From 5212f22050e6e92812b14b6cd1fe5029ceeb4225 Mon Sep 17 00:00:00 2001
From: Luigi Santivetti <luigi.santivetti@imgtec.com>
Date: Mon, 21 Oct 2019 09:21:52 +0100
Subject: [PATCH] egl/null: add support for async flip with front buffer
 rendering

This change enables the application to render into the buffer being
scanned out if the display driver doesn't support
DRM_CAP_ASYNC_PAGE_FLIP.

The egl display now tracks the DRM async flip capabilities, allowing
platform_null to always return the buffer on screen to the application
when the swap interval is set to 0, but the DRM driver doesn't support
async flip.

platform_null can be in several alternative states by the time
eglSwapInterval() is called, following is a summary of them.

  1. platform_null was initialised and it has already flipped. In this
  case, return to the client API a reference to the buffer on screen

  2. platform_null was initialised but no back buffer was requested yet
  from the client API. In this case, return a reference to the front
  buffer

  3. platform_null was initialised and the client API has already got
  a back buffer, but no flip was scheduled. In this case, make sure
  to flip and return the buffer on the screen

Note that this change also refactors the color buffers and front
buffer code. Platform null after this change has a dedicated struct
for storing front buffer DRI data and framebuffer id.

Also be noted that min_swap_interval is no longer clamped to 1 when
DRM_CAP_ASYNC_PAGE_FLIP isn't supported. This is because,
if min_swap_interval is automatically promoted to 1, Mesa EGL will de
facto prevent the application from requesting any swap interval less
than 1.

Change-Id: I3930cfcdb30bfb5358166911bcf84a78bdb4548d
Signed-off-by: Luigi Santivetti <luigi.santivetti@imgtec.com>

---
 src/egl/drivers/dri2/egl_dri2.h      |   8 +-
 src/egl/drivers/dri2/platform_null.c | 153 +++++++++++++++++++++------
 2 files changed, 129 insertions(+), 32 deletions(-)

diff --git a/src/egl/drivers/dri2/egl_dri2.h b/src/egl/drivers/dri2/egl_dri2.h
index 32ad720..27beae5 100644
--- a/src/egl/drivers/dri2/egl_dri2.h
+++ b/src/egl/drivers/dri2/egl_dri2.h
@@ -283,6 +283,7 @@ struct dri2_egl_display
 #ifdef HAVE_NULL_PLATFORM
    bool                      atomic_enabled;
    bool                      in_formats_enabled;
+   bool                      async_flip_enabled;
    struct display_output     output;
 #endif
 
@@ -439,8 +440,12 @@ struct dri2_egl_surface
 #endif
       bool                locked;
       int                 age;
+#ifdef HAVE_NULL_PLATFORM
+   } color_buffers[DRI2_SURFACE_NUM_COLOR_BUFFERS], *back, *current, front_buffer;
+#else
    } color_buffers[DRI2_SURFACE_NUM_COLOR_BUFFERS], *back, *current;
 #endif
+#endif
 
 #ifdef HAVE_ANDROID_PLATFORM
    struct ANativeWindow *window;
@@ -469,12 +474,13 @@ struct dri2_egl_surface
 #endif
 
 #ifdef HAVE_NULL_PLATFORM
-   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                    front_render_enabled;
+   bool                    front_render_init;
    bool                    cond_init_unlock_buffer;
 #endif
 
diff --git a/src/egl/drivers/dri2/platform_null.c b/src/egl/drivers/dri2/platform_null.c
index 2c79199..0ce7e60 100644
--- a/src/egl/drivers/dri2/platform_null.c
+++ b/src/egl/drivers/dri2/platform_null.c
@@ -602,6 +602,15 @@ swap_dequeue_data_finish(struct dri2_egl_surface *dri2_surf)
    pthread_mutex_unlock(&dri2_surf->mutex);
 }
 
+static void
+swap_drain_queue_data(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_unlock_buffer_cond, &dri2_surf->mutex);
+   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)
@@ -1146,15 +1155,15 @@ get_front_bo(struct dri2_egl_surface *dri2_surf)
    if (dri2_surf->base.Type == EGL_WINDOW_BIT)
       use |= __DRI_IMAGE_USE_SCANOUT;
 
