pci-host: designware: Limit value range of iATU viewport register

The latest version of qemu (v8.2.0-869-g7a1dc45af5) crashes when booting
the mcimx7d-sabre emulation with Linux v5.11 and later.

qemu-system-arm: ../system/memory.c:2750: memory_region_set_alias_offset: Assertion `mr->alias' failed.

Problem is that the Designware PCIe emulation accepts the full value range
for the iATU Viewport Register. However, both hardware and emulation only
support four inbound and four outbound viewports.

The Linux kernel determines the number of supported viewports by writing
0xff into the viewport register and reading the value back. The expected
value when reading the register is the highest supported viewport index.
Match that code by masking the supported viewport value range when the
register is written. With this change, the Linux kernel reports

imx6q-pcie 33800000.pcie: iATU: unroll F, 4 ob, 4 ib, align 0K, limit 4G

as expected and supported.

Fixes: d64e5ea ("pci: Add support for Designware IP block")
Cc: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Nikita Ostrenkov <n.ostrenkov@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Message-id: 20240129060055.2616989-1-linux@roeck-us.net
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/pci-host/designware.c

@@ -340,6 +340,8 @@ static void designware_pcie_root_config_write(PCIDevice *d, uint32_t address,
         break;
 
     case DESIGNWARE_PCIE_ATU_VIEWPORT:
+        val &= DESIGNWARE_PCIE_ATU_REGION_INBOUND |
+                (DESIGNWARE_PCIE_NUM_VIEWPORTS - 1);
         root->atu_viewport = val;
         break;