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[KMS/DRM] Refactor, improve and re-comment async pageflips code.
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parent
fbd7c718b6
commit
ead3c406a2
src/video/kmsdrm
@ -154,13 +154,14 @@ KMSDRM_GLES_SwapWindow(_THIS, SDL_Window * window) {
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/* Issue pageflip on the next front buffer.
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Remember: drmModePageFlip() never blocks, it just issues the flip,
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which will be done during the next vblank.
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Since it will return EBUSY if we call it again without having
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completed the last issued flip, we must pass the
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which will be done during the next vblank, or immediately if
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we pass the DRM_MODE_PAGE_FLIP_ASYNC flag.
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Since calling drmModePageFlip() will return EBUSY if we call it
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without having completed the last issued flip, we must pass the
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DRM_MODE_PAGE_FLIP_ASYNC if we don't block on EGL (egl_swapinterval = 0).
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That makes it flip immediately, without waiting for the next vblank,
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so even if we don't block on EGL, it will have flipped when we
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get back here. */
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That makes it flip immediately, without waiting for the next vblank
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to do so, so even if we don't block on EGL, the flip will have completed
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when we get here again. */
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if (_this->egl_data->egl_swapinterval == 0) {
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flip_flags |= DRM_MODE_PAGE_FLIP_ASYNC;
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@ -173,11 +174,15 @@ KMSDRM_GLES_SwapWindow(_THIS, SDL_Window * window) {
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windata->waiting_for_flip = SDL_TRUE;
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} else {
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SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "Could not queue pageflip: %d", ret);
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printf("Could not queue pageflip: %s\n", strerror(errno));
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}
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/* If we are in double-buffer mode, wait immediately for vsync
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(as if we only had two buffers),
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/* Wait immediately for vsync (as if we only had two buffers).
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Even if we are already doing a WaitPageFlip at the begining of this
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function, this is NOT redundant because here we wait immediately
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after submitting the image to the screen, reducing lag, and if
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we have waited here, there won't be a pending pageflip so the
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WaitPageFlip at the beggining of this function will be a no-op.
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Just leave it here and don't worry.
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Run your SDL2 program with "SDL_KMSDRM_DOUBLE_BUFFER=1 <program_name>"
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to enable this. */
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if (_this->egl_data->egl_swapinterval == 1 && windata->double_buffer) {
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@ -45,8 +45,9 @@
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#include "SDL_kmsdrmvulkan.h"
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#include <sys/stat.h>
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#include <dirent.h>
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#include <errno.h>
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#include <poll.h>
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#include <time.h>
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#include <errno.h>
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#ifdef __OpenBSD__
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#define KMSDRM_DRI_PATH "/dev/"
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@ -340,42 +341,63 @@ KMSDRM_FlipHandler(int fd, unsigned int frame, unsigned int sec, unsigned int us
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SDL_bool
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KMSDRM_WaitPageFlip(_THIS, SDL_WindowData *windata) {
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SDL_VideoData *viddata = ((SDL_VideoData *)_this->driverdata);
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drmEventContext ev = {0};
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struct pollfd pfd = {0};
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/* If the pageflip hasn't completed after 10 seconds, it nevel will. */
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uint32_t timeout = 10000;
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ev.version = DRM_EVENT_CONTEXT_VERSION;
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ev.page_flip_handler = KMSDRM_FlipHandler;
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pfd.fd = viddata->drm_fd;
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pfd.events = POLLIN;
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/* Stay on loop until we get the desired event
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We need the while the loop because we could be in a situation where:
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-We get events on the FD in time, thus not on exiting on return number 1.
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-These events are not errors, thus not exiting on return number 2.
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-These events are of POLLIN type, thus not exiting on return number 3,
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but if the event is not the pageflip we are waiting for, we arrive at the end
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of the loop and do loop re-entry, hoping the next event will be the pageflip.
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So we could erroneously exit the function without the pageflip event to arrive
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if it wasn't for the while loop!
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Vblank events, for example, hit the FD and they are POLLIN events too (POLLIN
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means "there's data to read on the FD"), but they are not the pageflip event
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we are waiting for, so the drmEventHandle() doesn't run the flip handler, and
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since waiting_for_flip is set on the pageflip handle, it's not set and we stay
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on the loop.
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*/
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while (windata->waiting_for_flip) {
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pfd.revents = 0;
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pfd.revents = 0;
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/* poll() waits for events arriving on the FD, and returns < 0 if timeout
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passes with no events. */
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if (poll(&pfd, 1, timeout) < 0) {
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passes with no events.
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We wait forever (timeout = -1), but even if we DO get an event,
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we have yet to see if it's of the required type. */
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if (poll(&pfd, 1, -1) < 0) {
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SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "DRM poll error");
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return SDL_FALSE;
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return SDL_FALSE; /* Return number 1. */
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}
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if (pfd.revents & (POLLHUP | POLLERR)) {
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/* An event arrived on the FD in time, but it's an error. */
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SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "DRM poll hup or error");
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return SDL_FALSE;
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return SDL_FALSE; /* Return number 2. */
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}
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if (pfd.revents & POLLIN) {
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/* There is data to read on the FD!
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Is the event a pageflip? If so, drmHandleEvent will
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unset windata->waiting_for_flip */
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Is the event a pageflip? We know it is a pageflip if it matches the
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event we are passing in &ev. If it is, drmHandleEvent() will unset
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windata->waiting_for_flip and we will get out of the "while" loop.
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If it's not, we keep iterating on the loop. */
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KMSDRM_drmHandleEvent(viddata->drm_fd, &ev);
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} else {
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SDL_LogDebug(SDL_LOG_CATEGORY_VIDEO, "Dropping frame while waiting_for_flip");
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return SDL_FALSE;
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return SDL_FALSE; /* Return number 3. */
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}
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}
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