drm: Add Virtual DRM device driver

Virtual DRM splits the resources of an overlay plane into multiple
virtual devices to allow each plane to be accessed by each process.

This makes it possible to overlay images output from multiple processes
on a display. For example, one process displays the camera image without
compositor while another process overlays the compositor's drawing of
the UI.

The virtual DRM creates standalone virtual device and make DRM planes
from a master device (e.g. card0) accessible via one or more virtual
devices. However, these plane are no longer accessible from the original
device.
Each virtual device (and plane) can be accessed via a separate
device file.

Signed-off-by: Tomohito Esaki <etom@igel.co.jp>

drivers/gpu/drm/Kconfig

@@ -294,6 +294,13 @@ config DRM_VKMS
 
 	  If M is selected the module will be called vkms.
 
+config DRM_VDRM
+	tristate "Virtual DRM"
+	depends on DRM
+	help
+	  Virtual DRM splits the resources of an overlay plane into multiple
+	  virtual devices to allow each plane to be accessed by each process.
+
 source "drivers/gpu/drm/exynos/Kconfig"
 
 source "drivers/gpu/drm/rockchip/Kconfig"

drivers/gpu/drm/Makefile

@@ -82,6 +82,7 @@ obj-$(CONFIG_DRM_VMWGFX)+= vmwgfx/
 obj-$(CONFIG_DRM_VIA)	+=via/
 obj-$(CONFIG_DRM_VGEM)	+= vgem/
 obj-$(CONFIG_DRM_VKMS)	+= vkms/
+obj-$(CONFIG_DRM_VDRM)	+= vdrm/
 obj-$(CONFIG_DRM_NOUVEAU) +=nouveau/
 obj-$(CONFIG_DRM_EXYNOS) +=exynos/
 obj-$(CONFIG_DRM_ROCKCHIP) +=rockchip/

drivers/gpu/drm/vdrm/vdrm_api.h

@@ -0,0 +1,68 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * vdrm_api.h -- Virtual DRM API
+ *
+ * Copyright (C) 2021 Renesas Electronics Corporation
+ */
+
+#ifndef __VDRM_API__
+#define __VDRM_API__
+
+#include <linux/of_device.h>
+#include <drm/drm_crtc.h>
+
+/**
+ * struct vdrm_property_info - Information about the properties passed from
+ *			       the DRM driver to vDRM
+ * @prop: Parent property to pass to vDRM
+ * @default_val: Default value for the property passed to vDRM
+ */
+struct vdrm_property_info {
+	struct drm_property *prop;
+	uint64_t default_val;
+};
+
+/**
+ * struct vdrm_funcs - Callbacks to parent DRM driver
+ */
+struct vdrm_funcs {
+	/**
+	 * @dumb_create:
+	 *
+	 * Called by &drm_driver.dumb_create. Please read the documentation
+	 * for the &drm_driver.dumb_create hook for more details.
+	 */
+	int (*dumb_create)(struct drm_file *file, struct drm_device *dev,
+			   struct drm_mode_create_dumb *args);
+
+	/**
+	 * @crtc_flush:
+	 *
+	 * Called by &drm_crtc_helper_funcs.atomic_flush. Please read the
+	 * documentation for the &drm_crtc_helper_funcs.atomic_flush hook for
+	 * more details.
+	 */
+	void (*crtc_flush)(struct drm_crtc *crtc);
+};
+
+struct vdrm_device;
+struct vdrm_display;
+
+void vdrm_drv_handle_vblank(struct vdrm_display *vdisplay);
+void vdrm_drv_finish_page_flip(struct vdrm_display *vdisplay);
+struct vdrm_device *vdrm_drv_init(struct drm_device *dev,
+				  struct device_node *np, int num_props,
+				  struct vdrm_property_info *props,
+				  const struct vdrm_funcs *funcs);
+int vdrm_drv_plane_init(struct vdrm_device *vdrm, struct drm_plane *plane,
+			const struct drm_plane_funcs *funcs,
+			const struct drm_plane_helper_funcs *helper_funcs,
+			const u32 *formats, unsigned int num_formats,
+			int max_zpos);
+struct vdrm_display *vdrm_drv_display_init(struct vdrm_device *vdrm,
+					   struct drm_crtc *crtc,
+					   struct drm_plane *plane);
+int vdrm_drv_register(struct vdrm_device *vdrm);
+void vdrm_drv_fini(struct vdrm_device *vdrm);
+
+#endif /* __VDRM_API__ */