[RFC PATCH 2/2] virtio-gpu: Add an option to connect all outputs on startup

[Damian Hobson-Garcia]

When multiple outputs are enabled using the "max_outputs" attribute,
only the first connector appears as "Connected" in the guest DRM
device.  Additional connectors must be enabled from the host side
UI frontend before they are usable by the guest.  However, multiple
outputs can still be of use on a headless configuration, if for example,
the display will only be used for taking periodic screenshots in the
guest or integration into a CI pipeline, etc.

Add an option to start all of the outputs in the "Connected" state,
so that they are immediately available to the guest.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1107
Signed-off-by: Damian Hobson-Garcia <dhobsong@igel.co.jp>
---
 hw/display/virtio-gpu-base.c   | 12 +++++++++---
 include/hw/virtio/virtio-gpu.h |  7 ++++++-
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/hw/display/virtio-gpu-base.c b/hw/display/virtio-gpu-base.c
index a29f191aa8..885184e302 100644
--- a/hw/display/virtio-gpu-base.c
+++ b/hw/display/virtio-gpu-base.c
@@ -158,6 +158,7 @@ virtio_gpu_base_device_realize(DeviceState *qdev,
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(qdev);
     VirtIOGPUBase *g = VIRTIO_GPU_BASE(qdev);
+    int connected = 1;
     int i;
 
     if (g->conf.max_outputs > VIRTIO_GPU_MAX_SCANOUTS) {
@@ -186,10 +187,15 @@ virtio_gpu_base_device_realize(DeviceState *qdev,
         virtio_add_queue(vdev, 16, cursor_cb);
     }
 
-    g->enabled_output_bitmask = 1;
+    if (virtio_gpu_connect_all_outputs(g->conf))
+        connected = g->conf.max_outputs;
 
-    g->req_state[0].width = g->conf.xres;
-    g->req_state[0].height = g->conf.yres;
+    g->enabled_output_bitmask = (1 << connected) - 1;
+
+    for (i = 0; i < connected; i++) {
+        g->req_state[i].width = g->conf.xres;
+        g->req_state[i].height = g->conf.yres;
+    }
 
     g->hw_ops = &virtio_gpu_ops;
     for (i = 0; i < g->conf.max_outputs; i++) {
diff --git a/include/hw/virtio/virtio-gpu.h b/include/hw/virtio/virtio-gpu.h
index 2e28507efe..54b3eba632 100644
--- a/include/hw/virtio/virtio-gpu.h
+++ b/include/hw/virtio/virtio-gpu.h
@@ -90,6 +90,7 @@ enum virtio_gpu_base_conf_flags {
     VIRTIO_GPU_FLAG_EDID_ENABLED,
     VIRTIO_GPU_FLAG_DMABUF_ENABLED,
     VIRTIO_GPU_FLAG_BLOB_ENABLED,
+    VIRTIO_GPU_FLAG_CONNECT_ALL_OUTPUTS,
 };
 
 #define virtio_gpu_virgl_enabled(_cfg) \
@@ -102,6 +103,8 @@ enum virtio_gpu_base_conf_flags {
     (_cfg.flags & (1 << VIRTIO_GPU_FLAG_DMABUF_ENABLED))
 #define virtio_gpu_blob_enabled(_cfg) \
     (_cfg.flags & (1 << VIRTIO_GPU_FLAG_BLOB_ENABLED))
+#define virtio_gpu_connect_all_outputs(_cfg) \
+    (_cfg.flags & (1 << VIRTIO_GPU_FLAG_CONNECT_ALL_OUTPUTS))
 
 struct virtio_gpu_base_conf {
     uint32_t max_outputs;
@@ -148,7 +151,9 @@ struct VirtIOGPUBaseClass {
     DEFINE_PROP_BIT("edid", _state, _conf.flags, \
                     VIRTIO_GPU_FLAG_EDID_ENABLED, true), \
     DEFINE_PROP_UINT32("xres", _state, _conf.xres, 1280), \
-    DEFINE_PROP_UINT32("yres", _state, _conf.yres, 800)
+    DEFINE_PROP_UINT32("yres", _state, _conf.yres, 800), \
+    DEFINE_PROP_BIT("connect_outputs", _state, _conf.flags, \
+                    VIRTIO_GPU_FLAG_CONNECT_ALL_OUTPUTS, false)
 
 typedef struct VGPUDMABuf {
     QemuDmaBuf buf;
-- 
2.25.1