kernel/include/drm/drm_vblank.h, branch linux-rolling-stable

drm/vblank: Add vblank timer

2025-10-01T06:31:59Z

The vblank timer simulates a vblank interrupt for hardware without support. Rate-limits the display update frequency. DRM drivers for hardware without vblank support apply display updates ASAP. A vblank event informs DRM clients of the completed update. Userspace compositors immediately schedule the next update, which creates significant load on virtualization outputs. Display updates are usually fast on virtualization outputs, as their framebuffers are in regular system memory and there's no hardware vblank interrupt to throttle the update rate. The vblank timer is a HR timer that signals the vblank in software. It limits the update frequency of a DRM driver similar to a hardware vblank interrupt. The timer is not synchronized to the actual vblank interval of the display. The code has been adopted from vkms, which added the funtionality in commit 3a0709928b17 ("drm/vkms: Add vblank events simulated by hrtimers"). The new implementation is part of the existing vblank support, which sets up the timer automatically. Drivers only have to start and cancel the vblank timer as part of enabling and disabling the CRTC. The new vblank helper library provides callbacks for struct drm_crtc_funcs. The standard way for handling vblank is to call drm_crtc_handle_vblank(). Drivers that require additional processing, such as vkms, can init handle_vblank_timeout in struct drm_crtc_helper_funcs to refer to their timeout handler. There's a possible deadlock between drm_crtc_handle_vblank() and hrtimer_cancel(). [1] The implementation avoids to call hrtimer_cancel() directly and instead signals to the timer function to not restart itself. v4: - fix possible race condition between timeout and atomic commit (Michael) v3: - avoid deadlock when cancelling timer (Ville, Lyude) v2: - implement vblank timer entirely in vblank helpers - downgrade overrun warning to debug - fix docs Signed-off-by: Thomas Zimmermann Tested-by: Louis Chauvet Reviewed-by: Louis Chauvet Reviewed-by: Javier Martinez Canillas Tested-by: Michael Kelley Link: https://lore.kernel.org/all/20250510094757.4174662-1-zengheng4@huawei.com/ # [1] Link: https://lore.kernel.org/r/20250916083816.30275-2-tzimmermann@suse.de

drm/vblank: add dynamic per-crtc vblank configuration support

2024-07-26T21:40:10Z

We would like to be able to enable vblank_disable_immediate unconditionally, however there are a handful of cases where a small off delay is necessary (e.g. with PSR enabled). So, we would like to be able to adjust the vblank off delay and disable imminent values dynamically for a given CRTC. Since, it will allow drivers to apply static screen optimizations more quickly and consequently allow users to benefit more so from the power savings afforded by the aforementioned optimizations, while avoiding issues in cases where an off delay is still warranted. In particular, the PSR case requires a small off delay of 2 frames, otherwise display firmware isn't able to keep up with all of the requests made to amdgpu. So, introduce drm_crtc_vblank_on_config() which is like drm_crtc_vblank_on(), but it allows drivers to specify the vblank CRTC configuration before enabling vblanking support for a given CRTC. Signed-off-by: Hamza Mahfooz Acked-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20240725205109.209743-1-hamza.mahfooz@amd.com

drm/vblank: Introduce drm_crtc_vblank_crtc()

2024-04-18T10:27:56Z

Make life easier by providing a function that hands out the correct drm_vblank_crtc for a given a drm_crtc. Also abstract the lower level internals of the vblank code in a similar fashion. Signed-off-by: Ville Syrjälä Link: https://patchwork.freedesktop.org/patch/msgid/20240408190611.24914-1-ville.syrjala@linux.intel.com Reviewed-by: Dmitry Baryshkov

drm/vblank: Add helper to get next vblank time

2023-03-28T21:52:59Z

Will be used in the next commit to set a deadline on fences that an atomic update is waiting on. v2: Calculate time at *start* of vblank period, not end v3: Fix kbuild complaints Signed-off-by: Rob Clark Reviewed-by: Mario Kleiner

