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kmsdrm: double and triple buffered versions of SwapWindow() are now b…
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…oth reimplemented in atomic pageflipping versions, and can be selected via SDL_VIDEO_DOUBLE_BUFFER env variable.
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@vanfanel
vanfanel committed Aug 5, 2020
1 parent 8996ee1 commit 2d69ce0
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Showing 4 changed files with 99 additions and 173 deletions.
244 changes: 86 additions & 158 deletions src/video/kmsdrm/SDL_kmsdrmopengles.c
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Expand Up @@ -73,123 +73,51 @@ static EGLSyncKHR create_fence(int fd, _THIS)
return fence;
}

/*
-We have to stop the GPU from executing the cmdstream again because the front butter
has been marked as back buffer so it can be selected by EGL to draw on it BUT
the pageflip has not completed, so it's still on screen, so letting GPU render on it
would cause tearing. (kms_fence)
-We have to stop the DISPLAY from doing the changes we requested in the atomic ioctl,
like the pageflip, until the GPU has completed the cmdstream execution,
because we don't want the pageflip to be done in the middle of a frame rendering.
(gpu_fence).
-We have to stop the program from doing a new atomic ioctl until the previous one
has been finished. (kms_fence)
*/

int
KMSDRM_GLES_SwapWindowDOUBLE(_THIS, SDL_Window * window) {

KMSDRM_GLES_SwapWindow(_THIS, SDL_Window * window)
{
SDL_WindowData *windata = ((SDL_WindowData *) window->driverdata);
SDL_DisplayData *dispdata = (SDL_DisplayData *) SDL_GetDisplayForWindow(window)->driverdata;
KMSDRM_FBInfo *fb;

EGLint status;
int ret;

uint32_t flags = DRM_MODE_ATOMIC_NONBLOCK;

EGLSyncKHR kms_in_fence = NULL;
EGLSyncKHR kms_out_fence = NULL;

/* Create the display in-fence, and export it as a fence fd to pass into the kernel. */
kms_in_fence = create_fence(EGL_NO_NATIVE_FENCE_FD_ANDROID, _this);
assert(kms_in_fence);
dispdata->kms_in_fence_fd = _this->egl_data->eglDupNativeFenceFDANDROID(_this->egl_data->egl_display, kms_in_fence);

/* Mark the back buffer as the next front buffer, and the current front buffer as elegible
by EGL as back buffer to draw into.
This will not really happen until we post the pageflip though KMS with the atomic ioctl
and it completes on next vsync. */
_this->egl_data->eglSwapBuffers(_this->egl_data->egl_display, windata->egl_surface);

/* Lock the buffer that is marked by eglSwapBuffers() to become the next front buffer (so it can not
be chosen by EGL as back buffer to draw on), and get a handle to it, so we can use that handle
to request the KMS pageflip that will set it as front buffer. */
windata->next_bo = KMSDRM_gbm_surface_lock_front_buffer(windata->gs);
if (!windata->next_bo) {
printf("Failed to lock frontbuffer\n");
return -1;
}
fb = KMSDRM_FBFromBO(_this, windata->next_bo);
if (!fb) {
printf("Failed to get a new framebuffer BO\n");
return -1;
}

/*
* Issue atomic pageflip to post the pageflip thru KMS. Returns immediately.
* Never issue an atomic ioctl while the previuos one is pending: it will be rejected.
*/
ret = drm_atomic_commit(_this, fb->fb_id, flags);
if (ret) {
printf("failed to do atomic commit\n");
return -1;
}
uint32_t flags = DRM_MODE_ATOMIC_NONBLOCK;

/* Get the display out fence, returned by the atomic ioctl. */
kms_out_fence = create_fence(dispdata->kms_out_fence_fd, _this);
assert(kms_out_fence);

/* Wait on the CPU side for the _previous_ commit to complete before we post the flip through KMS,
* because atomic will reject the commit if we post a new one while the previous one is still pending. */
do {
status = _this->egl_data->eglClientWaitSyncKHR(_this->egl_data->egl_display, kms_out_fence, 0, EGL_FOREVER_KHR);
} while (status != EGL_CONDITION_SATISFIED_KHR);

