drm/amd/display: properly handling AGP aperture in vm setup

Take into account whether or not the AGP aperture is
enabled or not when calculating the system aperture.

Fixes white screens with DCN 3.1.4.

Based on a patch from Yifan Zhang <yifan1.zhang@amd.com>

Cc: Yifan Zhang <yifan1.zhang@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Yifan Zhang <yifan1.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -1185,24 +1185,38 @@ static void mmhub_read_system_context(struct amdgpu_device *adev, struct dc_phy_
 
 	memset(pa_config, 0, sizeof(*pa_config));
 
-	logical_addr_low  = min(adev->gmc.fb_start, adev->gmc.agp_start) >> 18;
-	pt_base = amdgpu_gmc_pd_addr(adev->gart.bo);
-
-	if (adev->apu_flags & AMD_APU_IS_RAVEN2)
-		/*
-		 * Raven2 has a HW issue that it is unable to use the vram which
-		 * is out of MC_VM_SYSTEM_APERTURE_HIGH_ADDR. So here is the
-		 * workaround that increase system aperture high address (add 1)
-		 * to get rid of the VM fault and hardware hang.
-		 */
-		logical_addr_high = max((adev->gmc.fb_end >> 18) + 0x1, adev->gmc.agp_end >> 18);
-	else
-		logical_addr_high = max(adev->gmc.fb_end, adev->gmc.agp_end) >> 18;
-
 	agp_base = 0;
 	agp_bot = adev->gmc.agp_start >> 24;
 	agp_top = adev->gmc.agp_end >> 24;
 
+	/* AGP aperture is disabled */
+	if (agp_bot == agp_top) {
+		logical_addr_low  = adev->gmc.vram_start >> 18;
+		if (adev->apu_flags & AMD_APU_IS_RAVEN2)
+			/*
+			 * Raven2 has a HW issue that it is unable to use the vram which
+			 * is out of MC_VM_SYSTEM_APERTURE_HIGH_ADDR. So here is the
+			 * workaround that increase system aperture high address (add 1)
+			 * to get rid of the VM fault and hardware hang.
+			 */
+			logical_addr_high = (adev->gmc.fb_end >> 18) + 0x1;
+		else
+			logical_addr_high = adev->gmc.vram_end >> 18;
+	} else {
+		logical_addr_low  = min(adev->gmc.fb_start, adev->gmc.agp_start) >> 18;
+		if (adev->apu_flags & AMD_APU_IS_RAVEN2)
+			/*
+			 * Raven2 has a HW issue that it is unable to use the vram which
+			 * is out of MC_VM_SYSTEM_APERTURE_HIGH_ADDR. So here is the
+			 * workaround that increase system aperture high address (add 1)
+			 * to get rid of the VM fault and hardware hang.
+			 */
+			logical_addr_high = max((adev->gmc.fb_end >> 18) + 0x1, adev->gmc.agp_end >> 18);
+		else
+			logical_addr_high = max(adev->gmc.fb_end, adev->gmc.agp_end) >> 18;
+	}
+
+	pt_base = amdgpu_gmc_pd_addr(adev->gart.bo);
 
 	page_table_start.high_part = (u32)(adev->gmc.gart_start >> 44) & 0xF;
 	page_table_start.low_part = (u32)(adev->gmc.gart_start >> 12);