path: root/0031-dri2-add-support-for-swap-intervals-other-than-1.patch

From d1fc3980c459dbef9eaed430800fdd07c5b084d6 Mon Sep 17 00:00:00 2001
From: Luigi Santivetti <luigi.santivetti@imgtec.com>
Date: Wed, 19 Jun 2019 16:36:06 +0100
Subject: [PATCH] dri2: add support for swap intervals other than 1

Before this change, the swap interval was fixed at 1, with page flips
scheduled on the next vblank. This change allows any swap interval
between 0 and 10 to be set.

An additional thread is created, so as not to rely on the application
polling for previously scheduled drm events (be it a flip or a vblank).
Instead, each call to swap buffers made by the application will be
queued, and consumed asynchronously by the additional thread. This
ensures that drm events will be handled as soon as possible,
regardless of the timing of subsequent calls to swap buffers.

Change-Id: If7c0495df7ddfaa08583a14f820c46e1b97da788
Signed-off-by: Luigi Santivetti <luigi.santivetti@imgtec.com>

---
 src/egl/drivers/dri2/egl_dri2.h      |  42 ++-
 src/egl/drivers/dri2/platform_null.c | 541 +++++++++++++++++++++++----
 2 files changed, 506 insertions(+), 77 deletions(-)

diff --git a/src/egl/drivers/dri2/egl_dri2.h b/src/egl/drivers/dri2/egl_dri2.h
index 5de5f0f..f74ee28 100644
--- a/src/egl/drivers/dri2/egl_dri2.h
+++ b/src/egl/drivers/dri2/egl_dri2.h
@@ -328,6 +328,25 @@ struct dri2_egl_context
    __DRIcontext *dri_context;
 };
 
+#define DRI2_SURFACE_NUM_COLOR_BUFFERS 4
+
+#ifdef HAVE_NULL_PLATFORM
+struct swap_queue_elem
+{
+   uint32_t             swap_interval;
+   uint32_t             back_id;
+   uint32_t             fb_id;
+};
+
+enum {
+   SWAP_IDLE,
+   SWAP_FLIP,
+   SWAP_VBLANK,
+   SWAP_POLL,
+   SWAP_ERROR,
+};
+#endif
+
 struct dri2_egl_surface
 {
    _EGLSurface base;
@@ -368,6 +387,19 @@ struct dri2_egl_surface
    struct gbm_dri_surface *gbm_surf;
 #endif
 
+#if defined(HAVE_NULL_PLATFORM)
+   /*
+    * Protects swap_queue_idx_head, swap_queue_idx_tail and
+    * color_buffers.locked.
+    */
+   pthread_mutex_t        mutex;
+   pthread_cond_t         swap_queue_cond;
+   pthread_cond_t         swap_unlock_buffer_cond;
+   int                    swap_queue_idx_head;
+   int                    swap_queue_idx_tail;
+   pthread_t              swap_queue_processor;
+#endif
+
    /* EGL-owned buffers */
    __DRIbuffer *local_buffers[__DRI_BUFFER_COUNT];
 
@@ -394,7 +426,7 @@ struct dri2_egl_surface
 #endif
       bool locked;
       int age;
-   } color_buffers[4], *back, *current;
+   } color_buffers[DRI2_SURFACE_NUM_COLOR_BUFFERS], *back, *current;
 #endif
 
 #ifdef HAVE_ANDROID_PLATFORM
@@ -428,7 +460,13 @@ struct dri2_egl_surface
 #endif
 
 #ifdef HAVE_NULL_PLATFORM
-   uint32_t             front_fb_id;
+   uint32_t                front_fb_id;
+   struct swap_queue_elem  swap_queue[DRI2_SURFACE_NUM_COLOR_BUFFERS];
+   struct swap_queue_elem  *swap_data;
+   int                     swap_state;
+   bool                    mutex_init;
+   bool                    cond_init;
+   bool                    cond_init_unlock_buffer;
 #endif
 
    int out_fence_fd;
diff --git a/src/egl/drivers/dri2/platform_null.c b/src/egl/drivers/dri2/platform_null.c
index fb03ecc..5b7c1ec 100644
--- a/src/egl/drivers/dri2/platform_null.c
+++ b/src/egl/drivers/dri2/platform_null.c
@@ -31,6 +31,7 @@
 #include <drm_fourcc.h>
 #include <fcntl.h>
 #include <poll.h>
+#include <pthread.h>
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdlib.h>
@@ -58,6 +59,17 @@ struct object_property {
    uint64_t prop_value;
 };
 
