Quoting Dawid Kurek (2017-07-07 06:48:49)
In page_flip vblank is sent with no delay. Driver does not know when the actual update is present on the display and has no means for getting this information from a device. It is practically impossible to say exactly *when* as there is also i.e. a usb delay.
When we are unable to determine when the vblank actually happens we may assume it will behave accordingly, i.e. it will present frames with proper timing. In the worst case scenario it should take up to duration of one frame (we may get new frame in the device just after presenting current one so we would need to wait for the whole frame).
Because of the asynchronous nature of the delay we need to synchronize:
- read/write vrefresh/page_flip data when changing mode and preparing/executing vblank
- USB requests to prevent interleaved access to URBs for two different frame buffers
All those changes are backports from ChromeOS:
- https://chromium-review.googlesource.com/250622
- https://chromium-review.googlesource.com/249450 partially, only change in udl_modeset.c for 'udl_flip_queue'
- https://chromium-review.googlesource.com/321378
- https://chromium-review.googlesource.com/324119
- fixes for checkpatch and latest drm changes
Cc: hshi@chromium.org Cc: marcheu@chromium.org Cc: zachr@chromium.org Cc: dbehr@google.com Signed-off-by: Dawid Kurek dawid.kurek@displaylink.com
+struct udl_flip_queue {
struct mutex lock;struct workqueue_struct *wq;struct delayed_work work;struct drm_crtc *crtc;struct drm_pending_vblank_event *event;u64 flip_time; /*in jiffies */u64 vblank_interval; /*in jiffies */
jiffies are unsigned long. That avoids the complication of the reader having to consider whether all the divides are 32bit safe.
mallocing this struct seems a little overkill as opposed to embedding it tino the udl_device, flip_queue.wq provides the safety check after initialisation.
I couldn't spot anything drastically wrong, certainly it looks complete, I would have structured it such that everything went through the same worker with a hrtimer emulating the vblank. That model is then but a stone's throw away from atomic.
Reviewed-by: Chris Wilson chris@chris-wilson.co.uk -Chris