kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

6 files changed, 1289 insertions, 0 deletions

diff --git a/drivers/gpu/drm/hyperv/Kconfig b/drivers/gpu/drm/hyperv/Kconfig
new file mode 100644
index 000000000..86234f6a7
--- /dev/null
+++ b/drivers/gpu/drm/hyperv/Kconfig
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config DRM_HYPERV
+	tristate "DRM Support for Hyper-V synthetic video device"
+	depends on DRM && PCI && HYPERV_VMBUS
+	select DRM_CLIENT_SELECTION
+	select DRM_KMS_HELPER
+	select DRM_GEM_SHMEM_HELPER
+	help
+	 This is a KMS driver for Hyper-V synthetic video device. Choose this
+	 option if you would like to enable drm driver for Hyper-V virtual
+	 machine. Unselect Hyper-V framebuffer driver (CONFIG_FB_HYPERV) so
+	 that DRM driver is used by default.
+
+	 If M is selected the module will be called hyperv_drm.
diff --git a/drivers/gpu/drm/hyperv/Makefile b/drivers/gpu/drm/hyperv/Makefile
new file mode 100644
index 000000000..265f12f2c
--- /dev/null
+++ b/drivers/gpu/drm/hyperv/Makefile
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+hyperv_drm-y := \
+	hyperv_drm_drv.o \
+	hyperv_drm_modeset.o \
+	hyperv_drm_proto.o
+
+obj-$(CONFIG_DRM_HYPERV) += hyperv_drm.o
diff --git a/drivers/gpu/drm/hyperv/hyperv_drm.h b/drivers/gpu/drm/hyperv/hyperv_drm.h
new file mode 100644
index 000000000..9e776112c
--- /dev/null
+++ b/drivers/gpu/drm/hyperv/hyperv_drm.h
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2021 Microsoft
+ */
+
+#ifndef _HYPERV_DRM_H_
+#define _HYPERV_DRM_H_
+
+#define VMBUS_MAX_PACKET_SIZE 0x4000
+
+struct hyperv_drm_device {
+	/* drm */
+	struct drm_device dev;
+	struct drm_plane plane;
+	struct drm_crtc crtc;
+	struct drm_encoder encoder;
+	struct drm_connector connector;
+
+	/* mode */
+	u32 screen_width_max;
+	u32 screen_height_max;
+	u32 preferred_width;
+	u32 preferred_height;
+	u32 screen_depth;
+
+	/* hw */
+	struct resource *mem;
+	void __iomem *vram;
+	unsigned long fb_base;
+	unsigned long fb_size;
+	struct completion wait;
+	u32 synthvid_version;
+	u32 mmio_megabytes;
+	bool dirt_needed;
+
+	u8 init_buf[VMBUS_MAX_PACKET_SIZE];
+	u8 recv_buf[VMBUS_MAX_PACKET_SIZE];
+
+	struct hv_device *hdev;
+};
+
+#define to_hv(_dev) container_of(_dev, struct hyperv_drm_device, dev)
+
+/* hyperv_drm_modeset */
+int hyperv_mode_config_init(struct hyperv_drm_device *hv);
+
+/* hyperv_drm_proto */
+int hyperv_update_vram_location(struct hv_device *hdev, phys_addr_t vram_pp);
+int hyperv_update_situation(struct hv_device *hdev, u8 active, u32 bpp,
+			    u32 w, u32 h, u32 pitch);
+int hyperv_hide_hw_ptr(struct hv_device *hdev);
+int hyperv_update_dirt(struct hv_device *hdev, struct drm_rect *rect);
+int hyperv_connect_vsp(struct hv_device *hdev);
+
+#endif
diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_drv.c b/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
new file mode 100644
index 000000000..b6bf6412a
--- /dev/null
+++ b/drivers/gpu/drm/hyperv/hyperv_drm_drv.c
@@ -0,0 +1,268 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2021 Microsoft
+ */
+
+#include <linux/aperture.h>
+#include <linux/efi.h>
+#include <linux/hyperv.h>
+#include <linux/module.h>
+#include <linux/pci.h>
+
+#include <drm/clients/drm_client_setup.h>
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_fbdev_shmem.h>
+#include <drm/drm_gem_shmem_helper.h>
+#include <drm/drm_print.h>
+#include <drm/drm_simple_kms_helper.h>
+
+#include "hyperv_drm.h"
+
+#define DRIVER_NAME "hyperv_drm"
+#define DRIVER_DESC "DRM driver for Hyper-V synthetic video device"
+#define DRIVER_MAJOR 1
+#define DRIVER_MINOR 0
+
+DEFINE_DRM_GEM_FOPS(hv_fops);
+
+static struct drm_driver hyperv_driver = {
+	.driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_ATOMIC,
+
+	.name		 = DRIVER_NAME,
+	.desc		 = DRIVER_DESC,
+	.major		 = DRIVER_MAJOR,
+	.minor		 = DRIVER_MINOR,
+
+	.fops		 = &hv_fops,
+	DRM_GEM_SHMEM_DRIVER_OPS,
+	DRM_FBDEV_SHMEM_DRIVER_OPS,
+};
+
+static int hyperv_pci_probe(struct pci_dev *pdev,
+			    const struct pci_device_id *ent)
+{
+	return 0;
+}
+
+static void hyperv_pci_remove(struct pci_dev *pdev)
+{
+}
+
+static const struct pci_device_id hyperv_pci_tbl[] = {
+	{
+		.vendor = PCI_VENDOR_ID_MICROSOFT,
+		.device = PCI_DEVICE_ID_HYPERV_VIDEO,
+	},
+	{ /* end of list */ }
+};
+
+/*
+ * PCI stub to support gen1 VM.
+ */
+static struct pci_driver hyperv_pci_driver = {
+	.name =		KBUILD_MODNAME,
+	.id_table =	hyperv_pci_tbl,
+	.probe =	hyperv_pci_probe,
+	.remove =	hyperv_pci_remove,
+};
+
+static int hyperv_setup_vram(struct hyperv_drm_device *hv,
+			     struct hv_device *hdev)
+{
+	struct drm_device *dev = &hv->dev;
+	int ret;
+
+	hv->fb_size = (unsigned long)hv->mmio_megabytes * 1024 * 1024;
+
+	ret = vmbus_allocate_mmio(&hv->mem, hdev, 0, -1, hv->fb_size, 0x100000,
+				  true);
+	if (ret) {
+		drm_err(dev, "Failed to allocate mmio\n");
+		return -ENOMEM;
+	}
+
+	/*
+	 * Map the VRAM cacheable for performance. This is also required for VM
+	 * connect to display properly for ARM64 Linux VM, as the host also maps
+	 * the VRAM cacheable.
