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

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 24.02.23 um 19:02 schrieb Rob Clark:
> From: Rob Clark <robdclark@chromium.org>
> 
> 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@chromium.org>
> ---
>   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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