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backend/drm: implement KMS state snapshot/restore

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Following ideas from [1], snapshot the entire KMS state when the VT
is switched away, and restore it when the VT is switched back.

> Well the neat trick is that userspace doesn’t need to be able to
> understand properties to save and restore them - the actual property
> value transport between kernel and userspace is fully generic.

That way, even if another DRM master changes a property we don't
understand like CTM or HDR_OUTPUT_METADATA, we can switch it back
and avoid getting garbage on screen.

[1]: https://blog.ffwll.ch/2016/01/vt-switching-with-atomic-modeset.html
This commit is contained in:
Simon Ser 2022-10-18 18:23:55 +02:00
parent e0b2bf2a6b
commit f0bb53c4ab
7 changed files with 155 additions and 20 deletions
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84
backend/drm/util.c
View file

@ -276,3 +276,87 @@ size_t match_obj(size_t num_objs, const uint32_t objs[static restrict num_objs],
match_obj_(&st, 0, 0, 0, 0);
return st.score;
}
static bool snapshot_drm_object(int drm_fd, drmModeAtomicReq *req,
uint32_t object_id) {
drmModeObjectProperties *props =
drmModeObjectGetProperties(drm_fd, object_id, DRM_MODE_OBJECT_ANY);
if (props == NULL) {
wlr_log_errno(WLR_ERROR, "drmModeObjectGetProperties failed");
return false;
}
bool ok = true;
for (uint32_t i = 0; i < props->count_props; i++) {
uint32_t prop_id = props->props[i];
uint64_t value = props->prop_values[i];
drmModePropertyRes *prop = drmModeGetProperty(drm_fd, prop_id);
if (prop == NULL) {
wlr_log_errno(WLR_ERROR, "drmModeGetProperty failed");
ok = false;
break;
}
bool immutable = prop->flags & DRM_MODE_PROP_IMMUTABLE;
bool dpms = strcmp(prop->name, "DPMS") == 0;
drmModeFreeProperty(prop);
if (immutable || dpms) {
// DPMS is a bit special: it can only be set from the legacy uAPI. Restoring it from the
// atomic uAPI will fail.
continue;
}
if (drmModeAtomicAddProperty(req, object_id, prop_id, value) < 0) {
wlr_log_errno(WLR_ERROR, "drmModeAtomicAddProperty failed");
ok = false;
break;
}
}
drmModeFreeObjectProperties(props);
return ok;
}
drmModeAtomicReq *snapshot_drm_state(int drm_fd) {
drmModeAtomicReq *req = drmModeAtomicAlloc();
if (req == NULL) {
wlr_log_errno(WLR_ERROR, "drmModeAtomicAlloc failed");
return false;
}
bool ok = true;
drmModeRes *res = drmModeGetResources(drm_fd);
if (res == NULL) {
wlr_log_errno(WLR_ERROR, "drmModeGetResources failed");
goto error;
}
for (int i = 0; i < res->count_crtcs; i++) {
ok = ok && snapshot_drm_object(drm_fd, req, res->crtcs[i]);
}
for (int i = 0; i < res->count_connectors; i++) {
ok = ok && snapshot_drm_object(drm_fd, req, res->connectors[i]);
}
drmModeFreeResources(res);
if (!ok) {
goto error;
}
drmModePlaneRes *planes = drmModeGetPlaneResources(drm_fd);
if (planes == NULL) {
wlr_log_errno(WLR_ERROR, "drmModeGetPlaneResources failed");
return false;
}
for (uint32_t i = 0; i < planes->count_planes; i++) {
ok = ok && snapshot_drm_object(drm_fd, req, planes->planes[i]);
}
drmModeFreePlaneResources(planes);
if (!ok) {
goto error;
}
return req;
error:
drmModeAtomicFree(req);
return NULL;
}