+	 */
+	hv->vram = ioremap_cache(hv->mem->start, hv->fb_size);
+	if (!hv->vram) {
+		drm_err(dev, "Failed to map vram\n");
+		ret = -ENOMEM;
+		goto error;
+	}
+
+	hv->fb_base = hv->mem->start;
+	return 0;
+
+error:
+	vmbus_free_mmio(hv->mem->start, hv->fb_size);
+	return ret;
+}
+
+static int hyperv_vmbus_probe(struct hv_device *hdev,
+			      const struct hv_vmbus_device_id *dev_id)
+{
+	struct hyperv_drm_device *hv;
+	struct drm_device *dev;
+	int ret;
+
+	hv = devm_drm_dev_alloc(&hdev->device, &hyperv_driver,
+				struct hyperv_drm_device, dev);
+	if (IS_ERR(hv))
+		return PTR_ERR(hv);
+
+	dev = &hv->dev;
+	init_completion(&hv->wait);
+	hv_set_drvdata(hdev, hv);
+	hv->hdev = hdev;
+
+	ret = hyperv_connect_vsp(hdev);
+	if (ret) {
+		drm_err(dev, "Failed to connect to vmbus.\n");
+		goto err_hv_set_drv_data;
+	}
+
+	aperture_remove_all_conflicting_devices(hyperv_driver.name);
+
+	ret = hyperv_setup_vram(hv, hdev);
+	if (ret)
+		goto err_vmbus_close;
+
+	/*
+	 * Should be done only once during init and resume. Failing to update
+	 * vram location is not fatal. Device will update dirty area till
+	 * preferred resolution only.
+	 */
+	ret = hyperv_update_vram_location(hdev, hv->fb_base);
+	if (ret)
+		drm_warn(dev, "Failed to update vram location.\n");
+
+	ret = hyperv_mode_config_init(hv);
+	if (ret)
+		goto err_free_mmio;
+
+	ret = drm_dev_register(dev, 0);
+	if (ret) {
+		drm_err(dev, "Failed to register drm driver.\n");
+		goto err_free_mmio;
+	}
+
+	/* If DRM panic path is stubbed out VMBus code must do the unload */
+	if (IS_ENABLED(CONFIG_DRM_PANIC))
+		vmbus_set_skip_unload(true);
+
+	drm_client_setup(dev, NULL);
+
+	return 0;
+
+err_free_mmio:
+	iounmap(hv->vram);
+	vmbus_free_mmio(hv->mem->start, hv->fb_size);
+err_vmbus_close:
+	vmbus_close(hdev->channel);
+err_hv_set_drv_data:
+	hv_set_drvdata(hdev, NULL);
+	return ret;
+}
+
+static void hyperv_vmbus_remove(struct hv_device *hdev)
+{
+	struct drm_device *dev = hv_get_drvdata(hdev);
+	struct hyperv_drm_device *hv = to_hv(dev);
+
+	vmbus_set_skip_unload(false);
+	drm_dev_unplug(dev);
+	drm_atomic_helper_shutdown(dev);
+	vmbus_close(hdev->channel);
+	hv_set_drvdata(hdev, NULL);
+
+	iounmap(hv->vram);
+	vmbus_free_mmio(hv->mem->start, hv->fb_size);
+}
+
+static void hyperv_vmbus_shutdown(struct hv_device *hdev)
+{
+	drm_atomic_helper_shutdown(hv_get_drvdata(hdev));
+}
+
+static int hyperv_vmbus_suspend(struct hv_device *hdev)
+{
+	struct drm_device *dev = hv_get_drvdata(hdev);
+	int ret;
+
+	ret = drm_mode_config_helper_suspend(dev);
+	if (ret)
+		return ret;
+
+	vmbus_close(hdev->channel);
+
+	return 0;
+}
+
+static int hyperv_vmbus_resume(struct hv_device *hdev)
+{
+	struct drm_device *dev = hv_get_drvdata(hdev);
+	struct hyperv_drm_device *hv = to_hv(dev);
+	int ret;
+
+	ret = hyperv_connect_vsp(hdev);
+	if (ret)
+		return ret;
+
+	ret = hyperv_update_vram_location(hdev, hv->fb_base);
+	if (ret)
+		return ret;
+
+	return drm_mode_config_helper_resume(dev);
+}
+
+static const struct hv_vmbus_device_id hyperv_vmbus_tbl[] = {
+	/* Synthetic Video Device GUID */
+	{HV_SYNTHVID_GUID},
+	{}
+};
+
+static struct hv_driver hyperv_hv_driver = {
+	.name = KBUILD_MODNAME,
+	.id_table = hyperv_vmbus_tbl,
+	.probe = hyperv_vmbus_probe,
+	.remove = hyperv_vmbus_remove,
+	.shutdown = hyperv_vmbus_shutdown,
+	.suspend = hyperv_vmbus_suspend,
+	.resume = hyperv_vmbus_resume,
+	.driver = {
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+
+static int __init hyperv_init(void)
+{
+	int ret;
+
+	if (drm_firmware_drivers_only())
+		return -ENODEV;
+
+	ret = pci_register_driver(&hyperv_pci_driver);
+	if (ret != 0)
+		return ret;
+
+	return vmbus_driver_register(&hyperv_hv_driver);
+}
+
+static void __exit hyperv_exit(void)
+{
+	vmbus_driver_unregister(&hyperv_hv_driver);
+	pci_unregister_driver(&hyperv_pci_driver);
+}
+
+module_init(hyperv_init);
+module_exit(hyperv_exit);
+
+MODULE_DEVICE_TABLE(pci, hyperv_pci_tbl);
+MODULE_DEVICE_TABLE(vmbus, hyperv_vmbus_tbl);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Deepak Rawat <drawat.floss@gmail.com>");
+MODULE_DESCRIPTION("DRM driver for Hyper-V synthetic video device");
diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c b/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c
new file mode 100644
index 000000000..793dbbf61
--- /dev/null
+++ b/drivers/gpu/drm/hyperv/hyperv_drm_modeset.c
@@ -0,0 +1,340 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2021 Microsoft
+ */
+
+#include <linux/hyperv.h>
+
+#include <drm/drm_atomic.h>