drm/vblank: Document drm_crtc_vblank_restore constraints

2021-02-10T11:38:55Z

I got real badly confused when trying to review a fix from Ville for this. Let's try to document better what's required for this, and check the minimal settings at runtime - we can't check ofc that there's indeed no races in the driver callback. Also noticed that the drm_vblank_restore version is unused, so lets unexport that while at it. Reviewed-by: Ville Syrjälä Cc: Ville Syrjala Signed-off-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20210209101523.2954281-1-daniel.vetter@ffwll.ch

drm/vblank: Add vblank works

2020-07-16T22:16:31Z

Add some kind of vblank workers. The interface is similar to regular delayed works, and is mostly based off kthread_work. It allows for scheduling delayed works that execute once a particular vblank sequence has passed. It also allows for accurate flushing of scheduled vblank works - in that flushing waits for both the vblank sequence and job execution to complete, or for the work to get cancelled - whichever comes first. Whatever hardware programming we do in the work must be fast (must at least complete during the vblank or scanout period, sometimes during the first few scanlines of the vblank). As such we use a high-priority per-CRTC thread to accomplish this. Changes since v7: * Stuff drm_vblank_internal.h and drm_vblank_work_internal.h contents into drm_internal.h * Get rid of unnecessary spinlock in drm_crtc_vblank_on() * Remove !vblank->worker check * Grab vbl_lock in drm_vblank_work_schedule() * Mention self-rearming work items in drm_vblank_work_schedule() kdocs * Return 1 from drm_vblank_work_schedule() if the work was scheduled successfully, 0 or error code otherwise * Use drm_dbg_core() instead of DRM_DEV_ERROR() in drm_vblank_work_schedule() * Remove vblank->worker checks in drm_vblank_destroy_worker() and drm_vblank_flush_worker() Changes since v6: * Get rid of ->pending and seqcounts, and implement flushing through simpler means - danvet * Get rid of work_lock, just use drm_device->event_lock * Move drm_vblank_work item cleanup into drm_crtc_vblank_off() so that we ensure that all vblank work has finished before disabling vblanks * Add checks into drm_crtc_vblank_reset() so we yell if it gets called while there's vblank workers active * Grab event_lock in both drm_crtc_vblank_on()/drm_crtc_vblank_off(), the main reason for this is so that other threads calling drm_vblank_work_schedule() are blocked from attempting to schedule while we're in the middle of enabling/disabling vblanks. * Move drm_handle_vblank_works() call below drm_handle_vblank_events() * Simplify drm_vblank_work_cancel_sync() * Fix drm_vblank_work_cancel_sync() documentation * Move wake_up_all() calls out of spinlock where we can. The only one I left was the call to wake_up_all() in drm_vblank_handle_works() as this seemed like it made more sense just living in that function (which is all technically under lock) * Move drm_vblank_work related functions into their own source files * Add drm_vblank_internal.h so we can export some functions we don't want drivers using, but that we do need to use in drm_vblank_work.c * Add a bunch of documentation Changes since v4: * Get rid of kthread interfaces we tried adding and move all of the locking into drm_vblank.c. For implementing drm_vblank_work_flush(), we now use a wait_queue and sequence counters in order to differentiate between multiple work item executions. * Get rid of drm_vblank_work_cancel() - this would have been pretty difficult to actually reimplement and it occurred to me that neither nouveau or i915 are even planning to use this function. Since there's also no async cancel function for most of the work interfaces in the kernel, it seems a bit unnecessary anyway. * Get rid of to_drm_vblank_work() since we now are also able to just pass the struct drm_vblank_work to work item callbacks anyway Changes since v3: * Use our own spinlocks, don't integrate so tightly with kthread_works Changes since v2: * Use kthread_workers instead of reinventing the wheel. Cc: Tejun Heo Cc: dri-devel@lists.freedesktop.org Cc: nouveau@lists.freedesktop.org Reviewed-by: Daniel Vetter Co-developed-by: Ville Syrjälä Signed-off-by: Lyude Paul Acked-by: Dave Airlie Link: https://patchwork.freedesktop.org/patch/msgid/20200627194657.156514-4-lyude@redhat.com

drm: Remove legacy version of get_scanout_position()

