[PATCH v2 2/3] virtio-gpu: decouple Venus from CONFIG_OPENGL

[Lucas Amaral <lucaaamaral@gmail.com>]

Venus (virtio-gpu Vulkan context) currently requires an OpenGL
display backend due to build-time and runtime coupling.  On macOS,
no OpenGL display backend exists.

Remove the opengl.found() build requirement for the virtio-gpu-gl
module; virglrenderer provides Venus independently of OpenGL.

Gate GL-specific code paths behind CONFIG_OPENGL and display_opengl:
- Only advertise VIRGL/VIRGL2 capsets when display_opengl is set
- Only pass VIRGL_RENDERER_NO_VIRGL when !display_opengl with Venus
- Null out GL context callbacks when no GL display is available
- Route 2D display commands to the software renderer (pixman) when
  Venus runs without GL (venus no-GL mode)
- Allow Venus to bypass the OpenGL display check at device realize

Signed-off-by: Lucas Amaral <lucaaamaral@gmail.com>
---
 hw/display/meson.build        |  8 ++--
 hw/display/virtio-gpu-base.c  | 15 ++++++-
 hw/display/virtio-gpu-gl.c    |  6 ++-
 hw/display/virtio-gpu-virgl.c | 84 ++++++++++++++++++++++++++++++-----
 4 files changed, 97 insertions(+), 16 deletions(-)

diff --git a/hw/display/meson.build b/hw/display/meson.build
index 90e6c04..509479e 100644
--- a/hw/display/meson.build
+++ b/hw/display/meson.build
@@ -76,9 +76,9 @@ if config_all_devices.has_key('CONFIG_VIRTIO_GPU')
   virtio_gpu_ss.add(when: 'CONFIG_VHOST_USER_GPU', if_true: files('vhost-user-gpu.c'))
   hw_display_modules += {'virtio-gpu': virtio_gpu_ss}
 
-  if virgl.found() and opengl.found()
+  if virgl.found()
     virtio_gpu_gl_ss = ss.source_set()
-    virtio_gpu_gl_ss.add(when: ['CONFIG_VIRTIO_GPU', virgl, opengl],
+    virtio_gpu_gl_ss.add(when: ['CONFIG_VIRTIO_GPU', virgl],
                          if_true: [files('virtio-gpu-gl.c', 'virtio-gpu-virgl.c'), pixman, virgl])
     hw_display_modules += {'virtio-gpu-gl': virtio_gpu_gl_ss}
   endif
@@ -99,9 +99,9 @@ if config_all_devices.has_key('CONFIG_VIRTIO_PCI')
                         if_true: files('vhost-user-gpu-pci.c'))
   hw_display_modules += {'virtio-gpu-pci': virtio_gpu_pci_ss}
 
-  if virgl.found() and opengl.found()
+  if virgl.found()
     virtio_gpu_pci_gl_ss = ss.source_set()
-    virtio_gpu_pci_gl_ss.add(when: ['CONFIG_VIRTIO_GPU', 'CONFIG_VIRTIO_PCI', virgl, opengl],
+    virtio_gpu_pci_gl_ss.add(when: ['CONFIG_VIRTIO_GPU', 'CONFIG_VIRTIO_PCI', virgl],
                              if_true: [files('virtio-gpu-pci-gl.c'), pixman])
     hw_display_modules += {'virtio-gpu-pci-gl': virtio_gpu_pci_gl_ss}
   endif
diff --git a/hw/display/virtio-gpu-base.c b/hw/display/virtio-gpu-base.c
index 7269477..dd93b65 100644
--- a/hw/display/virtio-gpu-base.c
+++ b/hw/display/virtio-gpu-base.c
@@ -18,6 +18,7 @@
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "hw/display/edid.h"
+#include "system/system.h"
 #include "trace.h"
 #include "qapi/qapi-types-virtio.h"
 
@@ -157,7 +158,18 @@ virtio_gpu_get_flags(void *opaque)
     VirtIOGPUBase *g = opaque;
     int flags = GRAPHIC_FLAGS_NONE;
 
-    if (virtio_gpu_virgl_enabled(g->conf)) {
+    if (virtio_gpu_venus_enabled(g->conf)) {
+        /* TODO: set GRAPHIC_FLAGS_VK for direct Vulkan scanout */
+    }
+
+    /*
+     * TODO: virtio_gpu_virgl_enabled() checks VIRTIO_GPU_FLAG_VIRGL_ENABLED
+     * which is set for both OpenGL (VIRGL) and Vulkan (Venus) backends.
+     * This condition should ideally use a dedicated OpenGL-only flag. For
+     * now, display_opengl correctly gates GL scanout since Venus leaves it
+     * at 0.
+     */
+    if (virtio_gpu_virgl_enabled(g->conf) && display_opengl) {
         flags |= GRAPHIC_FLAGS_GL;
     }
 