+#include <drm/drm_crtc_helper.h>
+#include <drm/drm_damage_helper.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_edid.h>
+#include <drm/drm_format_helper.h>
+#include <drm/drm_fourcc.h>
+#include <drm/drm_framebuffer.h>
+#include <drm/drm_gem_atomic_helper.h>
+#include <drm/drm_gem_framebuffer_helper.h>
+#include <drm/drm_gem_shmem_helper.h>
+#include <drm/drm_probe_helper.h>
+#include <drm/drm_panic.h>
+#include <drm/drm_plane.h>
+#include <drm/drm_print.h>
+#include <drm/drm_vblank.h>
+#include <drm/drm_vblank_helper.h>
+
+#include "hyperv_drm.h"
+
+static int hyperv_blit_to_vram_rect(struct drm_framebuffer *fb,
+				    const struct iosys_map *vmap,
+				    struct drm_rect *rect)
+{
+	struct hyperv_drm_device *hv = to_hv(fb->dev);
+	struct iosys_map dst = IOSYS_MAP_INIT_VADDR_IOMEM(hv->vram);
+	int idx;
+
+	if (!drm_dev_enter(&hv->dev, &idx))
+		return -ENODEV;
+
+	iosys_map_incr(&dst, drm_fb_clip_offset(fb->pitches[0], fb->format, rect));
+	drm_fb_memcpy(&dst, fb->pitches, vmap, fb, rect);
+
+	drm_dev_exit(idx);
+
+	return 0;
+}
+
+static int hyperv_connector_get_modes(struct drm_connector *connector)
+{
+	struct hyperv_drm_device *hv = to_hv(connector->dev);
+	int count;
+
+	count = drm_add_modes_noedid(connector,
+				     connector->dev->mode_config.max_width,
+				     connector->dev->mode_config.max_height);
+	drm_set_preferred_mode(connector, hv->preferred_width,
+			       hv->preferred_height);
+
+	return count;
+}
+
+static const struct drm_connector_helper_funcs hyperv_connector_helper_funcs = {
+	.get_modes = hyperv_connector_get_modes,
+};
+
+static const struct drm_connector_funcs hyperv_connector_funcs = {
+	.fill_modes = drm_helper_probe_single_connector_modes,
+	.destroy = drm_connector_cleanup,
+	.reset = drm_atomic_helper_connector_reset,
+	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
+};
+
+static inline int hyperv_conn_init(struct hyperv_drm_device *hv)
+{
+	drm_connector_helper_add(&hv->connector, &hyperv_connector_helper_funcs);
+	return drm_connector_init(&hv->dev, &hv->connector,
+				  &hyperv_connector_funcs,
+				  DRM_MODE_CONNECTOR_VIRTUAL);
+}
+
+static int hyperv_check_size(struct hyperv_drm_device *hv, int w, int h,
+			     struct drm_framebuffer *fb)
+{
+	u32 pitch = w * (hv->screen_depth / 8);
+
+	if (fb)
+		pitch = fb->pitches[0];
+
+	if (pitch * h > hv->fb_size)
+		return -EINVAL;
+
+	return 0;
+}
+
+static const uint32_t hyperv_formats[] = {
+	DRM_FORMAT_XRGB8888,
+};
+
+static const uint64_t hyperv_modifiers[] = {
+	DRM_FORMAT_MOD_LINEAR,
+	DRM_FORMAT_MOD_INVALID
+};
+
+static void hyperv_crtc_helper_atomic_enable(struct drm_crtc *crtc,
+					     struct drm_atomic_commit *state)
+{
+	struct hyperv_drm_device *hv = to_hv(crtc->dev);
+	struct drm_plane *plane = &hv->plane;
+	struct drm_plane_state *plane_state = plane->state;
+	struct drm_crtc_state *crtc_state = crtc->state;
+
+	hyperv_hide_hw_ptr(hv->hdev);
+	hyperv_update_situation(hv->hdev, 1,  hv->screen_depth,
+				crtc_state->mode.hdisplay,
+				crtc_state->mode.vdisplay,
+				plane_state->fb->pitches[0]);
+
+	drm_crtc_vblank_on(crtc);
+}
+
+static const struct drm_crtc_helper_funcs hyperv_crtc_helper_funcs = {
+	.atomic_check = drm_crtc_helper_atomic_check,
+	.atomic_flush = drm_crtc_vblank_atomic_flush,
+	.atomic_enable = hyperv_crtc_helper_atomic_enable,
+	.atomic_disable = drm_crtc_vblank_atomic_disable,
+};
+
+static const struct drm_crtc_funcs hyperv_crtc_funcs = {
+	.reset = drm_atomic_helper_crtc_reset,
+	.destroy = drm_crtc_cleanup,
+	.set_config = drm_atomic_helper_set_config,
+	.page_flip = drm_atomic_helper_page_flip,
+	.atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
+	DRM_CRTC_VBLANK_TIMER_FUNCS,
+};
+
+static int hyperv_plane_atomic_check(struct drm_plane *plane,
+				     struct drm_atomic_commit *state)
+{
+	struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
+	struct hyperv_drm_device *hv = to_hv(plane->dev);
+	struct drm_framebuffer *fb = plane_state->fb;
+	struct drm_crtc *crtc = plane_state->crtc;
+	struct drm_crtc_state *crtc_state = NULL;
+	int ret;
+
+	if (crtc)
+		crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
+
+	ret = drm_atomic_helper_check_plane_state(plane_state, crtc_state,
+						  DRM_PLANE_NO_SCALING,
+						  DRM_PLANE_NO_SCALING,
+						  false, false);
+	if (ret)
+		return ret;
+
+	if (!plane_state->visible)
+		return 0;
+
+	if (fb->pitches[0] * fb->height > hv->fb_size) {
+		drm_err(&hv->dev, "fb size requested by %s for %dX%d (pitch %d) greater than %ld\n",