+static inline
+uint32_t get_back_buffer_id(struct dri2_egl_surface *dri2_surf)
+{
+   uintptr_t offset = ((uintptr_t) dri2_surf->back) -
+      ((uintptr_t) &dri2_surf->color_buffers[0]);
+
+   assert(dri2_surf->back && !(offset >> 32));
+
+   return (uint32_t) (offset / sizeof(dri2_surf->color_buffers[0]));
+}
+
 #define object_property_set_named(output, object_type, prop_name, value)    \
    {                                                                        \
       .object_id = (output)->object_type##_id,                              \
@@ -176,36 +188,6 @@ property_id_get_for_name(drmModePropertyRes **prop_res, const char *prop_name)
    return 0;
 }
 
-static void
-flip_handler(int fd, unsigned int sequence, unsigned int tv_sec,
-             unsigned int tv_usec, void *user_data)
-{
-   bool *plocked = user_data;
-
-   if (plocked)
-      *plocked = false;
-}
-
-static bool
-flip_process(int fd)
-{
-   static drmEventContext evctx =
-      {.version = 2, .page_flip_handler = flip_handler};
-   struct pollfd pfd = {.fd = fd, .events = POLLIN};
-   int ret;
-
-   do {
-      ret = poll(&pfd, 1, -1);
-   } while (ret > 0 && pfd.revents != pfd.events);
-
-   if (ret <= 0)
-      return false;
-
-   drmHandleEvent(fd, &evctx);
-
-   return true;
-}
-
 static drmModePropertyRes **
 object_get_property_resources(int fd, uint32_t object_id, uint32_t object_type)
 {
@@ -495,6 +477,113 @@ display_output_atomic_modeset(int fd, struct display_output *output, uint32_t fb
                               DRM_MODE_ATOMIC_ALLOW_MODESET, NULL);
 }
 