@@ -257,6 +269,7 @@ virtio_gpu_base_get_features(VirtIODevice *vdev, uint64_t features,
     }
     if (virtio_gpu_blob_enabled(g->conf)) {
         features |= (1 << VIRTIO_GPU_F_RESOURCE_BLOB);
+        features |= (1 << VIRTIO_GPU_F_BLOB_ALIGNMENT);
     }
     if (virtio_gpu_context_init_enabled(g->conf)) {
         features |= (1 << VIRTIO_GPU_F_CONTEXT_INIT);
diff --git a/hw/display/virtio-gpu-gl.c b/hw/display/virtio-gpu-gl.c
index b98ef2e..b5526cd 100644
--- a/hw/display/virtio-gpu-gl.c
+++ b/hw/display/virtio-gpu-gl.c
@@ -133,7 +133,9 @@ static void virtio_gpu_gl_device_realize(DeviceState *qdev, Error **errp)
         return;
     }
 
-    if (!display_opengl) {
+    if (virtio_gpu_venus_enabled(g->parent_obj.conf)) {
+        /* Venus renders via Vulkan in the render server — no GL display needed */
+    } else if (!display_opengl) {
         error_setg(errp,
                    "The display backend does not have OpenGL support enabled");
         error_append_hint(errp,
@@ -217,4 +219,6 @@ static void virtio_register_types(void)
 type_init(virtio_register_types)
 
 module_dep("hw-display-virtio-gpu");
+#ifdef CONFIG_OPENGL
 module_dep("ui-opengl");
+#endif
diff --git a/hw/display/virtio-gpu-virgl.c b/hw/display/virtio-gpu-virgl.c
index 0f75482..66a70e3 100644
--- a/hw/display/virtio-gpu-virgl.c
+++ b/hw/display/virtio-gpu-virgl.c
@@ -19,8 +19,10 @@
 #include "hw/virtio/virtio-gpu.h"
 #include "hw/virtio/virtio-gpu-bswap.h"
 #include "hw/virtio/virtio-gpu-pixman.h"
-
+#include "system/system.h"
+#ifdef CONFIG_OPENGL
 #include "ui/egl-helpers.h"
+#endif
 
 #include <virglrenderer.h>
 
@@ -29,6 +31,16 @@ struct virtio_gpu_virgl_resource {
     MemoryRegion *mr;
 };
 
+/*
+ * Venus no-GL mode: Venus is enabled but no OpenGL display is available.
+ * Display commands use software (pixman) rendering; Venus/3D commands
+ * go through the virglrenderer render server.
+ */
+static bool virtio_gpu_venus_nogl(VirtIOGPU *g)
+{
+    return virtio_gpu_venus_enabled(g->parent_obj.conf) && !display_opengl;
+}
+
 static struct virtio_gpu_virgl_resource *
 virtio_gpu_virgl_find_resource(VirtIOGPU *g, uint32_t resource_id)
 {
@@ -42,7 +54,7 @@ virtio_gpu_virgl_find_resource(VirtIOGPU *g, uint32_t resource_id)
     return container_of(res, struct virtio_gpu_virgl_resource, base);
 }
 
-#if VIRGL_RENDERER_CALLBACKS_VERSION >= 4
+#if VIRGL_RENDERER_CALLBACKS_VERSION >= 4 && defined(CONFIG_OPENGL)
 static void *
 virgl_get_egl_display(G_GNUC_UNUSED void *cookie)
 {
@@ -903,6 +915,44 @@ void virtio_gpu_virgl_process_cmd(VirtIOGPU *g,
 
     VIRTIO_GPU_FILL_CMD(cmd->cmd_hdr);
 
