drm/amdgpu: fix the page fault of raven2

While the apg_end address is 0xffffffff, if add 1 with it, the value will be
overflow and roll back to 0. So when 0 is written to
mmMC_VM_SYSTEM_APERTURE_HIGH_ADDR, the system aperture is actually disabled. And
so any access to vram will trigger a page fault.

Raven2's HW issue only need increase the vram end address, and needn't do it on
the agp.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/gfxhub_v1_0.c

@@ -82,7 +82,8 @@ static void gfxhub_v1_0_init_system_aperture_regs(struct amdgpu_device *adev)
 		 * to get rid of the VM fault and hardware hang.
 		 */
 		WREG32_SOC15(GC, 0, mmMC_VM_SYSTEM_APERTURE_HIGH_ADDR,
-			     (max(adev->gmc.vram_end, adev->gmc.agp_end) >> 18) + 0x1);
+			     max((adev->gmc.vram_end >> 18) + 0x1,
+				 adev->gmc.agp_end >> 18));
 	else
 		WREG32_SOC15(GC, 0, mmMC_VM_SYSTEM_APERTURE_HIGH_ADDR,
 			     max(adev->gmc.vram_end, adev->gmc.agp_end) >> 18);

drivers/gpu/drm/amd/amdgpu/mmhub_v1_0.c

@@ -100,7 +100,8 @@ static void mmhub_v1_0_init_system_aperture_regs(struct amdgpu_device *adev)
 		 * to get rid of the VM fault and hardware hang.
 		 */
 		WREG32_SOC15(MMHUB, 0, mmMC_VM_SYSTEM_APERTURE_HIGH_ADDR,
-			     (max(adev->gmc.vram_end, adev->gmc.agp_end) >> 18) + 0x1);
+			     max((adev->gmc.vram_end >> 18) + 0x1,
+				 adev->gmc.agp_end >> 18));
 	else
 		WREG32_SOC15(MMHUB, 0, mmMC_VM_SYSTEM_APERTURE_HIGH_ADDR,
 			     max(adev->gmc.vram_end, adev->gmc.agp_end) >> 18);