+static void
+swap_enqueue_data(struct dri2_egl_surface *dri2_surf, uint32_t back_id,
+                  uint32_t interval)
+{
+   struct swap_queue_elem *swap_data;
+
+   pthread_mutex_lock(&dri2_surf->mutex);
+   swap_data = &dri2_surf->swap_queue[dri2_surf->swap_queue_idx_tail];
+   swap_data->swap_interval = interval;
+   swap_data->fb_id = dri2_surf->back->fb_id;
+   swap_data->back_id = back_id;
+
+   dri2_surf->swap_queue_idx_tail++;
+   dri2_surf->swap_queue_idx_tail %= ARRAY_SIZE(dri2_surf->swap_queue);
+
+   /* Notify the swap thread there is new work to do */
+   pthread_cond_signal(&dri2_surf->swap_queue_cond);
+   pthread_mutex_unlock(&dri2_surf->mutex);
+}
+
+static void
+swap_dequeue_data_start(struct dri2_egl_surface *dri2_surf)
+{
+   pthread_mutex_lock(&dri2_surf->mutex);
+   while (dri2_surf->swap_queue_idx_head == dri2_surf->swap_queue_idx_tail)
+      pthread_cond_wait(&dri2_surf->swap_queue_cond, &dri2_surf->mutex);
+
+   dri2_surf->swap_data =
+      &dri2_surf->swap_queue[dri2_surf->swap_queue_idx_head];
+   pthread_mutex_unlock(&dri2_surf->mutex);
+}
+
+static void
+swap_dequeue_data_finish(struct dri2_egl_surface *dri2_surf)
+{
+   pthread_mutex_lock(&dri2_surf->mutex);
+
+   if (dri2_surf->current)
+      dri2_surf->current->locked = false;
+
+   dri2_surf->current =
+      &dri2_surf->color_buffers[dri2_surf->swap_data->back_id];
+   dri2_surf->swap_state = SWAP_IDLE;
+
+   dri2_surf->swap_queue_idx_head++;
+   dri2_surf->swap_queue_idx_head %= ARRAY_SIZE(dri2_surf->swap_queue);
+
+   /* Notify get_back_bo that a buffer has become available */
+   pthread_cond_signal(&dri2_surf->swap_unlock_buffer_cond);
+   pthread_mutex_unlock(&dri2_surf->mutex);
+}
+
+static void
+flip_handler(int fd, unsigned int sequence, unsigned int tv_sec,
+             unsigned int tv_usec, void *flip_data)
+{
+   struct dri2_egl_surface *dri2_surf = flip_data;
+
+   (void) tv_sec;
+   (void) tv_usec;
+   (void) sequence;
+
+   /* Ultimate queueing ops */
+   swap_dequeue_data_finish(dri2_surf);
+}
+
+static void
+vblank_handler(int fd, unsigned int sequence, unsigned int tv_sec,
+               unsigned int tv_usec, void *vblank_data)
+{
+   struct dri2_egl_surface *dri2_surf = vblank_data;
+
+   (void) tv_sec;
+   (void) tv_usec;
+   (void) sequence;
+
+   dri2_surf->swap_state = SWAP_FLIP;
+}
+
+static int
+drm_event_process(int fd)
+{
+   static drmEventContext evctx = {
+      .version = 2,
+      .page_flip_handler = flip_handler,
+      .vblank_handler = vblank_handler
+   };
+   struct pollfd pfd = {.fd = fd, .events = POLLIN};
+   int ret;
+
+   do {
+      ret = poll(&pfd, 1, -1);
+   } while (ret > 0 && pfd.revents != pfd.events);
+
+   if (ret <= 0)
+      /* Man says:
+       *
+       * On error, -1 is returned, and errno is set to indicate the
+       * cause of the error.
+       */
+      return -1;
+
+   drmHandleEvent(fd, &evctx);
+
+   return 0;
+}
+
 static bool
 display_output_init(int fd, struct display_output *output, bool use_atomic)
 {
@@ -571,10 +660,46 @@ static int
 display_output_flip(int fd, struct display_output *output, uint32_t fb_id,
                     uint32_t flags, void *flip_data)
 {
-   if (output->atomic_state)
-      return display_output_atomic_flip(fd, output, fb_id, flags, flip_data);
+   int err;
+
+   do {
+      if (output->atomic_state)
+         err = display_output_atomic_flip(fd, output, fb_id, flags, flip_data);
+      else
+         err = drmModePageFlip(fd, output->crtc_id, fb_id, flags, flip_data);
+   } while (err == -EBUSY);
+
+   return err;
+}
+
+static int
+display_request_vblank(int fd, uint32_t target_frame, uint32_t flags,
+                       void *vblank_data)
+{
+   drmVBlank vblank = {
+      .request = {
+         .type = flags,
+         .sequence = target_frame,
+         .signal = (unsigned long)vblank_data,
+      }
+   };
+
+   return drmWaitVBlank(fd, &vblank);
+}
+
+static int
+display_get_vblank_sequence(int fd, uint32_t *current_vblank_out)
+{
+   drmVBlank vblank = { .request = { .type = DRM_VBLANK_RELATIVE } };
+   int err;
+
+   err = drmWaitVBlank(fd, &vblank);
+   if (err)
+      return err;
 
-   return drmModePageFlip(fd, output->crtc_id, fb_id, flags, flip_data);
+   *current_vblank_out = vblank.reply.sequence;
+
+   return 0;
 }
 
 static int
@@ -587,6 +712,213 @@ display_output_modeset(int fd, struct display_output *output, uint32_t fb_id)
                          &output->connector_id, 1, &output->mode);
 }
 