+			current->comm, fb->width, fb->height, fb->pitches[0], hv->fb_size);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static void hyperv_plane_atomic_update(struct drm_plane *plane,
+				       struct drm_atomic_commit *state)
+{
+	struct hyperv_drm_device *hv = to_hv(plane->dev);
+	struct drm_plane_state *old_state = drm_atomic_get_old_plane_state(state, plane);
+	struct drm_plane_state *new_state = drm_atomic_get_new_plane_state(state, plane);
+	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(new_state);
+	struct drm_rect damage;
+	struct drm_rect dst_clip;
+	struct drm_atomic_helper_damage_iter iter;
+
+	drm_atomic_helper_damage_iter_init(&iter, old_state, new_state);
+	drm_atomic_for_each_plane_damage(&iter, &damage) {
+		dst_clip = new_state->dst;
+
+		if (!drm_rect_intersect(&dst_clip, &damage))
+			continue;
+
+		hyperv_blit_to_vram_rect(new_state->fb, &shadow_plane_state->data[0], &damage);
+		hyperv_update_dirt(hv->hdev, &damage);
+	}
+}
+
+static int hyperv_plane_get_scanout_buffer(struct drm_plane *plane,
+					   struct drm_scanout_buffer *sb)
+{
+	struct hyperv_drm_device *hv = to_hv(plane->dev);
+	struct iosys_map map = IOSYS_MAP_INIT_VADDR_IOMEM(hv->vram);
+
+	if (plane->state && plane->state->fb) {
+		sb->format = plane->state->fb->format;
+		sb->width = plane->state->fb->width;
+		sb->height = plane->state->fb->height;
+		sb->pitch[0] = plane->state->fb->pitches[0];
+		sb->map[0] = map;
+		return 0;
+	}
+	return -ENODEV;
+}
+
+static void hyperv_plane_panic_flush(struct drm_plane *plane)
+{
+	struct hyperv_drm_device *hv = to_hv(plane->dev);
+	struct drm_rect rect;
+
+	if (plane->state && plane->state->fb) {
+		rect.x1 = 0;
+		rect.y1 = 0;
+		rect.x2 = plane->state->fb->width;
+		rect.y2 = plane->state->fb->height;
+
+		hyperv_update_dirt(hv->hdev, &rect);
+	}
+
+	vmbus_initiate_unload(true);
+}
+
+static const struct drm_plane_helper_funcs hyperv_plane_helper_funcs = {
+	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
+	.atomic_check = hyperv_plane_atomic_check,
+	.atomic_update = hyperv_plane_atomic_update,
+	.get_scanout_buffer = hyperv_plane_get_scanout_buffer,
+	.panic_flush = hyperv_plane_panic_flush,
+};
+
+static const struct drm_plane_funcs hyperv_plane_funcs = {
+	.update_plane		= drm_atomic_helper_update_plane,
+	.disable_plane		= drm_atomic_helper_disable_plane,
+	.destroy		= drm_plane_cleanup,
+	DRM_GEM_SHADOW_PLANE_FUNCS,
+};
+
+static const struct drm_encoder_funcs hyperv_drm_simple_encoder_funcs_cleanup = {
+	.destroy = drm_encoder_cleanup,
+};
+
+static inline int hyperv_pipe_init(struct hyperv_drm_device *hv)
+{
+	struct drm_device *dev = &hv->dev;
+	struct drm_encoder *encoder = &hv->encoder;
+	struct drm_plane *plane = &hv->plane;
+	struct drm_crtc *crtc = &hv->crtc;
+	struct drm_connector *connector = &hv->connector;
+	int ret;
+
+	ret = drm_universal_plane_init(dev, plane, 0,
+				       &hyperv_plane_funcs,
+				       hyperv_formats, ARRAY_SIZE(hyperv_formats),
+				       hyperv_modifiers,
+				       DRM_PLANE_TYPE_PRIMARY, NULL);
+	if (ret)
+		return ret;
+	drm_plane_helper_add(plane, &hyperv_plane_helper_funcs);
+	drm_plane_enable_fb_damage_clips(plane);
+
+	ret = drm_crtc_init_with_planes(dev, crtc, plane, NULL,
+					&hyperv_crtc_funcs, NULL);
+	if (ret)
+		return ret;
+	drm_crtc_helper_add(crtc, &hyperv_crtc_helper_funcs);
+
+	encoder->possible_crtcs = drm_crtc_mask(crtc);
+	ret = drm_encoder_init(dev, encoder,
+			       &hyperv_drm_simple_encoder_funcs_cleanup,
+			       DRM_MODE_ENCODER_NONE, NULL);
+	if (ret)
+		return ret;
+
+	ret = hyperv_conn_init(hv);
+	if (ret) {
+		drm_err(dev, "Failed to initialized connector.\n");
+		return ret;
+	}
+
+	return drm_connector_attach_encoder(connector, encoder);
+}
+
+static enum drm_mode_status
+hyperv_mode_valid(struct drm_device *dev,
+		  const struct drm_display_mode *mode)
+{
+	struct hyperv_drm_device *hv = to_hv(dev);
+
+	if (hyperv_check_size(hv, mode->hdisplay, mode->vdisplay, NULL))
+		return MODE_BAD;
+
+	return MODE_OK;
+}
+
+static const struct drm_mode_config_funcs hyperv_mode_config_funcs = {
+	.fb_create = drm_gem_fb_create_with_dirty,
+	.mode_valid = hyperv_mode_valid,
+	.atomic_check = drm_atomic_helper_check,
+	.atomic_commit = drm_atomic_helper_commit,
+};
+
+int hyperv_mode_config_init(struct hyperv_drm_device *hv)
+{
+	struct drm_device *dev = &hv->dev;
+	int ret;
+
+	ret = drmm_mode_config_init(dev);
+	if (ret) {
+		drm_err(dev, "Failed to initialized mode setting.\n");
+		return ret;
+	}
+
+	dev->mode_config.min_width = 0;
