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Remove async and non-blocking page flip support

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It doesn't work well in practice for a few major reasons:
- It can result in the decoder writing on DMA-BUFs being used by the display
- It can generate page flip events that collide with Qt/SDL
- It can stall the decoder if the DMA-BUF has a fence on it from the display driver
This commit is contained in:
Cameron Gutman
2026-01-03 00:29:24 -06:00
parent c0846155c3
commit 2972022ced
2 changed files with 45 additions and 180 deletions
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3
app/streaming/video/ffmpeg-renderers/drm.cpp
View File

@@ -164,7 +164,6 @@ DrmRenderer::~DrmRenderer()
m_PropSetter.disablePlane(m_OverlayPlanes[i]);
}
m_PropSetter.apply();
m_PropSetter.waitForFlipCompletion();
}
for (int i = 0; i < k_SwFrameCount; i++) {
@@ -495,7 +494,7 @@ bool DrmRenderer::initialize(PDECODER_PARAMETERS params)
atomic = true;
}
m_PropSetter.initialize(m_DrmFd, atomic, !params->enableVsync);
m_PropSetter.initialize(m_DrmFd, atomic);
drmModePlaneRes* planeRes = drmModeGetPlaneResources(m_DrmFd);
if (planeRes == nullptr) {

222
app/streaming/video/ffmpeg-renderers/drm.h
View File

@@ -10,17 +10,10 @@
#include <xf86drm.h>
#include <xf86drmMode.h>
#include <poll.h>
#include <set>
#include <unordered_map>
#include <mutex>
// This is only defined in Linux 6.8+ headers
#ifndef DRM_CAP_ATOMIC_ASYNC_PAGE_FLIP
#define DRM_CAP_ATOMIC_ASYNC_PAGE_FLIP 0x15
#endif
// Newer libdrm headers have these HDR structs, but some older ones don't.
namespace DrmDefs
{
@@ -202,9 +195,6 @@ class DrmRenderer : public IFFmpegRenderer {
uint32_t crtcId;
int32_t crtcX, crtcY;
uint32_t crtcW, crtcH, srcX, srcY, srcW, srcH;
bool isPrimaryPlane;
bool needsSetPlane;
};
struct PlaneBuffer {
@@ -218,12 +208,7 @@ class DrmRenderer : public IFFmpegRenderer {
};
public:
DrmPropertySetter() {
m_EventCtx = {};
m_EventCtx.version = 2;
m_EventCtx.page_flip_handler = pageFlipHandler;
}
DrmPropertySetter() {}
~DrmPropertySetter() {
for (auto it = m_PlaneBuffers.begin(); it != m_PlaneBuffers.end(); it++) {
SDL_assert(!it->second.fbId);
@@ -247,21 +232,9 @@ class DrmRenderer : public IFFmpegRenderer {
DrmPropertySetter(const DrmPropertySetter &) = delete;
DrmPropertySetter(DrmPropertySetter &&) = delete;
void initialize(int drmFd, bool wantsAtomic, bool wantsAsyncFlip) {
void initialize(int drmFd, bool wantsAtomic) {
m_Fd = drmFd;
m_Atomic = wantsAtomic && drmSetClientCap(drmFd, DRM_CLIENT_CAP_ATOMIC, 1) == 0;
m_AsyncFlip = wantsAsyncFlip;
if (wantsAsyncFlip) {
uint64_t val;
if (drmGetCap(m_Fd,
m_Atomic ? DRM_CAP_ATOMIC_ASYNC_PAGE_FLIP : DRM_CAP_ASYNC_PAGE_FLIP,
&val) < 0 || !val) {
SDL_LogWarn(SDL_LOG_CATEGORY_APPLICATION,
"V-sync cannot be disabled due to lack of async page flip support");
m_AsyncFlip = false;
}
}
}
bool set(const DrmProperty& prop, uint64_t value, bool verbose = true) {
@@ -338,71 +311,18 @@ class DrmRenderer : public IFFmpegRenderer {
else {
PlaneConfiguration planeConfig;
// Wait for any previous flips to complete
waitForFlipCompletion();
{
// Latch the plane configuration and release the lock
std::lock_guard lg { m_Lock };
planeConfig = m_PlaneConfigs.at(plane.objectId());
m_PlaneConfigs[plane.objectId()].needsSetPlane = false;
}
// If we're flipping onto the primary plane, we can use drmModePageFlip()
// which allows support for async flips for legacy drivers
if (planeConfig.isPrimaryPlane && fbId && !planeConfig.needsSetPlane) {
// We always want the flip event
uint32_t flags = DRM_MODE_PAGE_FLIP_EVENT;
ret = drmModePageFlip(m_Fd, planeConfig.crtcId, fbId,
flags | (m_AsyncFlip ? DRM_MODE_PAGE_FLIP_ASYNC : 0),
this) == 0;
if (!ret && m_AsyncFlip) {
// Async page flips may be unavailable, so try a regular page flip
ret = drmModePageFlip(m_Fd, planeConfig.crtcId, fbId,
flags, this) == 0;
}
if (ret) {
// We had a successful (async) flip, so we need to wait to free the
// old buffers until the flip has fully completed
std::lock_guard lg { m_Lock };
// Queue the buffers to be freed and importantly also zero them
// so the cleanup code at the bottom of this function doesn't
// try to free them too early.
