--- /dev/null
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_simple_kms_helper.h>
+#include <drm/drm_vblank.h>
+
+#include "amdgpu.h"
+#include "amdgpu_vkms.h"
+#include "amdgpu_display.h"
+
+/**
+ * DOC: amdgpu_vkms
+ *
+ * The amdgpu vkms interface provides a virtual KMS interface for several use
+ * cases: devices without display hardware, platforms where the actual display
+ * hardware is not useful (e.g., servers), SR-IOV virtual functions, device
+ * emulation/simulation, and device bring up prior to display hardware being
+ * usable. We previously emulated a legacy KMS interface, but there was a desire
+ * to move to the atomic KMS interface. The vkms driver did everything we
+ * needed, but we wanted KMS support natively in the driver without buffer
+ * sharing and the ability to support an instance of VKMS per device. We first
+ * looked at splitting vkms into a stub driver and a helper module that other
+ * drivers could use to implement a virtual display, but this strategy ended up
+ * being messy due to driver specific callbacks needed for buffer management.
+ * Ultimately, it proved easier to import the vkms code as it mostly used core
+ * drm helpers anyway.
+ */
+
+static const u32 amdgpu_vkms_formats[] = {
+       DRM_FORMAT_XRGB8888,
+};
+
+static enum hrtimer_restart amdgpu_vkms_vblank_simulate(struct hrtimer *timer)
+{
+       struct amdgpu_vkms_output *output = container_of(timer,
+                                                        struct amdgpu_vkms_output,
+                                                        vblank_hrtimer);
+       struct drm_crtc *crtc = &output->crtc;
+       u64 ret_overrun;
+       bool ret;
+
+       ret_overrun = hrtimer_forward_now(&output->vblank_hrtimer,
+                                         output->period_ns);
+       WARN_ON(ret_overrun != 1);
+
+       ret = drm_crtc_handle_vblank(crtc);
+       if (!ret)
+               DRM_ERROR("amdgpu_vkms failure on handling vblank");
+
+       return HRTIMER_RESTART;
+}
+
+static int amdgpu_vkms_enable_vblank(struct drm_crtc *crtc)
+{
+       struct drm_device *dev = crtc->dev;
+       unsigned int pipe = drm_crtc_index(crtc);
+       struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+       struct amdgpu_vkms_output *out = drm_crtc_to_amdgpu_vkms_output(crtc);
+
+       drm_calc_timestamping_constants(crtc, &crtc->mode);
+
+       hrtimer_init(&out->vblank_hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+       out->vblank_hrtimer.function = &amdgpu_vkms_vblank_simulate;
+       out->period_ns = ktime_set(0, vblank->framedur_ns);
+       hrtimer_start(&out->vblank_hrtimer, out->period_ns, HRTIMER_MODE_REL);
+
+       return 0;
+}
+
+static void amdgpu_vkms_disable_vblank(struct drm_crtc *crtc)
+{
+       struct amdgpu_vkms_output *out = drm_crtc_to_amdgpu_vkms_output(crtc);
+
+       hrtimer_cancel(&out->vblank_hrtimer);
+}
+
+static bool amdgpu_vkms_get_vblank_timestamp(struct drm_crtc *crtc,
+                                            int *max_error,
+                                            ktime_t *vblank_time,
+                                            bool in_vblank_irq)
+{
+       struct drm_device *dev = crtc->dev;
+       unsigned int pipe = crtc->index;
+       struct amdgpu_vkms_output *output = drm_crtc_to_amdgpu_vkms_output(crtc);
+       struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+
+       if (!READ_ONCE(vblank->enabled)) {
+               *vblank_time = ktime_get();
+               return true;
+       }
+
+       *vblank_time = READ_ONCE(output->vblank_hrtimer.node.expires);
+
+       if (WARN_ON(*vblank_time == vblank->time))
+               return true;
+
+       /*
+        * To prevent races we roll the hrtimer forward before we do any
+        * interrupt processing - this is how real hw works (the interrupt is
+        * only generated after all the vblank registers are updated) and what
+        * the vblank core expects. Therefore we need to always correct the
+        * timestampe by one frame.
