Support per-head resolutions with virtio-gpu

In 454f4b0f, we started down the path of supporting separate
configurations per display head (e.g., you have 2 heads - one with
EDID name "AAA" and the other with EDID name "BBB").

In this change, we add resolution to this configuration surface (e.g.,
you have 2 heads - one with resolution 111x222 and the other with
resolution 333x444).

  -display vnc=localhost:0,id=aaa,display=vga,head=0 \
  -display vnc=localhost:1,id=bbb,display=vga,head=1 \
  -device '{"driver":"virtio-vga",
            "max_outputs":2,
            "id":"vga",
            "outputs":[
              {
                 "name":"AAA",
                 "xres":111,
                 "yres":222
              },
              {
                 "name":"BBB",
                 "xres":333,
                 "yres":444
              }
            ]}'

Here is the behavior matrix of the current resolution configuration
surface (xres/yres) with the new resolution configuration surface
(outputs[i].xres/yres).

Note - we use "xres" and "yres" (instead of, say, "width" and "height")
to match analogous virtio_gpu_base_conf.xres/yres.

Case: !(xres || yres) && !(outputs[i].has_xres && outputs[i].has_yres)
Behavior: current behavior - outputs[0] enabled with default xres/yres

Case: (xres || yres) && !(outputs[i].has_xres && outputs[i].has_yres)
Behavior: current behavior - outputs[0] enabled with xres/yres

Case: outputs[i].has_xres && outputs[i].has_yres
Behavior: new behavior - outputs[i] enabled with outputs[i].xres/yres

Case: outputs[i].has_xres != outputs[i].has_yres
Behavior: error

Signed-off-by: Andrew Keesler <ankeesler@google.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20260210123038.2332364-2-ankeesler@google.com>
[AJB: fix format strings for size_t in error_setg]
Message-ID: <20260304165043.1437519-2-alex.bennee@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

hw/display/virtio-gpu-base.c

@@ -233,6 +233,22 @@ virtio_gpu_base_device_realize(DeviceState *qdev,
     g->req_state[0].width = g->conf.xres;
     g->req_state[0].height = g->conf.yres;
 
+    for (output_idx = 0, node = g->conf.outputs;
+         node && output_idx < g->conf.max_outputs;
+         output_idx++, node = node->next) {
+        if (node->value->has_xres != node->value->has_yres) {
+            error_setg(errp,
+                       "must set both outputs[%zd].xres and outputs[%zd].yres",
+                       output_idx, output_idx);
+            return false;
+        }
+        if (node->value->has_xres && node->value->has_yres) {
+            g->enabled_output_bitmask |= (1 << output_idx);
+            g->req_state[output_idx].width = node->value->xres;
+            g->req_state[output_idx].height = node->value->yres;
+        }
+    }
+
     g->hw_ops = &virtio_gpu_ops;
     for (i = 0; i < g->conf.max_outputs; i++) {
         g->scanout[i].con =

qapi/virtio.json

@@ -970,15 +970,24 @@
 ##
 # @VirtIOGPUOutput:
 #
-# Describes configuration of a VirtIO GPU output.
+# Describes configuration of a VirtIO GPU output.  If both @xres and
+# @yres are set, they take precedence over root virtio-gpu resolution
+# configuration and enable the corresponding output.  If none of @xres
+# and @yres are set, root virtio-gpu resolution configuration takes
+# precedence and only the first output is enabled.  Only setting one
+# of @xres or @yres is an error.
 #
 # @name: the name of the output
 #
+# @xres: horizontal resolution of the output in pixels (since 11.0)
+#
+# @yres: vertical resolution of the output in pixels (since 11.0)
+#
 # Since: 10.1
 ##
 
 { 'struct': 'VirtIOGPUOutput',
-  'data': { 'name': 'str' } }
+  'data': { 'name': 'str', '*xres': 'uint16', '*yres': 'uint16' } }
 
 ##
 # @DummyVirtioForceArrays: