Skip to content

fable findings #138

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
henkwiedig merged 1 commit into from
Jul 11, 2026
Merged

fable findings #138

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
49 changes: 41 additions & 8 deletions src/drm.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -458,6 +458,24 @@ void modeset_output_destroy(int fd, struct modeset_output *out)
free(out);
}

// Exact refresh rate in millihertz derived from the pixel clock. The integer
// vrefresh field rounds 59.94 and 60.00 to the same value, so it cannot be
// used to tell them apart.
static uint32_t mode_refresh_mhz(const drmModeModeInfo *m)
{
if (!m->htotal || !m->vtotal)
return 0;
uint64_t num = (uint64_t)m->clock * 1000000;
uint64_t den = (uint64_t)m->htotal * m->vtotal;
if (m->flags & DRM_MODE_FLAG_INTERLACE)
num *= 2;
if (m->flags & DRM_MODE_FLAG_DBLSCAN)
den *= 2;
if (m->vscan > 1)
den *= m->vscan;
return (uint32_t)(num / den);
}

struct modeset_output *modeset_output_create(int fd, drmModeRes *res, drmModeConnector *conn, uint16_t mode_width, uint16_t mode_height, uint32_t mode_vrefresh, uint32_t video_plane_id, uint32_t osd_plane_id, float video_scale_factor)
{
int ret;
Expand All @@ -484,17 +502,28 @@ struct modeset_output *modeset_output_create(int fd, drmModeRes *res, drmModeCon
int preferred_fc = -1;
if (mode_width>0 && mode_height>0 && mode_vrefresh>0) {
fc = -1;
int fc_progressive = 0;
uint32_t fc_diff_mhz = UINT32_MAX;
printf( "Available modes:\n");
for (int i = 0; i < conn->count_modes; i++ ) {
printf( "%d : %dx%d@%d\n",i, conn->modes[i].hdisplay, conn->modes[i].vdisplay , conn->modes[i].vrefresh );
uint32_t refresh_mhz = mode_refresh_mhz(&conn->modes[i]);
printf( "%d : %dx%d@%d (%u.%03u Hz)\n",i, conn->modes[i].hdisplay, conn->modes[i].vdisplay , conn->modes[i].vrefresh, refresh_mhz / 1000, refresh_mhz % 1000 );
if (conn->modes[i].hdisplay == mode_width &&
conn->modes[i].vdisplay == mode_height &&
conn->modes[i].vrefresh == mode_vrefresh
) {
if (fc < 0)
fc = i;
if (fc >= 0 && (conn->modes[i].flags & DRM_MODE_FLAG_INTERLACE) == 0) // prefer progressive modes
// Prefer progressive modes; among equals, pick the mode whose
// exact refresh is closest to the requested rate, so eg @60
// selects 60.000 Hz and not 59.940 Hz (both have vrefresh 60).
int progressive = (conn->modes[i].flags & DRM_MODE_FLAG_INTERLACE) == 0;
uint32_t target_mhz = mode_vrefresh * 1000;
uint32_t diff_mhz = refresh_mhz > target_mhz ? refresh_mhz - target_mhz : target_mhz - refresh_mhz;
if (fc < 0 || (progressive && !fc_progressive) ||
(progressive == fc_progressive && diff_mhz < fc_diff_mhz)) {
fc = i;
fc_progressive = progressive;
fc_diff_mhz = diff_mhz;
}
} else if (conn->modes[i].type & DRM_MODE_TYPE_PREFERRED) {
preferred_fc = i;
}
Expand All @@ -506,7 +535,8 @@ struct modeset_output *modeset_output_create(int fd, drmModeRes *res, drmModeCon
fprintf(stderr, "couldn't find a matching mode, useing preferred mode %dx%d@%d\n", conn->modes[preferred_fc].hdisplay, conn->modes[preferred_fc].vdisplay , conn->modes[preferred_fc].vrefresh);
fc = preferred_fc;
}
printf( "Using screen mode %dx%d@%d\n",conn->modes[fc].hdisplay, conn->modes[fc].vdisplay , conn->modes[fc].vrefresh );
uint32_t used_mhz = mode_refresh_mhz(&conn->modes[fc]);
printf( "Using screen mode %dx%d@%d (%u.%03u Hz)\n",conn->modes[fc].hdisplay, conn->modes[fc].vdisplay , conn->modes[fc].vrefresh, used_mhz / 1000, used_mhz % 1000 );
}
memcpy(&out->mode, &conn->modes[fc], sizeof(out->mode));
if (drmModeCreatePropertyBlob(fd, &out->mode, sizeof(out->mode), &out->mode_blob_id) != 0) {
Expand Down Expand Up @@ -586,13 +616,16 @@ void *modeset_print_modes(int fd)
}
for (int i = 0; i < conn->count_modes; i++ ) {
info = conn->modes[i];
uint32_t refresh_mhz = mode_refresh_mhz(&info);
// Assuming modes list is sorted
if (info.hdisplay == prev_h && info.vdisplay == prev_v && info.vrefresh == prev_refresh)
if (info.hdisplay == prev_h && info.vdisplay == prev_v && refresh_mhz == prev_refresh)
continue;
printf("%dx%d@%d\n", info.hdisplay, info.vdisplay, info.vrefresh);
printf("%dx%d@%d (%u.%03u Hz%s)\n", info.hdisplay, info.vdisplay, info.vrefresh,
refresh_mhz / 1000, refresh_mhz % 1000,
(info.flags & DRM_MODE_FLAG_INTERLACE) ? ", interlaced" : "");
prev_h = info.hdisplay;
prev_v = info.vdisplay;
prev_refresh = info.vrefresh;
prev_refresh = refresh_mhz;
at_least_one = 1;
}
drmModeFreeConnector(conn);
Expand Down
27 changes: 22 additions & 5 deletions src/main.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -397,7 +397,8 @@ void *__FRAME_THREAD__(void *param)