+	dev->mode_config.min_height = 0;
+	dev->mode_config.max_width = hv->screen_width_max;
+	dev->mode_config.max_height = hv->screen_height_max;
+
+	dev->mode_config.preferred_depth = hv->screen_depth;
+	dev->mode_config.prefer_shadow = 0;
+
+	dev->mode_config.funcs = &hyperv_mode_config_funcs;
+
+	ret = hyperv_pipe_init(hv);
+	if (ret) {
+		drm_err(dev, "Failed to initialized pipe.\n");
+		return ret;
+	}
+
+	ret = drm_vblank_init(dev, 1);
+	if (ret)
+		return ret;
+
+	drm_mode_config_reset(dev);
+
+	return 0;
+}
diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_proto.c b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
new file mode 100644
index 000000000..6e09b0218
--- /dev/null
+++ b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c
@@ -0,0 +1,604 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2021 Microsoft
+ */
+
+#include <linux/hyperv.h>
+
+#include <drm/drm_print.h>
+#include <drm/drm_simple_kms_helper.h>
+
+#include "hyperv_drm.h"
+
+#define VMBUS_RING_BUFSIZE VMBUS_RING_SIZE(256 * 1024)
+#define VMBUS_VSP_TIMEOUT (10 * HZ)
+
+#define SYNTHVID_VERSION(major, minor) ((minor) << 16 | (major))
+#define SYNTHVID_VER_GET_MAJOR(ver) (ver & 0x0000ffff)
+#define SYNTHVID_VER_GET_MINOR(ver) ((ver & 0xffff0000) >> 16)
+
+/* Support for VERSION_WIN7 is removed. #define is retained for reference. */
+#define SYNTHVID_VERSION_WIN7 SYNTHVID_VERSION(3, 0)
+#define SYNTHVID_VERSION_WIN8 SYNTHVID_VERSION(3, 2)
+#define SYNTHVID_VERSION_WIN10 SYNTHVID_VERSION(3, 5)
+
+#define SYNTHVID_DEPTH_WIN8 32
+#define SYNTHVID_WIDTH_WIN8 1600
+#define SYNTHVID_HEIGHT_WIN8 1200
+#define SYNTHVID_FB_SIZE_WIN8 (8 * 1024 * 1024)
+
+enum pipe_msg_type {
+	PIPE_MSG_INVALID,
+	PIPE_MSG_DATA,
+	PIPE_MSG_MAX
+};
+
+enum synthvid_msg_type {
+	SYNTHVID_ERROR			= 0,
+	SYNTHVID_VERSION_REQUEST	= 1,
+	SYNTHVID_VERSION_RESPONSE	= 2,
+	SYNTHVID_VRAM_LOCATION		= 3,
+	SYNTHVID_VRAM_LOCATION_ACK	= 4,
+	SYNTHVID_SITUATION_UPDATE	= 5,
+	SYNTHVID_SITUATION_UPDATE_ACK	= 6,
+	SYNTHVID_POINTER_POSITION	= 7,
+	SYNTHVID_POINTER_SHAPE		= 8,
+	SYNTHVID_FEATURE_CHANGE		= 9,
+	SYNTHVID_DIRT			= 10,
+	SYNTHVID_RESOLUTION_REQUEST	= 13,
+	SYNTHVID_RESOLUTION_RESPONSE	= 14,
+
+	SYNTHVID_MAX			= 15
+};
+
+struct pipe_msg_hdr {
+	u32 type;
+	u32 size; /* size of message after this field */
+} __packed;
+
+struct hvd_screen_info {
+	u16 width;
+	u16 height;
+} __packed;
+
+struct synthvid_msg_hdr {
+	u32 type;
+	u32 size;  /* size of this header + payload after this field */
+} __packed;
+
+struct synthvid_version_req {
+	u32 version;
+} __packed;
+
+struct synthvid_version_resp {
+	u32 version;
+	u8 is_accepted;
+	u8 max_video_outputs;
+} __packed;
+
+struct synthvid_vram_location {
+	u64 user_ctx;
+	u8 is_vram_gpa_specified;
+	u64 vram_gpa;
+} __packed;
+
+struct synthvid_vram_location_ack {
+	u64 user_ctx;
+} __packed;
+
+struct video_output_situation {
+	u8 active;
+	u32 vram_offset;
+	u8 depth_bits;
+	u32 width_pixels;
+	u32 height_pixels;
+	u32 pitch_bytes;
+} __packed;
+
+struct synthvid_situation_update {
+	u64 user_ctx;
+	u8 video_output_count;
+	struct video_output_situation video_output[1];
+} __packed;
+
+struct synthvid_situation_update_ack {
+	u64 user_ctx;
+} __packed;
+
+struct synthvid_pointer_position {
+	u8 is_visible;
+	u8 video_output;
+	s32 image_x;
+	s32 image_y;
+} __packed;
+
+#define SYNTHVID_CURSOR_MAX_X 96
+#define SYNTHVID_CURSOR_MAX_Y 96
+#define SYNTHVID_CURSOR_ARGB_PIXEL_SIZE 4
+#define SYNTHVID_CURSOR_MAX_SIZE (SYNTHVID_CURSOR_MAX_X * \
+	SYNTHVID_CURSOR_MAX_Y * SYNTHVID_CURSOR_ARGB_PIXEL_SIZE)
+#define SYNTHVID_CURSOR_COMPLETE (-1)
+
+struct synthvid_pointer_shape {
+	u8 part_idx;
+	u8 is_argb;
+	u32 width; /* SYNTHVID_CURSOR_MAX_X at most */
+	u32 height; /* SYNTHVID_CURSOR_MAX_Y at most */
+	u32 hot_x; /* hotspot relative to upper-left of pointer image */
+	u32 hot_y;
+	u8 data[4];
+} __packed;
+
+struct synthvid_feature_change {
+	u8 is_dirt_needed;
+	u8 is_ptr_pos_needed;
+	u8 is_ptr_shape_needed;
+	u8 is_situ_needed;
+} __packed;
+
+struct rect {
+	s32 x1, y1; /* top left corner */
+	s32 x2, y2; /* bottom right corner, exclusive */
+} __packed;
+
+struct synthvid_dirt {
+	u8 video_output;
+	u8 dirt_count;
+	struct rect rect[1];
+} __packed;
+
+#define SYNTHVID_EDID_BLOCK_SIZE	128
+#define	SYNTHVID_MAX_RESOLUTION_COUNT	64
+
+struct synthvid_supported_resolution_req {
+	u8 maximum_resolution_count;
+} __packed;
+
+struct synthvid_supported_resolution_resp {
+	u8 edid_block[SYNTHVID_EDID_BLOCK_SIZE];
+	u8 resolution_count;