/* Destroy both in and out display fences. */
_this->egl_data->eglDestroySyncKHR(_this->egl_data->egl_display, kms_out_fence);
_this->egl_data->eglDestroySyncKHR(_this->egl_data->egl_display, kms_in_fence);

/* Now that the pageflip is complete, release last front buffer so EGL can chose it
* as back buffer and render on it again: */
if (windata->curr_bo) {
KMSDRM_gbm_surface_release_buffer(windata->gs, windata->curr_bo);
windata->curr_bo = NULL;
/* Do we need to set video mode this time? */
if (windata->crtc_setup_pending) {
flags |= DRM_MODE_ATOMIC_ALLOW_MODESET;
windata->crtc_setup_pending = SDL_FALSE;
}

/* Take note of the current front buffer, so it can be freed next time this function is called. */
windata->curr_bo = windata->next_bo;

return ret;
}


int
KMSDRM_GLES_SwapWindow(_THIS, SDL_Window * window) {

SDL_WindowData *windata = ((SDL_WindowData *) window->driverdata);
SDL_DisplayData *dispdata = (SDL_DisplayData *) SDL_GetDisplayForWindow(window)->driverdata;
KMSDRM_FBInfo *fb;
int ret;

uint32_t flags = DRM_MODE_ATOMIC_NONBLOCK;
/*************************************************************************/
/* Block for telling KMS to wait for GPU rendering of the current frame */
/* before applying the KMS changes requested in the atomic ioctl. */
/*************************************************************************/

/* Create the fence that will be inserted in the cmdstream exactly at the end
of the gl commands that form a frame. KMS will have to wait on it before doing a pageflip. */
dispdata->gpu_fence = create_fence(EGL_NO_NATIVE_FENCE_FD_ANDROID, _this);
assert(dispdata->gpu_fence);

/* Mark in the EGL level the buffer that we want to become the new front buffer.
However, it won't really happen until we request a pageflip at the KMS level and it completes. */
_this->egl_data->eglSwapBuffers(_this->egl_data->egl_display, windata->egl_surface);

/* It's safe to get the gpu_fence FD now, because eglSwapBuffers flushes it
down the cmdstream, so it's now in place in the cmdstream.
Atomic ioctl will pass the in-fence fd into the kernel. */
/* It's safe to get the gpu_fence FD now, because eglSwapBuffers flushes it down the cmdstream,
so it's now in place in the cmdstream.
Atomic ioctl will pass the in-fence fd into the kernel, telling KMS that it has to wait for GPU to
finish rendering the frame before doing the changes requested in the atomic ioct (pageflip in this case). */
dispdata->kms_in_fence_fd = _this->egl_data->eglDupNativeFenceFDANDROID(_this->egl_data->egl_display, dispdata->gpu_fence);
_this->egl_data->eglDestroySyncKHR(_this->egl_data->egl_display, dispdata->gpu_fence);
assert(dispdata->kms_in_fence_fd != -1);

/***************/
/* Block ends. */
/***************/

/* Lock the buffer that is marked by eglSwapBuffers() to become the next front buffer (so it can not
be chosen by EGL as back buffer to draw on), and get a handle to it to request the pageflip on it. */
be chosen by EGL as back buffer to draw on), and get a handle to it to request the pageflip on it. */
windata->next_bo = KMSDRM_gbm_surface_lock_front_buffer(windata->gs);
if (!windata->next_bo) {
printf("Failed to lock frontbuffer\n");
Expand All @@ -201,8 +129,7 @@ KMSDRM_GLES_SwapWindow(_THIS, SDL_Window * window) {
return -1;
}


/* Don't issue another atomic ioctl until previous one has completed. */
/* Don't issue another atomic ioctl until previous one has completed: it will cause errors. */
if (dispdata->kms_fence) {
EGLint status;

Expand All @@ -213,81 +140,81 @@ KMSDRM_GLES_SwapWindow(_THIS, SDL_Window * window) {
_this->egl_data->eglDestroySyncKHR(_this->egl_data->egl_display, dispdata->kms_fence);
}


/* Issue atomic commit. */
/* Issue atomic commit, where we request the pageflip. */
ret = drm_atomic_commit(_this, fb->fb_id, flags);
if (ret) {
printf("failed to do atomic commit\n");
return -1;
}