+        */
+       *vblank_time -= output->period_ns;
+
+       return true;
+}
+
+static const struct drm_crtc_funcs amdgpu_vkms_crtc_funcs = {
+       .set_config             = drm_atomic_helper_set_config,
+       .destroy                = drm_crtc_cleanup,
+       .page_flip              = drm_atomic_helper_page_flip,
+       .reset                  = drm_atomic_helper_crtc_reset,
+       .atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
+       .atomic_destroy_state   = drm_atomic_helper_crtc_destroy_state,
+       .enable_vblank          = amdgpu_vkms_enable_vblank,
+       .disable_vblank         = amdgpu_vkms_disable_vblank,
+       .get_vblank_timestamp   = amdgpu_vkms_get_vblank_timestamp,
+};
+
+static void amdgpu_vkms_crtc_atomic_enable(struct drm_crtc *crtc,
+                                          struct drm_atomic_state *state)
+{
+       drm_crtc_vblank_on(crtc);
+}
+
+static void amdgpu_vkms_crtc_atomic_disable(struct drm_crtc *crtc,
+                                           struct drm_atomic_state *state)
+{
+       drm_crtc_vblank_off(crtc);
+}
+
+static void amdgpu_vkms_crtc_atomic_flush(struct drm_crtc *crtc,
+                                         struct drm_atomic_state *state)
+{
+       if (crtc->state->event) {
+               spin_lock(&crtc->dev->event_lock);
+
+               if (drm_crtc_vblank_get(crtc) != 0)
+                       drm_crtc_send_vblank_event(crtc, crtc->state->event);
+               else
+                       drm_crtc_arm_vblank_event(crtc, crtc->state->event);
+
+               spin_unlock(&crtc->dev->event_lock);
+
+               crtc->state->event = NULL;
+       }
+}
+
+static const struct drm_crtc_helper_funcs amdgpu_vkms_crtc_helper_funcs = {
+       .atomic_flush   = amdgpu_vkms_crtc_atomic_flush,
+       .atomic_enable  = amdgpu_vkms_crtc_atomic_enable,
+       .atomic_disable = amdgpu_vkms_crtc_atomic_disable,
+};
+
+static int amdgpu_vkms_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
+                         struct drm_plane *primary, struct drm_plane *cursor)
+{
+       int ret;
+
+       ret = drm_crtc_init_with_planes(dev, crtc, primary, cursor,
+                                       &amdgpu_vkms_crtc_funcs, NULL);
+       if (ret) {
+               DRM_ERROR("Failed to init CRTC\n");
+               return ret;
+       }
+
+       drm_crtc_helper_add(crtc, &amdgpu_vkms_crtc_helper_funcs);
+
+       return ret;
+}
+
+static const struct drm_connector_funcs amdgpu_vkms_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 int amdgpu_vkms_conn_get_modes(struct drm_connector *connector)
+{
+       struct drm_device *dev = connector->dev;
+       struct drm_display_mode *mode = NULL;
+       unsigned i;
+       static const struct mode_size {
+               int w;
+               int h;
+       } common_modes[] = {
+               { 640,  480},
+               { 720,  480},
+               { 800,  600},
+               { 848,  480},
+               {1024,  768},
+               {1152,  768},
+               {1280,  720},
+               {1280,  800},
+               {1280,  854},
+               {1280,  960},
+               {1280, 1024},
+               {1440,  900},
+               {1400, 1050},
+               {1680, 1050},
+               {1600, 1200},
+               {1920, 1080},
+               {1920, 1200},
+               {2560, 1440},
+               {4096, 3112},
+               {3656, 2664},
+               {3840, 2160},
+               {4096, 2160},
+       };
+
+       for (i = 0; i < ARRAY_SIZE(common_modes); i++) {
+               mode = drm_cvt_mode(dev, common_modes[i].w, common_modes[i].h, 60, false, false, false);
+               drm_mode_probed_add(connector, mode);
+       }
+