+	u8 default_resolution_index;
+	u8 is_standard;
+	struct hvd_screen_info supported_resolution[SYNTHVID_MAX_RESOLUTION_COUNT];
+} __packed;
+
+struct synthvid_msg {
+	struct pipe_msg_hdr pipe_hdr;
+	struct synthvid_msg_hdr vid_hdr;
+	union {
+		struct synthvid_version_req ver_req;
+		struct synthvid_version_resp ver_resp;
+		struct synthvid_vram_location vram;
+		struct synthvid_vram_location_ack vram_ack;
+		struct synthvid_situation_update situ;
+		struct synthvid_situation_update_ack situ_ack;
+		struct synthvid_pointer_position ptr_pos;
+		struct synthvid_pointer_shape ptr_shape;
+		struct synthvid_feature_change feature_chg;
+		struct synthvid_dirt dirt;
+		struct synthvid_supported_resolution_req resolution_req;
+		struct synthvid_supported_resolution_resp resolution_resp;
+	};
+} __packed;
+
+static inline bool hyperv_version_ge(u32 ver1, u32 ver2)
+{
+	if (SYNTHVID_VER_GET_MAJOR(ver1) > SYNTHVID_VER_GET_MAJOR(ver2) ||
+	    (SYNTHVID_VER_GET_MAJOR(ver1) == SYNTHVID_VER_GET_MAJOR(ver2) &&
+	     SYNTHVID_VER_GET_MINOR(ver1) >= SYNTHVID_VER_GET_MINOR(ver2)))
+		return true;
+
+	return false;
+}
+
+static inline int hyperv_sendpacket(struct hv_device *hdev, struct synthvid_msg *msg)
+{
+	static atomic64_t request_id = ATOMIC64_INIT(0);
+	struct hyperv_drm_device *hv = hv_get_drvdata(hdev);
+	int ret;
+
+	msg->pipe_hdr.type = PIPE_MSG_DATA;
+	msg->pipe_hdr.size = msg->vid_hdr.size;
+
+	ret = vmbus_sendpacket(hdev->channel, msg,
+			       msg->vid_hdr.size + sizeof(struct pipe_msg_hdr),
+			       atomic64_inc_return(&request_id),
+			       VM_PKT_DATA_INBAND, 0);
+
+	if (ret)
+		drm_err_ratelimited(&hv->dev, "Unable to send packet via vmbus; error %d\n", ret);
+
+	return ret;
+}
+
+static int hyperv_negotiate_version(struct hv_device *hdev, u32 ver)
+{
+	struct hyperv_drm_device *hv = hv_get_drvdata(hdev);
+	struct synthvid_msg *msg = (struct synthvid_msg *)hv->init_buf;
+	struct drm_device *dev = &hv->dev;
+	unsigned long t;
+
+	memset(msg, 0, sizeof(struct synthvid_msg));
+	msg->vid_hdr.type = SYNTHVID_VERSION_REQUEST;
+	msg->vid_hdr.size = sizeof(struct synthvid_msg_hdr) +
+		sizeof(struct synthvid_version_req);
+	msg->ver_req.version = ver;
+	hyperv_sendpacket(hdev, msg);
+
+	t = wait_for_completion_timeout(&hv->wait, VMBUS_VSP_TIMEOUT);
+	if (!t) {
+		drm_err(dev, "Time out on waiting version response\n");
+		return -ETIMEDOUT;
+	}
+
+	if (!msg->ver_resp.is_accepted) {
+		drm_err(dev, "Version request not accepted\n");
+		return -ENODEV;
+	}
+
+	hv->synthvid_version = ver;
+	drm_info(dev, "Synthvid Version major %d, minor %d\n",
+		 SYNTHVID_VER_GET_MAJOR(ver), SYNTHVID_VER_GET_MINOR(ver));
+
+	return 0;
+}
+
+int hyperv_update_vram_location(struct hv_device *hdev, phys_addr_t vram_pp)
+{
+	struct hyperv_drm_device *hv = hv_get_drvdata(hdev);
+	struct synthvid_msg *msg = (struct synthvid_msg *)hv->init_buf;
+	struct drm_device *dev = &hv->dev;
+	unsigned long t;
+
+	memset(msg, 0, sizeof(struct synthvid_msg));
+	msg->vid_hdr.type = SYNTHVID_VRAM_LOCATION;
+	msg->vid_hdr.size = sizeof(struct synthvid_msg_hdr) +
+		sizeof(struct synthvid_vram_location);
+	msg->vram.user_ctx = vram_pp;
+	msg->vram.vram_gpa = vram_pp;
+	msg->vram.is_vram_gpa_specified = 1;
+	hyperv_sendpacket(hdev, msg);
+
+	t = wait_for_completion_timeout(&hv->wait, VMBUS_VSP_TIMEOUT);
+	if (!t) {
+		drm_err(dev, "Time out on waiting vram location ack\n");
+		return -ETIMEDOUT;
+	}
+	if (msg->vram_ack.user_ctx != vram_pp) {
+		drm_err(dev, "Unable to set VRAM location\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+int hyperv_update_situation(struct hv_device *hdev, u8 active, u32 bpp,
+			    u32 w, u32 h, u32 pitch)
+{
+	struct synthvid_msg msg;
+
+	memset(&msg, 0, sizeof(struct synthvid_msg));
+
+	msg.vid_hdr.type = SYNTHVID_SITUATION_UPDATE;
+	msg.vid_hdr.size = sizeof(struct synthvid_msg_hdr) +
+		sizeof(struct synthvid_situation_update);
+	msg.situ.user_ctx = 0;
+	msg.situ.video_output_count = 1;
+	msg.situ.video_output[0].active = active;
+	/* vram_offset should always be 0 */
+	msg.situ.video_output[0].vram_offset = 0;
+	msg.situ.video_output[0].depth_bits = bpp;
+	msg.situ.video_output[0].width_pixels = w;
+	msg.situ.video_output[0].height_pixels = h;
+	msg.situ.video_output[0].pitch_bytes = pitch;
+
+	hyperv_sendpacket(hdev, &msg);
+
+	return 0;
+}
+
+/*
+ * Hyper-V supports a hardware cursor feature. It's not used by Linux VM,
+ * but the Hyper-V host still draws a point as an extra mouse pointer,
+ * which is unwanted, especially when Xorg is running.