-   dri2_surf->front = create_image(dri2_surf, use);
-   if (!dri2_surf->front)
+   dri2_surf->front_buffer.dri_image = create_image(dri2_surf, use);
+   if (!dri2_surf->front_buffer.dri_image)
       return false;
 
    if (dri2_surf->base.Type == EGL_WINDOW_BIT) {
-      if (!add_fb_for_dri_image(dri2_dpy, dri2_surf->front,
-                                &dri2_surf->front_fb_id)) {
-         dri2_dpy->image->destroyImage(dri2_surf->front);
-         dri2_surf->front = NULL;
+      if (!add_fb_for_dri_image(dri2_dpy, dri2_surf->front_buffer.dri_image,
+                                &dri2_surf->front_buffer.fb_id)) {
+         dri2_dpy->image->destroyImage(dri2_surf->front_buffer.dri_image);
+         dri2_surf->front_buffer.dri_image = NULL;
          return false;
       }
    }
@@ -1362,7 +1371,7 @@ dri2_null_create_window_surface(_EGLDisplay *disp, _EGLConfig *config,
    }
 
    err = display_output_modeset(dri2_dpy->fd, &dri2_dpy->output,
-                                dri2_surf->front_fb_id);
+                                dri2_surf->front_buffer.fb_id);
    if (err) {
       _eglError(EGL_BAD_NATIVE_WINDOW, "window set mode");
       goto err_destroy_surface;
@@ -1392,6 +1401,60 @@ dri2_null_create_pbuffer_surface(_EGLDisplay *disp, _EGLConfig *config,
    return create_surface(disp, config, EGL_PBUFFER_BIT, attrib_list);
 }
 
+static void
+dri2_null_init_front_buffer_render(_EGLSurface *draw)
+{
+   struct dri2_egl_surface *dri2_surf = dri2_egl_surface(draw);
+
+   dri2_surf->front_render_init = true;
+
+   /* Drain the queue. swap_buffer_unlock_cond signals for the last time
+    * when the last back buffer in the queue went on screen and it's being
+    * tracked as current by then.
+    */
+   swap_drain_queue_data(dri2_surf);
+
+   /* If previously flipped, take a reference to the current buffer */
+   if (dri2_surf->current) {
+      assert(dri2_surf->current->dri_image);
+      dri2_surf->back = dri2_surf->current;
+
+      for (unsigned i = 0; i < DRI2_SURFACE_NUM_COLOR_BUFFERS; i++)
+         dri2_surf->color_buffers[i].age = 0;
+
+      return;
+   }
+
+   /* If the application hasn't yet fetched a back buffer, then it's not too
+    * late to use front buffer's dri_image and fb_id.
+    */
+   if (!dri2_surf->back) {
+      assert(dri2_surf->front_buffer.dri_image);
+      dri2_surf->back = &dri2_surf->front_buffer;
+
+      /* Don't need to reset buffer age since no flip was requested yet */
+
+      return;
+   }
+
+   /* In order to initialise one color buffer for front buffer rendering,
+    * one page flip must occur.
+    */
+   swap_enqueue_data(dri2_surf, get_back_buffer_id(dri2_surf), 1);
+
+   return dri2_null_init_front_buffer_render(draw);
+}
+
+static void
+dri2_null_disable_front_buffer_render(_EGLSurface *draw)
+{
+   struct dri2_egl_surface *dri2_surf = dri2_egl_surface(draw);
+
+   dri2_surf->front_render_enabled = false;
+   dri2_surf->front_render_init = false;
+   dri2_surf->back = NULL;
+}
+
 static EGLBoolean
 dri2_null_destroy_surface(_EGLDisplay *disp, _EGLSurface *surf)
 {
@@ -1403,14 +1466,7 @@ dri2_null_destroy_surface(_EGLDisplay *disp, _EGLSurface *surf)
     * sure we process the flip event.
     */
    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);
+      swap_drain_queue_data(dri2_surf);
       pthread_cancel(dri2_surf->swap_queue_processor);
       pthread_join(dri2_surf->swap_queue_processor, NULL);
    }
@@ -1424,11 +1480,11 @@ dri2_null_destroy_surface(_EGLDisplay *disp, _EGLSurface *surf)
    if (dri2_surf->mutex_init)
       pthread_mutex_destroy(&dri2_surf->mutex);
 