void *__DISPLAY_THREAD__(void *param)
{
int ret;
int ret;
SchedulingHelper::set_thread_params_max_realtime("DISPLAY_THREAD",SchedulingHelper::PRIORITY_REALTIME_MID);
pthread_setname_np(pthread_self(), "__DISPLAY");

while (!frm_eos) {
Expand Down Expand Up @@ -431,7 +432,10 @@ void *__DISPLAY_THREAD__(void *param)
// show DRM FB in plane
uint32_t flags = DRM_MODE_ATOMIC_NONBLOCK;
if (fb_id != 0) {
flags = disable_vsync ? DRM_MODE_ATOMIC_NONBLOCK : DRM_MODE_ATOMIC_ALLOW_MODESET;
// Steady-state flips only update plane FB_IDs — no modeset is
// needed, so commit with flags=0 (blocking, vsynced) instead of
// ALLOW_MODESET, which permits heavier driver validation paths.
flags = disable_vsync ? DRM_MODE_ATOMIC_NONBLOCK : 0;
ret = set_drm_object_property(output_list->video_request, &output_list->video_plane, "FB_ID", fb_id);
assert(ret>0);
}
Expand All @@ -445,9 +449,22 @@ void *__DISPLAY_THREAD__(void *param)
ret = set_drm_object_property(output_list->video_request, &output_list->osd_plane, "FB_ID", output_list->osd_bufs[output_list->osd_buf_switch].fb);
assert(ret>0);
}
drmModeAtomicCommit(drm_fd, output_list->video_request, flags, NULL);
int commit_ret = drmModeAtomicCommit(drm_fd, output_list->video_request, flags, NULL);
ret = pthread_mutex_unlock(&osd_mutex);
assert(!ret);
if (commit_ret) {
if (commit_ret == -EBUSY && (flags & DRM_MODE_ATOMIC_NONBLOCK)) {
// Previous flip still pending — this frame is dropped.
spdlog::debug("Atomic commit EBUSY, frame dropped");
} else {
static uint64_t last_commit_warn_ms = 0;
uint64_t warn_now = get_time_ms();
if (warn_now - last_commit_warn_ms > 1000) {
last_commit_warn_ms = warn_now;
spdlog::warn("drmModeAtomicCommit failed: {}", commit_ret);
}
}
}
osd_publish_uint_fact("video.displayed_frame", NULL, 0, 1);
uint64_t decode_and_handover_display_ms=get_time_ms()-decoding_pts;
osd_publish_uint_fact("video.decode_and_handover_ms", NULL, 0, decode_and_handover_display_ms);
Expand Down Expand Up @@ -983,11 +1000,11 @@ void read_gstreamerpipe_stream(MppPacket *packet, int gst_udp_port, const char *
uint64_t period_start=0;
auto cb=[&packet,/*&decoder_stalled_count,*/ &bytes_received, &period_start](std::shared_ptr<std::vector<uint8_t>> frame){
// Let the gst pull thread run at quite high priority
static bool first= false;
static bool first= true;
static int stall_count = 0;
static uint64_t last_stall_idr_ms = 0;
if(first){
SchedulingHelper::set_thread_params_max_realtime("DisplayThread",SchedulingHelper::PRIORITY_REALTIME_LOW);
SchedulingHelper::set_thread_params_max_realtime("GstPullThread",SchedulingHelper::PRIORITY_REALTIME_LOW);
first= false;
}
bytes_received += frame->size();
Expand Down