bar()
Date:   Fri,  7 Jul 2023 13:11:51 +0200
Message-Id: <20230707111157.209432-1-arnd@kernel.org>
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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>
---
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;
-- 
2.39.2