/* release last front buffer so EGL can chose it as back buffer and render on it again: */
if (windata->curr_bo) {
KMSDRM_gbm_surface_release_buffer(windata->gs, windata->curr_bo);
windata->curr_bo = NULL;
/* Release the last front buffer so EGL can chose it as back buffer and render on it again. */
if (windata->bo) {
KMSDRM_gbm_surface_release_buffer(windata->gs, windata->bo);
}

/* Take note of the current front buffer, so it can be freed next time this function is called. */
windata->curr_bo = windata->next_bo;
/* Take note of current front buffer, so we can free it next time we come here. */
windata->bo = windata->next_bo;

/**************************************************************************/
/* Block for telling GPU to wait for completion of requested KMS changes */
/* before starting cmdstream execution (=next frame rendering). */
/**************************************************************************/

/* Import out fence from the out fence fd and tell the GPU to wait on it
until the requested pageflip has completed. */
/* Import the kms fence from the out fence fd. We need it to tell GPU to wait for pageflip to complete. */
dispdata->kms_fence = create_fence(dispdata->kms_out_fence_fd, _this);
assert(dispdata->kms_fence);

/* Reset out fence FD value because the fence is now away from us, on the driver side. */
dispdata->kms_out_fence_fd = -1;

/* Tell the GPU to wait until the requested pageflip has completed. */
_this->egl_data->eglWaitSyncKHR(_this->egl_data->egl_display, dispdata->kms_fence, 0);

return ret;
/***************/
/* Block ends. */
/***************/

return ret;
}

int
KMSDRM_GLES_SwapWindowOLD(_THIS, SDL_Window * window) {

KMSDRM_GLES_SwapWindowDB(_THIS, SDL_Window * window)
{
SDL_WindowData *windata = ((SDL_WindowData *) window->driverdata);
SDL_DisplayData *dispdata = (SDL_DisplayData *) SDL_GetDisplayForWindow(window)->driverdata;
KMSDRM_FBInfo *fb;
int ret;

/* Do we need to set video mode this time? */
uint32_t flags = DRM_MODE_ATOMIC_NONBLOCK;
if (windata->crtc_setup_pending) {
flags |= DRM_MODE_ATOMIC_ALLOW_MODESET;
windata->crtc_setup_pending = SDL_FALSE;
}

dispdata->kms_fence = NULL; /* in-fence to gpu, out-fence from kms */
dispdata->gpu_fence = NULL; /* in-fence to kms, out-fence from gpu, */

/* Allow modeset (which is done inside atomic_commit). */
flags |= DRM_MODE_ATOMIC_ALLOW_MODESET;


/* Import out fence from the out fence fd and tell the GPU to wait on it
until the requested pageflip has completed. */
dispdata->kms_fence = create_fence(dispdata->kms_out_fence_fd, _this);
assert(dispdata->kms_fence);

dispdata->kms_out_fence_fd = -1;


_this->egl_data->eglWaitSyncKHR(_this->egl_data->egl_display, dispdata->kms_fence, 0);


/* GL DRAW */

/* Create the gpu fence here so it's inserted in the cmdstream exactly
at the end of the gl commands that form a frame. */
/* Create the fence that will be inserted in the cmdstream exactly at the end
of the gl commands that form a frame. KMS will have to wait on it before doing a pageflip.
(NOTE this fence is not really neeeded in double-buffer mode because the program will be
blocked in eglClientWaitSyncKMHR() until pageflip completes, but we need an in-fence FD anyway
to issue the atomic ioctl).
*/
dispdata->gpu_fence = create_fence(EGL_NO_NATIVE_FENCE_FD_ANDROID, _this);
assert(dispdata->gpu_fence);

_this->egl_data->eglSwapBuffers(_this->egl_data->egl_display, windata->egl_surface);

/* It's safe to get the gpu_fence fd now, because eglSwapBuffers() flushes the fd. */
/* It's safe to get the gpu_fence FD now, because eglSwapBuffers flushes it down the cmdstream,
so it's now in place in the cmdstream.
Atomic ioctl will pass the in-fence fd into the kernel, telling KMS that it has to wait for GPU to
finish rendering the frame before doing the changes requested in the atomic ioct (pageflip in this case). */
dispdata->kms_in_fence_fd = _this->egl_data->eglDupNativeFenceFDANDROID(_this->egl_data->egl_display, dispdata->gpu_fence);

