[PATCH 8/8] vfio/igd: add x-igd-gms option back to set DSM region size for guest

[Tomita Moeko]

DSM region is likely to store framebuffer in Windows, a small DSM
region may cause display issues (e.g. half of the screen is black).
By default, QEMU uses host's original value, which is determined by
DVMT Pre-Allocated option in Intel FSP of host bios. Some vendors
do not expose this config item to users. In such cases, x-igd-gms
option can be used to manually set the data stolen memory size for
guest.

When DVMT Pre-Allocated option is available in host BIOS, user should
set DSM region size there instead of using x-igd-gms option.

Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
---
 hw/vfio/igd.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/hw/vfio/igd.c b/hw/vfio/igd.c
index 3fd822241d..614223123b 100644
--- a/hw/vfio/igd.c
+++ b/hw/vfio/igd.c
@@ -712,6 +712,23 @@ void vfio_probe_igd_bar4_quirk(VFIOPCIDevice *vdev, int nr)
 
     QLIST_INSERT_HEAD(&vdev->bars[nr].quirks, quirk, next);
 
+    /*
+     * Allow user to override dsm size using x-igd-gms option, in multiples of
+     * 32MiB. This option should only be used when the desired size cannot be
+     * set from DVMT Pre-Allocated option in host BIOS.
+     */
+    if (vdev->igd_gms) {
+        if (gen < 8 && vdev->igd_gms <= 0x10) {
+            gmch &= ~(IGD_GMCH_GEN6_GMS_MASK << IGD_GMCH_GEN6_GMS_SHIFT);
+            gmch |= vdev->igd_gms << IGD_GMCH_GEN6_GMS_SHIFT;
+        } else if (vdev->igd_gms <= 0x40) {
+            gmch &= ~(IGD_GMCH_GEN8_GMS_MASK << IGD_GMCH_GEN8_GMS_SHIFT);
+            gmch |= vdev->igd_gms << IGD_GMCH_GEN8_GMS_SHIFT;
+        } else {
+            error_report("Unsupported IGD GMS value 0x%x", vdev->igd_gms);
+        }
+    }
+
     ggms_size = igd_gtt_memory_size(gen, gmch);
     gms_size = igd_stolen_memory_size(gen, gmch);
 
-- 
2.45.2