+ *
+ * Hide the unwanted pointer, by setting msg.ptr_pos.is_visible = 1 and setting
+ * the msg.ptr_shape.data. Note: setting msg.ptr_pos.is_visible to 0 doesn't
+ * work in tests.
+ *
+ * The hyperv_hide_hw_ptr() is also called in the handler of the
+ * SYNTHVID_FEATURE_CHANGE event, otherwise the host still draws an extra
+ * unwanted mouse pointer after the VM Connection window is closed and reopened.
+ */
+int hyperv_hide_hw_ptr(struct hv_device *hdev)
+{
+	struct synthvid_msg msg;
+
+	memset(&msg, 0, sizeof(struct synthvid_msg));
+	msg.vid_hdr.type = SYNTHVID_POINTER_POSITION;
+	msg.vid_hdr.size = sizeof(struct synthvid_msg_hdr) +
+		sizeof(struct synthvid_pointer_position);
+	msg.ptr_pos.is_visible = 1;
+	msg.ptr_pos.video_output = 0;
+	msg.ptr_pos.image_x = 0;
+	msg.ptr_pos.image_y = 0;
+	hyperv_sendpacket(hdev, &msg);
+
+	memset(&msg, 0, sizeof(struct synthvid_msg));
+	msg.vid_hdr.type = SYNTHVID_POINTER_SHAPE;
+	msg.vid_hdr.size = sizeof(struct synthvid_msg_hdr) +
+		sizeof(struct synthvid_pointer_shape);
+	msg.ptr_shape.part_idx = SYNTHVID_CURSOR_COMPLETE;
+	msg.ptr_shape.is_argb = 1;
+	msg.ptr_shape.width = 1;
+	msg.ptr_shape.height = 1;
+	msg.ptr_shape.hot_x = 0;
+	msg.ptr_shape.hot_y = 0;
+	msg.ptr_shape.data[0] = 0;
+	msg.ptr_shape.data[1] = 1;
+	msg.ptr_shape.data[2] = 1;
+	msg.ptr_shape.data[3] = 1;
+	hyperv_sendpacket(hdev, &msg);
+
+	return 0;
+}
+
+int hyperv_update_dirt(struct hv_device *hdev, struct drm_rect *rect)
+{
+	struct hyperv_drm_device *hv = hv_get_drvdata(hdev);
+	struct synthvid_msg msg;
+
+	if (!hv->dirt_needed)
+		return 0;
+
+	memset(&msg, 0, sizeof(struct synthvid_msg));
+
+	msg.vid_hdr.type = SYNTHVID_DIRT;
+	msg.vid_hdr.size = sizeof(struct synthvid_msg_hdr) +
+		sizeof(struct synthvid_dirt);
+	msg.dirt.video_output = 0;
+	msg.dirt.dirt_count = 1;
+	msg.dirt.rect[0].x1 = rect->x1;
+	msg.dirt.rect[0].y1 = rect->y1;
+	msg.dirt.rect[0].x2 = rect->x2;
+	msg.dirt.rect[0].y2 = rect->y2;
+
+	hyperv_sendpacket(hdev, &msg);
+
+	return 0;
+}
+
+static int hyperv_get_supported_resolution(struct hv_device *hdev)
+{
+	struct hyperv_drm_device *hv = hv_get_drvdata(hdev);
+	struct synthvid_msg *msg = (struct synthvid_msg *)hv->init_buf;
+	struct drm_device *dev = &hv->dev;
+	unsigned long t;
+	u8 index;
+	int i;
+
+	memset(msg, 0, sizeof(struct synthvid_msg));
+	msg->vid_hdr.type = SYNTHVID_RESOLUTION_REQUEST;
+	msg->vid_hdr.size = sizeof(struct synthvid_msg_hdr) +
+		sizeof(struct synthvid_supported_resolution_req);
+	msg->resolution_req.maximum_resolution_count =
+		SYNTHVID_MAX_RESOLUTION_COUNT;
+	hyperv_sendpacket(hdev, msg);
+
+	t = wait_for_completion_timeout(&hv->wait, VMBUS_VSP_TIMEOUT);
+	if (!t) {
+		drm_err(dev, "Time out on waiting resolution response\n");
+		return -ETIMEDOUT;
+	}
+
+	if (msg->resolution_resp.resolution_count == 0 ||
+	    msg->resolution_resp.resolution_count >
+	    SYNTHVID_MAX_RESOLUTION_COUNT) {
+		drm_err(dev, "Invalid resolution count: %d\n",
+			msg->resolution_resp.resolution_count);
+		return -ENODEV;
+	}
+
+	index = msg->resolution_resp.default_resolution_index;
+	if (index >= msg->resolution_resp.resolution_count) {
+		drm_err(dev, "Invalid resolution index: %d\n", index);
+		return -ENODEV;
+	}
+
+	for (i = 0; i < msg->resolution_resp.resolution_count; i++) {
+		hv->screen_width_max = max_t(u32, hv->screen_width_max,
+			msg->resolution_resp.supported_resolution[i].width);
+		hv->screen_height_max = max_t(u32, hv->screen_height_max,
+			msg->resolution_resp.supported_resolution[i].height);
+	}
+
+	hv->preferred_width =
+		msg->resolution_resp.supported_resolution[index].width;
+	hv->preferred_height =
+		msg->resolution_resp.supported_resolution[index].height;
+
+	return 0;
+}
+
+static void hyperv_receive_sub(struct hv_device *hdev, u32 bytes_recvd)
+{
+	struct hyperv_drm_device *hv = hv_get_drvdata(hdev);
+	struct synthvid_msg *msg;
+	size_t hdr_size;
+	size_t need;
+
+	if (!hv)
+		return;
+
+	hdr_size = sizeof(struct pipe_msg_hdr) +
+		   sizeof(struct synthvid_msg_hdr);
+	if (bytes_recvd < hdr_size) {
+		drm_err_ratelimited(&hv->dev,
+				    "synthvid packet too small for header: %u\n",
+				    bytes_recvd);
+		return;
+	}
+
+	msg = (struct synthvid_msg *)hv->recv_buf;
+	need = hdr_size;
+
+	switch (msg->vid_hdr.type) {
+	case SYNTHVID_VERSION_RESPONSE:
+		need += sizeof(struct synthvid_version_resp);
+		break;
+	case SYNTHVID_RESOLUTION_RESPONSE:
+		/*
+		 * The resolution response is variable length: the host
+		 * fills resolution_count entries, not the full
+		 * SYNTHVID_MAX_RESOLUTION_COUNT array. Require the fixed
+		 * prefix first so resolution_count can be read, then
+		 * demand exactly the count-sized array.