_this->egl_data->eglDestroySyncKHR(_this->egl_data->egl_display, dispdata->gpu_fence);
assert(dispdata->kms_in_fence_fd != -1);

/* Mark in the EGL level the buffer that we want to become the new front buffer.
However, it won't really happen until we request a pageflip at the KMS level and it completes. */
_this->egl_data->eglSwapBuffers(_this->egl_data->egl_display, windata->egl_surface);

/* Lock the buffer that is marked by eglSwapBuffers() to become the next front buffer (so it can not
be chosen by EGL as back buffer to draw on), and get a handle to it to request the pageflip on it. */
windata->next_bo = KMSDRM_gbm_surface_lock_front_buffer(windata->gs);
if (!windata->next_bo) {
printf("Failed to lock frontbuffer\n");
Expand All @@ -299,42 +226,43 @@ KMSDRM_GLES_SwapWindowOLD(_THIS, SDL_Window * window) {
return -1;
}

if (dispdata->kms_fence) {
EGLint status;

do {
status = _this->egl_data->eglClientWaitSyncKHR(_this->egl_data->egl_display, dispdata->kms_fence, 0, EGL_FOREVER_KHR);
} while (status != EGL_CONDITION_SATISFIED_KHR);

_this->egl_data->eglDestroySyncKHR(_this->egl_data->egl_display, dispdata->kms_fence);
}


/* Issue atomic commit. */
/* Issue atomic commit, where we request the pageflip. */
ret = drm_atomic_commit(_this, fb->fb_id, flags);
if (ret) {
printf("failed to do atomic commit\n");
return -1;
}

/* Release last front buffer so EGL can chose it as back buffer and render on it again. */
if (windata->bo) {
KMSDRM_gbm_surface_release_buffer(windata->gs, windata->bo);
}

/* Take note of current front buffer, so we can free it next time we come here. */
windata->bo = windata->next_bo;

/* release last front buffer so EGL can chose it as back buffer and render on it again: */
if (windata->curr_bo) {
KMSDRM_gbm_surface_release_buffer(windata->gs, windata->curr_bo);
windata->curr_bo = NULL;
}
/* Import the kms fence from the out fence fd. We need it to tell GPU to wait for pageflip to complete. */
dispdata->kms_fence = create_fence(dispdata->kms_out_fence_fd, _this);
assert(dispdata->kms_fence);

/* Take note of the current front buffer, so it can be freed next time this function is called. */
windata->curr_bo = windata->next_bo;
/* Reset out fence FD value because the fence is now away from us, on the driver side. */
dispdata->kms_out_fence_fd = -1;

/* Allow a modeset change for the first commit only. */
flags &= ~(DRM_MODE_ATOMIC_ALLOW_MODESET);
/* Wait for pageflip to complete, and destroy kms_fence. */
if (dispdata->kms_fence) {
EGLint status;

do {
status = _this->egl_data->eglClientWaitSyncKHR(_this->egl_data->egl_display, dispdata->kms_fence, 0, EGL_FOREVER_KHR);
} while (status != EGL_CONDITION_SATISFIED_KHR);

_this->egl_data->eglDestroySyncKHR(_this->egl_data->egl_display, dispdata->kms_fence);
}

return ret;
}


/***************************************/
/* End of Atomic functions block */
/***************************************/
Expand Down
1 change: 1 addition & 0 deletions src/video/kmsdrm/SDL_kmsdrmopengles.h
View file
Expand Up @@ -39,6 +39,7 @@ extern int KMSDRM_GLES_SetSwapInterval(_THIS, int interval);
extern int KMSDRM_GLES_LoadLibrary(_THIS, const char *path);
extern SDL_GLContext KMSDRM_GLES_CreateContext(_THIS, SDL_Window * window);
extern int KMSDRM_GLES_SwapWindow(_THIS, SDL_Window * window);
extern int KMSDRM_GLES_SwapWindowDB(_THIS, SDL_Window * window);
extern int KMSDRM_GLES_MakeCurrent(_THIS, SDL_Window * window, SDL_GLContext context);

#endif /* SDL_VIDEO_DRIVER_KMSDRM && SDL_VIDEO_OPENGL_EGL */
Expand Down

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