+static int
+swap_idle_get_target_frame(struct dri2_egl_surface *dri2_surf,
+                           uint32_t *current_vblank_out, uint32_t *target_frame_out)
+{
+   struct dri2_egl_display *dri2_dpy =
+      dri2_egl_display(dri2_surf->base.Resource.Display);
+   int err;
+
+   /* For intarvals bigger than 1, always update current_vblank. The
+    * spec isn't fully clear, nonetheless page 25 and 26 of the PDF of the
+    * EGL 1.5 spec say:
+    *
+    *     "[the parameter interval] indicates the number of swap intervals
+    *      that will elapse before a buffer swap takes place after calling
+    *      eglSwapBuffers."
+    *
+    * We need to guarantee that the target frame is always ahead of the
+    * current vblank by the number of intervals set at the time swapBuffer
+    * is called. For intervals of 1 or 0, we don't need a target frame.
+    */
+   err = display_get_vblank_sequence(dri2_dpy->fd, current_vblank_out);
+   if (err)
+      return err;
+
+   assert(dri2_surf->swap_data->swap_interval > 0);
+
+   /* -1 accounts for vsync locked flip, so get a vblank one frame earlier */
+   *target_frame_out =
+      *current_vblank_out + dri2_surf->swap_data->swap_interval - 1;
+
+   return 0;
+}
+
+static int
+swap_idle_state_transition(struct dri2_egl_surface *dri2_surf,
+                           uint32_t *target_frame_out)
+{
+   uint32_t current_vblank = 0;
+   uint32_t target_frame = 0;
+   int err;
+
+   /* update dri2_surf->swap_data */
+   swap_dequeue_data_start(dri2_surf);
+
+   /* update next target frame */
+   if (dri2_surf->swap_data->swap_interval > 1) {
+      err = swap_idle_get_target_frame(dri2_surf, &current_vblank,
+                                       &target_frame);
+      if (err) {
+         dri2_surf->swap_state = SWAP_ERROR;
+         return err;
+      }
+   }
+
+   dri2_surf->swap_state =
+      target_frame <= current_vblank ? SWAP_FLIP : SWAP_VBLANK;
+   *target_frame_out = target_frame;
+
+   return 0;
+}
+
+static int
+swap_vblank_state_transition(struct dri2_egl_surface *dri2_surf,
+                             uint32_t target_frame)
+{
+   struct dri2_egl_display *dri2_dpy =
+      dri2_egl_display(dri2_surf->base.Resource.Display);
+   uint32_t flags = DRM_VBLANK_ABSOLUTE | DRM_VBLANK_EVENT;
+   int err;
+
+   err = display_request_vblank(dri2_dpy->fd, target_frame,
+                                flags, dri2_surf);
+   if (err) {
+      dri2_surf->swap_state = SWAP_ERROR;
+      return err;
+   }
+
+   dri2_surf->swap_state = SWAP_POLL;
+
+   return 0;
+}
+
+static int
+swap_flip_state_transition(struct dri2_egl_surface *dri2_surf)
+{
+   struct dri2_egl_display *dri2_dpy =
+      dri2_egl_display(dri2_surf->base.Resource.Display);
+   uint32_t flags;
+   int err;
+
+   flags = DRM_MODE_PAGE_FLIP_EVENT;
+   if (dri2_surf->swap_data->swap_interval == 0) {
+      assert(!dri2_dpy->atomic_enabled);
+      flags |= DRM_MODE_PAGE_FLIP_ASYNC;
+   }
+
+   err = display_output_flip(dri2_dpy->fd, &dri2_dpy->output,
+                             dri2_surf->swap_data->fb_id, flags, dri2_surf);
+   if (err) {
+      dri2_surf->swap_state = SWAP_ERROR;
+      return err;
+   }
+
+   dri2_surf->swap_state = SWAP_POLL;
+
+   return 0;
+}
+
+static int
+swap_poll_state_transition(struct dri2_egl_surface *dri2_surf)
+{
+   struct dri2_egl_display *dri2_dpy =
+      dri2_egl_display(dri2_surf->base.Resource.Display);
+   int err;
+
+   /* dri2_surf->swap_state is being set inside the handler */
+   err = drm_event_process(dri2_dpy->fd);
+   if (err) {
+      dri2_surf->swap_state = SWAP_ERROR;
+      return err;
+   }
+
+   return 0;
+}
+
+static inline void
+swap_error_print_message(const int state, const int err)
+{
+   switch (state) {
+   case SWAP_IDLE:
+      _eglLog(_EGL_WARNING,
+              "failed to get a target frame (err=%d)", err);
+      break;
+   case SWAP_FLIP:
+      _eglLog(_EGL_WARNING,
+              "failed to schedule a pageflip (err=%d)", err);
+      break;
+   case SWAP_VBLANK:
+      _eglLog(_EGL_WARNING,
+              "failed to request a vblank event (err=%d)", err);
+      break;
+   case SWAP_POLL:
+      _eglLog(_EGL_WARNING,
+              "failed to poll for drm event (err=%d)", err);
+      break;
+   case SWAP_ERROR:
+      _eglLog(_EGL_WARNING,
+              "failed to swap buffers, unknown swap state");
+      break;
+   default:
+      _eglLog(_EGL_FATAL,
+              "failed to swap buffers (unknown error)");
+   };
+}
+
+static void
+swap_error_state_handler(struct dri2_egl_surface *dri2_surf,
+                         int state, int err)
+{
+   static bool do_log = true;
+
+   if (do_log) {
+      swap_error_print_message(state, err);
+      do_log = false;
+   }
+
+   swap_dequeue_data_finish(dri2_surf);
+}
+
+static void *
+swap_queue_processor_worker(void *data)
+{
+   struct dri2_egl_surface *dri2_surf = data;
+   int state = SWAP_IDLE, err = SWAP_ERROR;
+   uint32_t target_frame = 0;
+
+   assert(dri2_surf->swap_state == SWAP_IDLE);
+
+   while (1) {
+      switch (dri2_surf->swap_state) {
+      case SWAP_IDLE:
+         err = swap_idle_state_transition(dri2_surf, &target_frame);
+         break;
+      case SWAP_VBLANK:
+         err = swap_vblank_state_transition(dri2_surf, target_frame);
+         break;
+      case SWAP_FLIP:
+         err = swap_flip_state_transition(dri2_surf);
+         break;
+      case SWAP_POLL:
+         err = swap_poll_state_transition(dri2_surf);
+         break;
+      case SWAP_ERROR:
+         swap_error_state_handler(dri2_surf, state, err);
+         break;
+      default:
+         dri2_surf->swap_state = SWAP_ERROR;
+         break;
+      }
+
+      if (!err)
+         state = dri2_surf->swap_state;
+   }
+
+   return NULL;
+}
+
 static bool
 add_fb_for_dri_image(struct dri2_egl_display *dri2_dpy, __DRIimage *image,
                      uint32_t *fb_id_out)
@@ -651,15 +983,18 @@ get_back_bo(struct dri2_egl_surface *dri2_surf)
    struct dri2_egl_display *dri2_dpy =
       dri2_egl_display(dri2_surf->base.Resource.Display);
 
