drm/amdgpu: limit visible vram if it's smaller than the BAR

BugLink: http://bugs.launchpad.net/bugs/1546572

In some cases the amount of vram may be less than the BAR size,
if so, limit visible vram to the amount of actual vram, not the
BAR size.
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit a1493cd5)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c

@@ -407,6 +407,10 @@ static int gmc_v7_0_mc_init(struct amdgpu_device *adev)
 	adev->mc.real_vram_size = RREG32(mmCONFIG_MEMSIZE) * 1024ULL * 1024ULL;
 	adev->mc.visible_vram_size = adev->mc.aper_size;
 
+	/* In case the PCI BAR is larger than the actual amount of vram */
+	if (adev->mc.visible_vram_size > adev->mc.real_vram_size)
+		adev->mc.visible_vram_size = adev->mc.real_vram_size;
+
 	/* unless the user had overridden it, set the gart
 	 * size equal to the 1024 or vram, whichever is larger.
 	 */

drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c

@@ -448,6 +448,10 @@ static int gmc_v8_0_mc_init(struct amdgpu_device *adev)
 	adev->mc.real_vram_size = RREG32(mmCONFIG_MEMSIZE) * 1024ULL * 1024ULL;
 	adev->mc.visible_vram_size = adev->mc.aper_size;
 
+	/* In case the PCI BAR is larger than the actual amount of vram */
+	if (adev->mc.visible_vram_size > adev->mc.real_vram_size)
+		adev->mc.visible_vram_size = adev->mc.real_vram_size;
+
 	/* unless the user had overridden it, set the gart
 	 * size equal to the 1024 or vram, whichever is larger.
 	 */