+       drm_set_preferred_mode(connector, XRES_DEF, YRES_DEF);
+
+       return ARRAY_SIZE(common_modes);
+}
+
+static const struct drm_connector_helper_funcs amdgpu_vkms_conn_helper_funcs = {
+       .get_modes    = amdgpu_vkms_conn_get_modes,
+};
+
+static const struct drm_plane_funcs amdgpu_vkms_plane_funcs = {
+       .update_plane           = drm_atomic_helper_update_plane,
+       .disable_plane          = drm_atomic_helper_disable_plane,
+       .destroy                = drm_plane_cleanup,
+       .reset                  = drm_atomic_helper_plane_reset,
+       .atomic_duplicate_state = drm_atomic_helper_plane_duplicate_state,
+       .atomic_destroy_state   = drm_atomic_helper_plane_destroy_state,
+};
+
+static void amdgpu_vkms_plane_atomic_update(struct drm_plane *plane,
+                                           struct drm_atomic_state *old_state)
+{
+       return;
+}
+
+static int amdgpu_vkms_plane_atomic_check(struct drm_plane *plane,
+                                         struct drm_atomic_state *state)
+{
+       struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(state,
+                                                                                plane);
+       struct drm_crtc_state *crtc_state;
+       int ret;
+
+       if (!new_plane_state->fb || WARN_ON(!new_plane_state->crtc))
+               return 0;
+
+       crtc_state = drm_atomic_get_crtc_state(state,
+                                              new_plane_state->crtc);
+       if (IS_ERR(crtc_state))
+               return PTR_ERR(crtc_state);
+
+       ret = drm_atomic_helper_check_plane_state(new_plane_state, crtc_state,
+                                                 DRM_PLANE_HELPER_NO_SCALING,
+                                                 DRM_PLANE_HELPER_NO_SCALING,
+                                                 false, true);
+       if (ret != 0)
+               return ret;
+
+       /* for now primary plane must be visible and full screen */
+       if (!new_plane_state->visible)
+               return -EINVAL;
+
+       return 0;
+}
+
+static int amdgpu_vkms_prepare_fb(struct drm_plane *plane,
+                                 struct drm_plane_state *new_state)
+{
+       struct amdgpu_framebuffer *afb;
+       struct drm_gem_object *obj;
+       struct amdgpu_device *adev;
+       struct amdgpu_bo *rbo;
+       struct list_head list;
+       struct ttm_validate_buffer tv;
+       struct ww_acquire_ctx ticket;
+       uint32_t domain;
+       int r;
+
+       if (!new_state->fb) {
+               DRM_DEBUG_KMS("No FB bound\n");
+               return 0;
+       }
+       afb = to_amdgpu_framebuffer(new_state->fb);
+       obj = new_state->fb->obj[0];
+       rbo = gem_to_amdgpu_bo(obj);
+       adev = amdgpu_ttm_adev(rbo->tbo.bdev);
+       INIT_LIST_HEAD(&list);
+
+       tv.bo = &rbo->tbo;
+       tv.num_shared = 1;
+       list_add(&tv.head, &list);
+
+       r = ttm_eu_reserve_buffers(&ticket, &list, false, NULL);
+       if (r) {
+               dev_err(adev->dev, "fail to reserve bo (%d)\n", r);
+               return r;
+       }
+
+       if (plane->type != DRM_PLANE_TYPE_CURSOR)
+               domain = amdgpu_display_supported_domains(adev, rbo->flags);
+       else
+               domain = AMDGPU_GEM_DOMAIN_VRAM;
+
+       r = amdgpu_bo_pin(rbo, domain);
+       if (unlikely(r != 0)) {
+               if (r != -ERESTARTSYS)
+                       DRM_ERROR("Failed to pin framebuffer with error %d\n", r);
+               ttm_eu_backoff_reservation(&ticket, &list);
+               return r;
+       }
+
+       r = amdgpu_ttm_alloc_gart(&rbo->tbo);
+       if (unlikely(r != 0)) {
+               amdgpu_bo_unpin(rbo);
+               ttm_eu_backoff_reservation(&ticket, &list);