if (m_PlaneBuffers[plane.objectId()].fbId) {
m_FbsToFreeAfterFlip.push_back(m_PlaneBuffers[plane.objectId()].fbId);
m_PlaneBuffers[plane.objectId()].fbId = 0;
}
if (m_PlaneBuffers[plane.objectId()].dumbBufferHandle) {
m_DumbBufsToFreeAfterFlip.push_back(m_PlaneBuffers[plane.objectId()].dumbBufferHandle);
m_PlaneBuffers[plane.objectId()].dumbBufferHandle = 0;
}
// Expect a page flip event
SDL_assert(!m_FlipPending);
m_FlipPending = true;
}
else {
SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
"drmModePageFlip() failed: %d",
errno);
}
}
else {
ret = drmModeSetPlane(m_Fd, plane.objectId(),
planeConfig.crtcId, fbId, 0,
planeConfig.crtcX, planeConfig.crtcY,
planeConfig.crtcW, planeConfig.crtcH,
planeConfig.srcX, planeConfig.srcY,
planeConfig.srcW, planeConfig.srcH) == 0;
if (!ret) {
SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
"drmModeSetPlane() failed: %d",
errno);
}
}
ret = drmModeSetPlane(m_Fd, plane.objectId(),
planeConfig.crtcId, fbId, 0,
planeConfig.crtcX, planeConfig.crtcY,
planeConfig.crtcW, planeConfig.crtcH,
planeConfig.srcX, planeConfig.srcY,
planeConfig.srcW, planeConfig.srcH) == 0;
// If we succeeded updating the plane, free the old FB state
// Otherwise, we'll free the new data which was never used.
@@ -412,6 +332,11 @@ class DrmRenderer : public IFFmpegRenderer {
std::swap(fbId, m_PlaneBuffers[plane.objectId()].fbId);
std::swap(dumbBufferHandle, m_PlaneBuffers[plane.objectId()].dumbBufferHandle);
}
else {
SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
"drmModeSetPlane() failed: %d",
errno);
}
}
// Free the unused resources
@@ -458,9 +383,6 @@ class DrmRenderer : public IFFmpegRenderer {
planeConfig.srcY = srcY;
planeConfig.srcW = srcW;
planeConfig.srcH = srcH;
planeConfig.isPrimaryPlane = (plane.property("type")->initialValue() == DRM_PLANE_TYPE_PRIMARY);
planeConfig.needsSetPlane = true; // We must call drmModeSetPlane() once
}
return ret;
@@ -478,55 +400,56 @@ class DrmRenderer : public IFFmpegRenderer {
return 0;
}
// Wait for any previous flips to complete before acquiring the lock
waitForFlipCompletion();
drmModeAtomicReqPtr req = nullptr;
std::unordered_map<uint32_t, PlaneBuffer> pendingBuffers;
std::lock_guard lg { m_Lock };
{
// Take ownership of the current atomic request to commit it and
// allow other threads to queue up changes for the next one.
std::lock_guard lg { m_Lock };
std::swap(req, m_AtomicReq);
std::swap(pendingBuffers, m_PlaneBuffers);
}
if (!m_AtomicReq) {
if (!req) {
// Nothing to apply
return true;
}
// We always need these flags for completion notification
uint32_t flags = DRM_MODE_ATOMIC_NONBLOCK | DRM_MODE_PAGE_FLIP_EVENT;
// Try an async flip if requested
bool ret = drmModeAtomicCommit(m_Fd, m_AtomicReq,
flags | (m_AsyncFlip ? DRM_MODE_PAGE_FLIP_ASYNC : DRM_MODE_ATOMIC_ALLOW_MODESET),
this) == 0;
// The driver may not support async flips (especially if we changed a non-FB_ID property),
// so try again with a regular flip if we get an error from the async flip attempt.