+    /*
+     * Venus no-GL mode: route 2D display commands to the base software
+     * renderer (pixman). The guest kernel always uses 2D commands for
+     * display framebuffers even with VIRGL enabled; Venus/3D commands
+     * go through the virglrenderer render server as usual.
+     */
+    if (virtio_gpu_venus_nogl(g)) {
+        switch (cmd->cmd_hdr.type) {
+        case VIRTIO_GPU_CMD_RESOURCE_CREATE_2D:
+        case VIRTIO_GPU_CMD_SET_SCANOUT:
+        case VIRTIO_GPU_CMD_RESOURCE_FLUSH:
+        case VIRTIO_GPU_CMD_TRANSFER_TO_HOST_2D:
+        case VIRTIO_GPU_CMD_GET_DISPLAY_INFO:
+        case VIRTIO_GPU_CMD_GET_EDID:
+            virtio_gpu_simple_process_cmd(g, cmd);
+            return;
+        case VIRTIO_GPU_CMD_RESOURCE_UNREF:
+        case VIRTIO_GPU_CMD_RESOURCE_ATTACH_BACKING:
+        case VIRTIO_GPU_CMD_RESOURCE_DETACH_BACKING: {
+            /*
+             * Both 2D (simple) and blob (virgl) resources share g->reslist.
+             * Check if virglrenderer owns the resource to pick the right handler.
+             */
+            struct virtio_gpu_resource_unref hdr;
+            struct virgl_renderer_resource_info info;
+            VIRTIO_GPU_FILL_CMD(hdr);
+            if (virgl_renderer_resource_get_info(hdr.resource_id, &info)) {
+                /* Not in virglrenderer — it's a 2D software resource */
+                virtio_gpu_simple_process_cmd(g, cmd);
+                return;
+            }
+            break; /* virglrenderer owns it — fall through */
+        }
+        default:
+            break;
+        }
+    }
+
     virgl_renderer_force_ctx_0();
     switch (cmd->cmd_hdr.type) {
     case VIRTIO_GPU_CMD_CTX_CREATE:
@@ -1169,6 +1219,7 @@ int virtio_gpu_virgl_init(VirtIOGPU *g)
     uint32_t flags = 0;
     VirtIOGPUGL *gl = VIRTIO_GPU_GL(g);
 
+#ifdef CONFIG_OPENGL
 #if VIRGL_RENDERER_CALLBACKS_VERSION >= 4
     if (qemu_egl_display) {
         virtio_gpu_3d_cbs.version = 4;
@@ -1180,12 +1231,23 @@ int virtio_gpu_virgl_init(VirtIOGPU *g)
         flags |= VIRGL_RENDERER_D3D11_SHARE_TEXTURE;
     }
 #endif
+#endif /* CONFIG_OPENGL */
 #if VIRGL_VERSION_MAJOR >= 1
     if (virtio_gpu_venus_enabled(g->parent_obj.conf)) {
-        flags |= VIRGL_RENDERER_VENUS | VIRGL_RENDERER_RENDER_SERVER;
+        flags |= VIRGL_RENDERER_VENUS
+               | VIRGL_RENDERER_RENDER_SERVER;
+        if (!display_opengl) {
+            flags |= VIRGL_RENDERER_NO_VIRGL;
+        }
     }
 #endif
 
+    if (!display_opengl) {
+        virtio_gpu_3d_cbs.create_gl_context = NULL;
+        virtio_gpu_3d_cbs.destroy_gl_context = NULL;
+        virtio_gpu_3d_cbs.make_current = NULL;
+    }
+
     ret = virgl_renderer_init(g, flags, &virtio_gpu_3d_cbs);
     if (ret != 0) {
         error_report("virgl could not be initialized: %d", ret);
@@ -1223,14 +1285,16 @@ GArray *virtio_gpu_virgl_get_capsets(VirtIOGPU *g)
 
     capset_ids = g_array_new(false, false, sizeof(uint32_t));
 
-    /* VIRGL is always supported. */
-    virtio_gpu_virgl_add_capset(capset_ids, VIRTIO_GPU_CAPSET_VIRGL);
+    /* OpenGL: VIRGL/VIRGL2 require a GL display backend */
+    if (display_opengl) {
+        virtio_gpu_virgl_add_capset(capset_ids, VIRTIO_GPU_CAPSET_VIRGL);
 
-    virgl_renderer_get_cap_set(VIRTIO_GPU_CAPSET_VIRGL2,
-                               &capset_max_ver,
-                               &capset_max_size);
-    if (capset_max_ver) {
-        virtio_gpu_virgl_add_capset(capset_ids, VIRTIO_GPU_CAPSET_VIRGL2);
+        virgl_renderer_get_cap_set(VIRTIO_GPU_CAPSET_VIRGL2,
+                                   &capset_max_ver,
+                                   &capset_max_size);
+        if (capset_max_ver) {
+            virtio_gpu_virgl_add_capset(capset_ids, VIRTIO_GPU_CAPSET_VIRGL2);
+        }
     }
 
     if (virtio_gpu_venus_enabled(g->parent_obj.conf)) {
-- 
2.52.0