Re: [PATCH] drm/virtio: Add option to disable KMS support

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Hi

Am 24.02.23 um 19:02 schrieb Rob Clark:
From: Rob Clark <robdclark@xxxxxxxxxxxx>

Add a build option to disable modesetting support.  This is useful in
cases where the guest only needs to use the GPU in a headless mode, or
(such as in the CrOS usage) window surfaces are proxied to a host
compositor.

We've just been discussing this on IRC, but failed to see the practical benefit. It's not like the modesetting code takes up lots of memory. What's the real-world use case?

Best regards
Thomas


Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
---
  drivers/gpu/drm/virtio/Kconfig       | 11 +++++++++++
  drivers/gpu/drm/virtio/Makefile      |  5 ++++-
  drivers/gpu/drm/virtio/virtgpu_drv.c |  6 +++++-
  drivers/gpu/drm/virtio/virtgpu_drv.h | 10 ++++++++++
  drivers/gpu/drm/virtio/virtgpu_kms.c |  6 ++++++
  5 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/virtio/Kconfig b/drivers/gpu/drm/virtio/Kconfig
index 51ec7c3240c9..ea06ff2aa4b4 100644
--- a/drivers/gpu/drm/virtio/Kconfig
+++ b/drivers/gpu/drm/virtio/Kconfig
@@ -11,3 +11,14 @@ config DRM_VIRTIO_GPU
  	   QEMU based VMMs (like KVM or Xen).
If unsure say M.
+
+config DRM_VIRTIO_GPU_KMS
+	bool "Virtio GPU driver modesetting support"
+	depends on DRM_VIRTIO_GPU
+	default y
+	help
+	   Enable modesetting support for virtio GPU driver.  This can be
+	   disabled in cases where only "headless" usage of the GPU is
+	   required.
+
+	   If unsure, say Y.
diff --git a/drivers/gpu/drm/virtio/Makefile b/drivers/gpu/drm/virtio/Makefile
index b99fa4a73b68..24c7ebe87032 100644
--- a/drivers/gpu/drm/virtio/Makefile
+++ b/drivers/gpu/drm/virtio/Makefile
@@ -4,8 +4,11 @@
  # Direct Rendering Infrastructure (DRI) in XFree86 4.1.0 and higher.
virtio-gpu-y := virtgpu_drv.o virtgpu_kms.o virtgpu_gem.o virtgpu_vram.o \
-	virtgpu_display.o virtgpu_vq.o \
+	virtgpu_vq.o \
  	virtgpu_fence.o virtgpu_object.o virtgpu_debugfs.o virtgpu_plane.o \
  	virtgpu_ioctl.o virtgpu_prime.o virtgpu_trace_points.o
+virtio-gpu-$(CONFIG_DRM_VIRTIO_GPU_KMS) += \
+	virtgpu_display.o
+
  obj-$(CONFIG_DRM_VIRTIO_GPU) += virtio-gpu.o
diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c b/drivers/gpu/drm/virtio/virtgpu_drv.c
index ae97b98750b6..9cb7d6dd3da6 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.c
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
@@ -172,7 +172,11 @@ MODULE_AUTHOR("Alon Levy");
  DEFINE_DRM_GEM_FOPS(virtio_gpu_driver_fops);
static const struct drm_driver driver = {
-	.driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_RENDER | DRIVER_ATOMIC,
+	.driver_features =
+#if defined(CONFIG_DRM_VIRTIO_GPU_KMS)
+			DRIVER_MODESET | DRIVER_ATOMIC |
+#endif
+			DRIVER_GEM | DRIVER_RENDER,
  	.open = virtio_gpu_driver_open,
  	.postclose = virtio_gpu_driver_postclose,
diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
index af6ffb696086..ffe8faf67247 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.h
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
@@ -426,8 +426,18 @@ virtio_gpu_cmd_set_scanout_blob(struct virtio_gpu_device *vgdev,
  				uint32_t x, uint32_t y);
/* virtgpu_display.c */
+#if defined(CONFIG_DRM_VIRTIO_GPU_KMS)
  int virtio_gpu_modeset_init(struct virtio_gpu_device *vgdev);
  void virtio_gpu_modeset_fini(struct virtio_gpu_device *vgdev);
+#else
+static inline int virtio_gpu_modeset_init(struct virtio_gpu_device *vgdev)
+{
+	return 0;
+}
+static inline void virtio_gpu_modeset_fini(struct virtio_gpu_device *vgdev)
+{
+}
+#endif
/* virtgpu_plane.c */
  uint32_t virtio_gpu_translate_format(uint32_t drm_fourcc);
diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c
index 27b7f14dae89..293e6f0bf133 100644
--- a/drivers/gpu/drm/virtio/virtgpu_kms.c
+++ b/drivers/gpu/drm/virtio/virtgpu_kms.c
@@ -161,9 +161,11 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev)
  	if (virtio_has_feature(vgdev->vdev, VIRTIO_GPU_F_VIRGL))
  		vgdev->has_virgl_3d = true;
  #endif
+#if defined(CONFIG_DRM_VIRTIO_GPU_KMS)
  	if (virtio_has_feature(vgdev->vdev, VIRTIO_GPU_F_EDID)) {
  		vgdev->has_edid = true;
  	}
+#endif
  	if (virtio_has_feature(vgdev->vdev, VIRTIO_RING_F_INDIRECT_DESC)) {
  		vgdev->has_indirect = true;
  	}
@@ -218,6 +220,7 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev)
  		goto err_vbufs;
  	}
+#if defined(CONFIG_DRM_VIRTIO_GPU_KMS)
  	/* get display info */
  	virtio_cread_le(vgdev->vdev, struct virtio_gpu_config,
  			num_scanouts, &num_scanouts);
@@ -229,6 +232,7 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev)
  		goto err_scanouts;
  	}
  	DRM_INFO("number of scanouts: %d\n", num_scanouts);
+#endif
virtio_cread_le(vgdev->vdev, struct virtio_gpu_config,
  			num_capsets, &num_capsets);
@@ -246,10 +250,12 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev)
  		virtio_gpu_get_capsets(vgdev, num_capsets);
  	if (vgdev->has_edid)
  		virtio_gpu_cmd_get_edids(vgdev);
+#if defined(CONFIG_DRM_VIRTIO_GPU_KMS)
  	virtio_gpu_cmd_get_display_info(vgdev);
  	virtio_gpu_notify(vgdev);
  	wait_event_timeout(vgdev->resp_wq, !vgdev->display_info_pending,
  			   5 * HZ);
+#endif
  	return 0;
err_scanouts:

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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