+		 */
+		need += offsetof(struct synthvid_supported_resolution_resp,
+				 supported_resolution);
+		if (bytes_recvd < need)
+			break;
+		if (msg->resolution_resp.resolution_count >
+		    SYNTHVID_MAX_RESOLUTION_COUNT) {
+			drm_err_ratelimited(&hv->dev,
+					    "synthvid resolution count too large: %u\n",
+					    msg->resolution_resp.resolution_count);
+			return;
+		}
+		need += msg->resolution_resp.resolution_count *
+			sizeof(struct hvd_screen_info);
+		break;
+	case SYNTHVID_VRAM_LOCATION_ACK:
+		need += sizeof(struct synthvid_vram_location_ack);
+		break;
+	case SYNTHVID_FEATURE_CHANGE:
+		/*
+		 * Not a completion-driving message: validate its own payload
+		 * and consume it here rather than falling through to the
+		 * memcpy/complete shared by the wait-event responses.
+		 */
+		if (bytes_recvd < need +
+		    sizeof(struct synthvid_feature_change)) {
+			drm_err_ratelimited(&hv->dev,
+					    "synthvid feature change packet too small: %u\n",
+					    bytes_recvd);
+			return;
+		}
+		hv->dirt_needed = msg->feature_chg.is_dirt_needed;
+		if (hv->dirt_needed)
+			hyperv_hide_hw_ptr(hv->hdev);
+		return;
+	default:
+		return;
+	}
+
+	/*
+	 * Shared completion path for the wait-event responses
+	 * (VERSION_RESPONSE, RESOLUTION_RESPONSE, VRAM_LOCATION_ACK):
+	 * require the type-specific payload before handing the buffer to
+	 * the waiter.
+	 */
+	if (bytes_recvd < need) {
+		drm_err_ratelimited(&hv->dev,
+				    "synthvid packet too small for type %u: %u < %zu\n",
+				    msg->vid_hdr.type, bytes_recvd, need);
+		return;
+	}
+	memcpy(hv->init_buf, msg, bytes_recvd);
+	complete(&hv->wait);
+}
+
+static void hyperv_receive(void *ctx)
+{
+	struct hv_device *hdev = ctx;
+	struct hyperv_drm_device *hv = hv_get_drvdata(hdev);
+	struct synthvid_msg *recv_buf;
+	u32 bytes_recvd;
+	u64 req_id;
+	int ret;
+
+	if (!hv)
+		return;
+
+	recv_buf = (struct synthvid_msg *)hv->recv_buf;
+
+	do {
+		ret = vmbus_recvpacket(hdev->channel, recv_buf,
+				       VMBUS_MAX_PACKET_SIZE,
+				       &bytes_recvd, &req_id);
+		if (ret) {
+			/*
+			 * A nonzero return (e.g. -ENOBUFS for an oversized
+			 * packet) is itself a malformed message: bytes_recvd
+			 * then reports the required length rather than a copied
+			 * payload, so it must not be forwarded to the
+			 * sub-handler. Channel recovery is not attempted.
+			 */
+			drm_err_ratelimited(&hv->dev,
+					    "vmbus_recvpacket failed: %d (need %u)\n",
+					    ret, bytes_recvd);
+		} else if (bytes_recvd > 0 &&
+			   recv_buf->pipe_hdr.type == PIPE_MSG_DATA) {
+			hyperv_receive_sub(hdev, bytes_recvd);
+		}
+	} while (bytes_recvd > 0 && ret == 0);
+}
+
+int hyperv_connect_vsp(struct hv_device *hdev)
+{
+	struct hyperv_drm_device *hv = hv_get_drvdata(hdev);
+	struct drm_device *dev = &hv->dev;
+	int ret;
+
+	ret = vmbus_open(hdev->channel, VMBUS_RING_BUFSIZE, VMBUS_RING_BUFSIZE,
+			 NULL, 0, hyperv_receive, hdev);
+	if (ret) {
+		drm_err(dev, "Unable to open vmbus channel\n");
+		return ret;
+	}
+
+	/* Negotiate the protocol version with host */
+	switch (vmbus_proto_version) {
+	case VERSION_WIN10:
+	case VERSION_WIN10_V5:
+		ret = hyperv_negotiate_version(hdev, SYNTHVID_VERSION_WIN10);
+		if (!ret)
+			break;
+		fallthrough;
+	case VERSION_WIN8:
+	case VERSION_WIN8_1:
+		ret = hyperv_negotiate_version(hdev, SYNTHVID_VERSION_WIN8);
+		break;
+	default:
+		ret = hyperv_negotiate_version(hdev, SYNTHVID_VERSION_WIN10);
+		break;
+	}
+
+	if (ret) {
+		drm_err(dev, "Synthetic video device version not accepted %d\n", ret);
+		goto error;
+	}
+
+	hv->screen_depth = SYNTHVID_DEPTH_WIN8;
+
+	if (hyperv_version_ge(hv->synthvid_version, SYNTHVID_VERSION_WIN10)) {
+		ret = hyperv_get_supported_resolution(hdev);
+		if (ret)
+			drm_err(dev, "Failed to get supported resolution from host, use default\n");
+	}
+
+	if (!hv->screen_width_max) {
+		hv->screen_width_max = SYNTHVID_WIDTH_WIN8;
+		hv->screen_height_max = SYNTHVID_HEIGHT_WIN8;
+		hv->preferred_width = SYNTHVID_WIDTH_WIN8;
+		hv->preferred_height = SYNTHVID_HEIGHT_WIN8;
+	}
+
+	hv->mmio_megabytes = hdev->channel->offermsg.offer.mmio_megabytes;
+
+	return 0;
+
+error:
+	vmbus_close(hdev->channel);
+	return ret;
+}