-   if (!dri2_surf->back) {
+   pthread_mutex_lock(&dri2_surf->mutex);
+   while (!dri2_surf->back) {
       for (unsigned i = 0; i < ARRAY_SIZE(dri2_surf->color_buffers); i++) {
          if (!dri2_surf->color_buffers[i].locked) {
             dri2_surf->back = &dri2_surf->color_buffers[i];
             break;
          }
       }
+
+      /* Wait for a flip to get a buffer off the screen and unlock it */
       if (!dri2_surf->back)
-         return false;
+         pthread_cond_wait(&dri2_surf->swap_unlock_buffer_cond, &dri2_surf->mutex);
    }
 
    if (!dri2_surf->back->dri_image) {
@@ -671,19 +1006,23 @@ get_back_bo(struct dri2_egl_surface *dri2_surf)
                                       __DRI_IMAGE_USE_SCANOUT,
                                       NULL);
       if (!dri2_surf->back->dri_image)
-         return false;
+         goto err_unlock;
    }
 
    if (!dri2_surf->back->fb_id) {
       if (!add_fb_for_dri_image(dri2_dpy, dri2_surf->back->dri_image,
-                                &dri2_surf->back->fb_id)) {
-         return false;
-      }
+                                &dri2_surf->back->fb_id))
+         goto err_unlock;
    }
 
    dri2_surf->back->locked = 1;
+   pthread_mutex_unlock(&dri2_surf->mutex);
 
    return true;
+
+err_unlock:
+   pthread_mutex_unlock(&dri2_surf->mutex);
+   return false;
 }
 
 static _EGLSurface *
@@ -770,6 +1109,26 @@ dri2_null_create_window_surface(_EGLDisplay *disp, _EGLConfig *config,
    dri2_surf->base.Width = dri2_dpy->output.mode.hdisplay;
    dri2_surf->base.Height = dri2_dpy->output.mode.vdisplay;
 