//
// We pass DRM_MODE_ATOMIC_ALLOW_MODESET because changing HDR state may require a modeset.
if (!ret && m_AsyncFlip) {
ret = drmModeAtomicCommit(m_Fd, m_AtomicReq, flags | DRM_MODE_ATOMIC_ALLOW_MODESET, this) == 0;
}
// We pass DRM_MODE_ATOMIC_ALLOW_MODESET because changing HDR state may require a modeset
bool ret = drmModeAtomicCommit(m_Fd, req, DRM_MODE_ATOMIC_ALLOW_MODESET, nullptr) == 0;
// If we flipped to a new buffer, free the old one
if (ret) {
// Expect a page flip event
SDL_assert(!m_FlipPending);
m_FlipPending = true;
std::lock_guard lg { m_Lock };
// Update the buffer state for any modified planes
for (auto it = m_PlaneBuffers.begin(); it != m_PlaneBuffers.end(); it++) {
for (auto it = pendingBuffers.begin(); it != pendingBuffers.end(); it++) {
if (it->second.modified) {
// The current buffers can be freed after the flip completes
if (it->second.fbId) {
m_FbsToFreeAfterFlip.push_back(it->second.fbId);
drmModeRmFB(m_Fd, it->second.fbId);
it->second.fbId = 0;
}
if (it->second.dumbBufferHandle) {
m_DumbBufsToFreeAfterFlip.push_back(it->second.dumbBufferHandle);
struct drm_mode_destroy_dumb destroyBuf = {};
destroyBuf.handle = it->second.dumbBufferHandle;
drmIoctl(m_Fd, DRM_IOCTL_MODE_DESTROY_DUMB, &destroyBuf);
it->second.dumbBufferHandle = 0;
}
// The pending buffers become the active buffers for this FB
std::swap(it->second.fbId, it->second.pendingFbId);
std::swap(it->second.dumbBufferHandle, it->second.pendingDumbBuffer);
it->second.modified = false;
m_PlaneBuffers[it->first].fbId = it->second.pendingFbId;
m_PlaneBuffers[it->first].dumbBufferHandle = it->second.pendingDumbBuffer;
}
else if (it->second.fbId || it->second.dumbBufferHandle) {
// This FB wasn't modified in this commit, so the current buffers stay around
m_PlaneBuffers[it->first].fbId = it->second.fbId;
m_PlaneBuffers[it->first].dumbBufferHandle = it->second.dumbBufferHandle;
}
// NB: We swapped in a new plane buffers map which will clear the modified value.
// It's important that we don't try to clear it here because we might stomp on
// a flipPlane() performed by another thread that queued up another modification.
}
}
else {
@@ -535,10 +458,7 @@ class DrmRenderer : public IFFmpegRenderer {
errno);
}
// Free the atomic request
drmModeAtomicFree(m_AtomicReq);
m_AtomicReq = nullptr;
drmModeAtomicFree(req);
return ret;
}
@@ -546,66 +466,12 @@ class DrmRenderer : public IFFmpegRenderer {
return m_Atomic;
}
void waitForFlipCompletion() {
while (m_FlipPending) {
struct pollfd pfd = { .fd = m_Fd, .events = POLLIN, .revents = 0 };
if (poll(&pfd, 1, -1) > 0) {
drmHandleEvent(m_Fd, &m_EventCtx);
}
else {
SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
"poll() failed: %d",
errno);
break;
}
}
}
private:
static void pageFlipHandler(int fd, unsigned int sequence,
unsigned int tv_sec, unsigned int tv_usec,
void *user_data) {
DrmPropertySetter* me = (DrmPropertySetter*)user_data;
Q_UNUSED(fd);
Q_UNUSED(sequence);
Q_UNUSED(tv_sec);
Q_UNUSED(tv_usec);
{
std::lock_guard lg { me->m_Lock };
// Free any FBs and dumb buffers that are marked to free on page flip
for (auto it = me->m_FbsToFreeAfterFlip.begin(); it != me->m_FbsToFreeAfterFlip.end(); it++) {
drmModeRmFB(me->m_Fd, *it);
}
for (auto it = me->m_DumbBufsToFreeAfterFlip.begin(); it != me->m_DumbBufsToFreeAfterFlip.end(); it++) {
struct drm_mode_destroy_dumb destroyBuf = {};
destroyBuf.handle = *it;
drmIoctl(me->m_Fd, DRM_IOCTL_MODE_DESTROY_DUMB, &destroyBuf);
}
me->m_FbsToFreeAfterFlip.clear();
me->m_DumbBufsToFreeAfterFlip.clear();
}
SDL_assert(me->m_FlipPending);
me->m_FlipPending = false;
}
int m_Fd = -1;
bool m_Atomic = false;
bool m_AsyncFlip = false;
std::recursive_mutex m_Lock;
std::unordered_map<uint32_t, PlaneBuffer> m_PlaneBuffers;
// Flip event tracking
drmEventContext m_EventCtx;
bool m_FlipPending = false;
std::vector<uint32_t> m_FbsToFreeAfterFlip;
std::vector<uint32_t> m_DumbBufsToFreeAfterFlip;
// Legacy context
std::unordered_map<uint32_t, PlaneConfiguration> m_PlaneConfigs;