+               DRM_ERROR("%p bind failed\n", rbo);
+               return r;
+       }
+
+       ttm_eu_backoff_reservation(&ticket, &list);
+
+       afb->address = amdgpu_bo_gpu_offset(rbo);
+
+       amdgpu_bo_ref(rbo);
+
+       return 0;
+}
+
+static void amdgpu_vkms_cleanup_fb(struct drm_plane *plane,
+                                  struct drm_plane_state *old_state)
+{
+       struct amdgpu_bo *rbo;
+       int r;
+
+       if (!old_state->fb)
+               return;
+
+       rbo = gem_to_amdgpu_bo(old_state->fb->obj[0]);
+       r = amdgpu_bo_reserve(rbo, false);
+       if (unlikely(r)) {
+               DRM_ERROR("failed to reserve rbo before unpin\n");
+               return;
+       }
+
+       amdgpu_bo_unpin(rbo);
+       amdgpu_bo_unreserve(rbo);
+       amdgpu_bo_unref(&rbo);
+}
+
+static const struct drm_plane_helper_funcs amdgpu_vkms_primary_helper_funcs = {
+       .atomic_update          = amdgpu_vkms_plane_atomic_update,
+       .atomic_check           = amdgpu_vkms_plane_atomic_check,
+       .prepare_fb             = amdgpu_vkms_prepare_fb,
+       .cleanup_fb             = amdgpu_vkms_cleanup_fb,
+};
+
+static struct drm_plane *amdgpu_vkms_plane_init(struct drm_device *dev,
+                                               enum drm_plane_type type,
+                                               int index)
+{
+       struct drm_plane *plane;
+       int ret;
+
+       plane = kzalloc(sizeof(*plane), GFP_KERNEL);
+       if (!plane)
+               return ERR_PTR(-ENOMEM);
+
+       ret = drm_universal_plane_init(dev, plane, 1 << index,
+                                      &amdgpu_vkms_plane_funcs,
+                                      amdgpu_vkms_formats,
+                                      ARRAY_SIZE(amdgpu_vkms_formats),
+                                      NULL, type, NULL);
+       if (ret) {
+               kfree(plane);
+               return ERR_PTR(ret);
+       }
+
+       drm_plane_helper_add(plane, &amdgpu_vkms_primary_helper_funcs);
+
+       return plane;
+}
+
+int amdgpu_vkms_output_init(struct drm_device *dev,
+                           struct amdgpu_vkms_output *output, int index)
+{
+       struct drm_connector *connector = &output->connector;
+       struct drm_encoder *encoder = &output->encoder;
+       struct drm_crtc *crtc = &output->crtc;
+       struct drm_plane *primary, *cursor = NULL;
+       int ret;
+
+       primary = amdgpu_vkms_plane_init(dev, DRM_PLANE_TYPE_PRIMARY, index);
+       if (IS_ERR(primary))
+               return PTR_ERR(primary);
+
+       ret = amdgpu_vkms_crtc_init(dev, crtc, primary, cursor);
+       if (ret)
+               goto err_crtc;
+
+       ret = drm_connector_init(dev, connector, &amdgpu_vkms_connector_funcs,
+                                DRM_MODE_CONNECTOR_VIRTUAL);
+       if (ret) {
+               DRM_ERROR("Failed to init connector\n");
+               goto err_connector;
+       }
+
+       drm_connector_helper_add(connector, &amdgpu_vkms_conn_helper_funcs);
+
+       ret = drm_simple_encoder_init(dev, encoder, DRM_MODE_ENCODER_VIRTUAL);
+       if (ret) {
+               DRM_ERROR("Failed to init encoder\n");
+               goto err_encoder;
+       }
+       encoder->possible_crtcs = 1 << index;
+
+       ret = drm_connector_attach_encoder(connector, encoder);
+       if (ret) {
+               DRM_ERROR("Failed to attach connector to encoder\n");
+               goto err_attach;
+       }
+
+       drm_mode_config_reset(dev);
+
+       return 0;
+
+err_attach:
+       drm_encoder_cleanup(encoder);
+
+err_encoder:
+       drm_connector_cleanup(connector);
+
+err_connector:
+       drm_crtc_cleanup(crtc);
+
+err_crtc:
+       drm_plane_cleanup(primary);
+
+       return ret;
+}