+   /* After the dri2_surf is created, init thread's data */
+   dri2_surf->mutex_init = !pthread_mutex_init(&dri2_surf->mutex, NULL);
+   if (!dri2_surf->mutex_init) {
+      _eglError(EGL_BAD_ALLOC, "failed to init swap thread mutex");
+      goto err_destroy_surface;
+   }
+
+   dri2_surf->cond_init = !pthread_cond_init(&dri2_surf->swap_queue_cond, NULL);
+   if (!dri2_surf->cond_init) {
+      _eglError(EGL_BAD_ALLOC, "failed to init swap queue condition");
+      goto err_destroy_surface;
+   }
+
+   dri2_surf->cond_init_unlock_buffer =
+      !pthread_cond_init(&dri2_surf->swap_unlock_buffer_cond, NULL);
+   if (!dri2_surf->cond_init_unlock_buffer) {
+      _eglError(EGL_BAD_ALLOC, "failed to init swap buffer unlock condition");
+      goto err_destroy_surface;
+   }
+
    if (!get_front_bo(dri2_surf))  {
       _eglError(EGL_BAD_NATIVE_WINDOW, "window get buffer");
       goto err_destroy_surface;
@@ -783,6 +1142,14 @@ dri2_null_create_window_surface(_EGLDisplay *disp, _EGLConfig *config,
    }
 
    dri2_dpy->output.in_use = true;
+   dri2_surf->swap_state = SWAP_IDLE;
+
+   err = pthread_create(&dri2_surf->swap_queue_processor, NULL,
+                        swap_queue_processor_worker, dri2_surf);
+   if (err) {
+      _eglError(EGL_BAD_ALLOC, "failed to create swap thread");
+      goto err_destroy_surface;
+   }
 
    return surf;
 
@@ -808,8 +1175,27 @@ dri2_null_destroy_surface(_EGLDisplay *disp, _EGLSurface *surf)
    /* If there's a current surface then a page flip has been performed, so make
     * sure we process the flip event.
     */
-   if (dri2_surf->current)
-      flip_process(dri2_dpy->fd);
+   if (dri2_surf->swap_queue_processor) {
+      pthread_mutex_lock(&dri2_surf->mutex);
+
+      /* Wait for any outstanding swaps to complete */
+      while (dri2_surf->swap_queue_idx_head != dri2_surf->swap_queue_idx_tail)
+         pthread_cond_wait(&dri2_surf->swap_unlock_buffer_cond,
+                           &dri2_surf->mutex);
+
+      pthread_mutex_unlock(&dri2_surf->mutex);
+      pthread_cancel(dri2_surf->swap_queue_processor);
+      pthread_join(dri2_surf->swap_queue_processor, NULL);
+   }
+
+   if (dri2_surf->cond_init)
+      pthread_cond_destroy(&dri2_surf->swap_queue_cond);
+
+   if (dri2_surf->cond_init_unlock_buffer)
+      pthread_cond_destroy(&dri2_surf->swap_unlock_buffer_cond);
+
+   if (dri2_surf->mutex_init)
+      pthread_mutex_destroy(&dri2_surf->mutex);
 
    if (dri2_surf->front)
       dri2_dpy->image->destroyImage(dri2_surf->front);
@@ -837,9 +1223,7 @@ dri2_null_swap_buffers(_EGLDisplay *disp, _EGLSurface *draw)
 {
    struct dri2_egl_display *dri2_dpy = dri2_egl_display(disp);
    struct dri2_egl_surface *dri2_surf = dri2_egl_surface(draw);
-   bool *plocked = NULL;
-   uint32_t flags;
-   int err;
+   uint32_t back_id;
 
    if (dri2_surf->base.Type != EGL_WINDOW_BIT)
       return EGL_TRUE;
@@ -858,34 +1242,13 @@ dri2_null_swap_buffers(_EGLDisplay *disp, _EGLSurface *draw)
    dri2_flush_drawable_for_swapbuffers(disp, draw);
    dri2_dpy->flush->invalidate(dri2_surf->dri_drawable);
 
-   if (dri2_surf->current) {
-      /* Wait for the previous flip to happen so the next one can be queued */
-      if (!flip_process(dri2_dpy->fd)) {
-         _eglError(EGL_BAD_NATIVE_WINDOW, "dri2_null_swap_buffers process");
-         return EGL_FALSE;
-      }
+   back_id = get_back_buffer_id(dri2_surf);
+   assert(dri2_surf->back == &dri2_surf->color_buffers[back_id]);
 