-   if (dri2_surf->front)
-      dri2_dpy->image->destroyImage(dri2_surf->front);
+   if (dri2_surf->front_buffer.dri_image)
+      dri2_dpy->image->destroyImage(dri2_surf->front_buffer.dri_image);
 
-   if (dri2_surf->front_fb_id)
-         drmModeRmFB(dri2_dpy->fd, dri2_surf->front_fb_id);
+   if (dri2_surf->front_buffer.fb_id)
+         drmModeRmFB(dri2_dpy->fd, dri2_surf->front_buffer.fb_id);
 
    for (unsigned i = 0; i < ARRAY_SIZE(dri2_surf->color_buffers); i++) {
       if (dri2_surf->color_buffers[i].fb_id)
@@ -1455,6 +1511,16 @@ dri2_null_swap_buffers(_EGLDisplay *disp, _EGLSurface *draw)
    if (dri2_surf->base.Type != EGL_WINDOW_BIT)
       return EGL_TRUE;
 
+   /* Flush and early return, no swap takes place */
+   if (dri2_surf->front_render_enabled) {
+      dri2_flush_drawable_for_swapbuffers(disp, draw);
+
+      if (!dri2_surf->front_render_init)
+         dri2_null_init_front_buffer_render(draw);
+
+      return EGL_TRUE;
+   }
+
    for (unsigned i = 0; i < ARRAY_SIZE(dri2_surf->color_buffers); i++)
       if (dri2_surf->color_buffers[i].age > 0)
          dri2_surf->color_buffers[i].age++;
@@ -1497,6 +1563,22 @@ dri2_null_query_buffer_age(_EGLDisplay *disp, _EGLSurface *surface)
 static EGLBoolean
 dri2_null_swap_interval(_EGLDisplay *dpy, _EGLSurface *draw, EGLint interval)
 {
+   struct dri2_egl_surface *dri2_surf = dri2_egl_surface(draw);
+   struct dri2_egl_display *dri2_dpy =
+      dri2_egl_display(dri2_surf->base.Resource.Display);
+
+   /* dri2_dpy tracks whether the display driver is async flip capable.
+    * If it isn't, enable front buffer rendering when swap interval
+    * 0 is passed in from the application.
+    */
+   if (!interval && !dri2_dpy->async_flip_enabled) {
+      if (!dri2_surf->front_render_enabled)
+         dri2_surf->front_render_enabled = true;
+   } else {
+      if (dri2_surf->front_render_enabled)
+         dri2_null_disable_front_buffer_render(draw);
+   }
+
    _eglLog(_EGL_DEBUG, "DRI2: set swap interval to %d", interval);
    draw->SwapInterval = interval;
    return EGL_TRUE;
@@ -1534,7 +1616,7 @@ dri2_null_image_get_buffers(__DRIdrawable *driDrawable, unsigned int format,
 
    if (buffer_mask & __DRI_IMAGE_BUFFER_FRONT) {
       buffers->image_mask |= __DRI_IMAGE_BUFFER_FRONT;
-      buffers->front = dri2_surf->front;
+      buffers->front = dri2_surf->front_buffer.dri_image;
    }
 
    if (buffer_mask & __DRI_IMAGE_BUFFER_BACK) {
@@ -1672,18 +1754,27 @@ dri2_null_setup_swap_interval(_EGLDisplay *disp)
    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;
+   if (err || value == 0) {
 
-   /**
-    * 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;
+      /* DRM/KMS does not support async page flip. In order to support
+       * swap interval 0, use front buffer rendering.
+       */
+      _eglLog(_EGL_DEBUG,
+              "drm async flip not supported, use front buffer");
+   } else {
+
+      /* drm/atomic: Reject FLIP_ASYNC unconditionally
+       * upstream f2cbda2dba11de868759cae9c0d2bab5b8411406
+       *
+       * Legacy DRM/KMS can use DRM_MODE_PAGE_FLIP_ASYNC, for atomic
+       * drivers fallback to front buffer rendering.
+       */
+      if (dri2_dpy->atomic_enabled)
+         _eglLog(_EGL_DEBUG,
+                 "async flip not supported by atomic, use front buffer");
+      else
+         dri2_dpy->async_flip_enabled = true;
+   }
 }
 
 EGLBoolean