2020-02-13T12:10:10Z

The legacy version of get_scanout_position() was only useful while drivers still used drm_driver.get_scanout_position(). With no such drivers left, the related typedef and code can be removed Signed-off-by: Thomas Zimmermann Reviewed-by: Ville Syrjälä Link: https://patchwork.freedesktop.org/patch/msgid/20200123135943.24140-23-tzimmermann@suse.de

drm: Clean-up VBLANK-related callbacks in struct drm_driver

2020-02-13T12:10:10Z

All non-legacy users of VBLANK functions in struct drm_driver have been converted to use the respective interfaces in struct drm_crtc_funcs. The remaining users of VBLANK callbacks in struct drm_driver are legacy drivers with userspace modesetting. All users of struct drm_driver.get_scanout_position() have been converted to the respective CRTC helper function. Remove the callback from struct drm_driver. There are no users left of get_vblank_timestamp(), so the callback is being removed. The other VBLANK callbacks are being moved to the legacy section at the end of struct drm_driver. Also removed is drm_calc_vbltimestamp_from_scanoutpos(). Callers of this function have been converted to use the CRTC instead. v4: * more readable code for setting high_prec (Ville, Jani) v2: * merge with removal of struct drm_driver.get_scanout_position() * remove drm_calc_vbltimestamp_from_scanoutpos() Signed-off-by: Thomas Zimmermann Reviewed-by: Daniel Vetter Tested-by: Yannick Fertré Link: https://patchwork.freedesktop.org/patch/msgid/20200123135943.24140-22-tzimmermann@suse.de

drm: Add get_vblank_timestamp() to struct drm_crtc_funcs

2020-02-13T12:08:13Z

The callback get_vblank_timestamp() is currently located in struct drm_driver, but really belongs into struct drm_crtc_funcs. Add an equivalent there. Driver will be converted in separate patches. The default implementation is drm_calc_vbltimestamp_from_scanoutpos(). The patch adds drm_crtc_vblank_helper_get_vblank_timestamp(), which is an implementation for the CRTC callback. v4: * more readable code for setting high_prec (Ville, Jani) v3: * use refactored timestamp calculation to minimize duplicated code * do more checks for crtc != NULL to support legacy drivers v2: * rename helper to drm_crtc_vblank_helper_get_vblank_timestamp() * replace drm_calc_vbltimestamp_from_scanoutpos() with drm_crtc_vblank_helper_get_vblank_timestamp() in docs Signed-off-by: Thomas Zimmermann Reviewed-by: Ville Syrjälä Link: https://patchwork.freedesktop.org/patch/msgid/20200123135943.24140-4-tzimmermann@suse.de

drm: Add get_scanout_position() to struct drm_crtc_helper_funcs

2020-02-13T12:08:13Z

The new callback get_scanout_position() reads the current location of the scanout process. The operation is currently located in struct drm_driver, but really belongs to the CRTC. Drivers will be converted in separate patches. To help with the conversion, the timestamp calculation has been moved from drm_calc_vbltimestamp_from_scanoutpos() to drm_crtc_vblank_helper_get_vblank_timestamp_internal(). The helper function supports the new and old interface of get_scanout_position(). drm_calc_vbltimestamp_from_scanoutpos() remains as a wrapper around the new function. Callback functions return the scanout position from the CRTC. The legacy version of the interface receives the device and pipe index, the modern version receives a pointer to the CRTC. We keep the legacy version until all drivers have been converted. v4: * 80-character line fixes v3: * refactor drm_calc_vbltimestamp_from_scanoutpos() to minimize code duplication * define types for get_scanout_position() callbacks v2: * fix logical op in drm_calc_vbltimestamp_from_scanoutpos() Signed-off-by: Thomas Zimmermann Tested-by: Yannick Fertré Reviewed-by: Ville Syrjälä Link: https://patchwork.freedesktop.org/patch/msgid/20200123135943.24140-3-tzimmermann@suse.de