-      plocked = &dri2_surf->current->locked;
-   }
-
-   flags = DRM_MODE_PAGE_FLIP_EVENT;
-   if (draw->SwapInterval == 0)
-      flags |= DRM_MODE_PAGE_FLIP_ASYNC;
-
-   do {
-      err = display_output_flip(dri2_dpy->fd, &dri2_dpy->output,
-                                dri2_surf->back->fb_id, flags, plocked);
-   } while (err == -EBUSY);
-
-   if (err) {
-      _eglError(EGL_BAD_NATIVE_WINDOW, "dri2_null_swap_buffers flip");
-      dri2_surf->back->locked = false;
-      dri2_surf->back = NULL;
-      return EGL_FALSE;
-   }
+   swap_enqueue_data(dri2_surf, back_id, draw->SwapInterval);
 
+   /* This back buffer is tracked in the swap_data, safe to drop it now */
    dri2_surf->back->age = 1;
-   dri2_surf->current = dri2_surf->back;
    dri2_surf->back = NULL;
 
    return EGL_TRUE;
@@ -904,11 +1267,20 @@ dri2_null_query_buffer_age(_EGLDisplay *disp, _EGLSurface *surface)
    return dri2_surf->back->age;
 }
 
+static EGLBoolean
+dri2_null_swap_interval(_EGLDisplay *dpy, _EGLSurface *draw, EGLint interval)
+{
+   _eglLog(_EGL_DEBUG, "DRI2: set swap interval to %d", interval);
+   draw->SwapInterval = interval;
+   return EGL_TRUE;
+}
+
 static struct dri2_egl_display_vtbl dri2_null_display_vtbl = {
    .create_window_surface = dri2_null_create_window_surface,
    .create_pbuffer_surface = dri2_null_create_pbuffer_surface,
    .destroy_surface = dri2_null_destroy_surface,
    .create_image = dri2_create_image_khr,
+   .swap_interval = dri2_null_swap_interval,
    .swap_buffers = dri2_null_swap_buffers,
    .query_buffer_age = dri2_null_query_buffer_age,
    .get_dri_drawable = dri2_surface_get_dri_drawable,
@@ -1062,12 +1434,35 @@ dri2_null_add_configs_for_formats(_EGLDisplay *disp)
 
    return count != 0;
 }
+static void
+dri2_null_setup_swap_interval(_EGLDisplay *disp)
+{
+   struct dri2_egl_display *dri2_dpy = dri2_egl_display(disp);
+   const int swap_max_interval = 10; /* Arbitrary max value */
+   uint64_t value;
+   int err;
+
+   dri2_setup_swap_interval(disp, swap_max_interval);
+
+   err = drmGetCap(dri2_dpy->fd, DRM_CAP_ASYNC_PAGE_FLIP, &value);
+   if (err || value == 0)
+      dri2_dpy->min_swap_interval = 1;
+
+   /**
+    * drm/atomic: Reject FLIP_ASYNC unconditionally
+    * upstream f2cbda2dba11de868759cae9c0d2bab5b8411406
+    *
+    * Only allow swap interval 0 for legacy DRM/KMS and let
+    * the app be aware that swap interval is clamped to 1.
+    */
+   if (dri2_dpy->atomic_enabled)
+      dri2_dpy->min_swap_interval = 1;
+}
 
 EGLBoolean
 dri2_initialize_null(_EGLDisplay *disp)
 {
    struct dri2_egl_display *dri2_dpy;
-   uint64_t value;
    int err;
 
    dri2_dpy = calloc(1, sizeof(*dri2_dpy));
@@ -1114,11 +1509,7 @@ dri2_initialize_null(_EGLDisplay *disp)
    }
 
    dri2_setup_screen(disp);
-   dri2_setup_swap_interval(disp, 1);
-
-   err = drmGetCap(dri2_dpy->fd, DRM_CAP_ASYNC_PAGE_FLIP, &value);
-   if (err || value == 0)
-      dri2_dpy->min_swap_interval = 1;
+   dri2_null_setup_swap_interval(disp);
 
    if (dri2_dpy->image->base.version < NULL_IMAGE_EXTENSION_VERSION_MIN) {
       _eglError(EGL_NOT_INITIALIZED, "image extension version too old");