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74afeb8128
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 3a0709928b ("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 <tzimmermann@suse.de>
Tested-by: Louis Chauvet <louis.chauvet@bootlin.com>
Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Tested-by: Michael Kelley <mhklinux@outlook.com>
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
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=============================
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Mode Setting Helper Functions
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=============================
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The DRM subsystem aims for a strong separation between core code and helper
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libraries. Core code takes care of general setup and teardown and decoding
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userspace requests to kernel internal objects. Everything else is handled by a
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large set of helper libraries, which can be combined freely to pick and choose
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for each driver what fits, and avoid shared code where special behaviour is
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needed.
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This distinction between core code and helpers is especially strong in the
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modesetting code, where there's a shared userspace ABI for all drivers. This is
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in contrast to the render side, where pretty much everything (with very few
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exceptions) can be considered optional helper code.
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There are a few areas these helpers can grouped into:
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* Helpers to implement modesetting. The important ones here are the atomic
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helpers. Old drivers still often use the legacy CRTC helpers. They both share
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the same set of common helper vtables. For really simple drivers (anything
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that would have been a great fit in the deprecated fbdev subsystem) there's
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also the simple display pipe helpers.
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* There's a big pile of helpers for handling outputs. First the generic bridge
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helpers for handling encoder and transcoder IP blocks. Second the panel helpers
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for handling panel-related information and logic. Plus then a big set of
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helpers for the various sink standards (DisplayPort, HDMI, MIPI DSI). Finally
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there's also generic helpers for handling output probing, and for dealing with
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EDIDs.
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* The last group of helpers concerns itself with the frontend side of a display
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pipeline: Planes, handling rectangles for visibility checking and scissoring,
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flip queues and assorted bits.
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Modeset Helper Reference for Common Vtables
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===========================================
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.. kernel-doc:: include/drm/drm_modeset_helper_vtables.h
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:doc: overview
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.. kernel-doc:: include/drm/drm_modeset_helper_vtables.h
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:internal:
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.. _drm_atomic_helper:
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Atomic Modeset Helper Functions Reference
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=========================================
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Overview
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--------
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.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
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:doc: overview
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Implementing Asynchronous Atomic Commit
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---------------------------------------
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.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
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:doc: implementing nonblocking commit
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Helper Functions Reference
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--------------------------
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.. kernel-doc:: include/drm/drm_atomic_helper.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c
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:export:
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Atomic State Reset and Initialization
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-------------------------------------
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.. kernel-doc:: drivers/gpu/drm/drm_atomic_state_helper.c
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:doc: atomic state reset and initialization
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Atomic State Helper Reference
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-----------------------------
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.. kernel-doc:: drivers/gpu/drm/drm_atomic_state_helper.c
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:export:
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GEM Atomic Helper Reference
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---------------------------
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.. kernel-doc:: drivers/gpu/drm/drm_gem_atomic_helper.c
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:doc: overview
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.. kernel-doc:: include/drm/drm_gem_atomic_helper.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_gem_atomic_helper.c
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:export:
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VBLANK Helper Reference
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-----------------------
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.. kernel-doc:: drivers/gpu/drm/drm_vblank_helper.c
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:doc: overview
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.. kernel-doc:: include/drm/drm_vblank_helper.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_vblank_helper.c
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:export:
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Simple KMS Helper Reference
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===========================
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.. kernel-doc:: drivers/gpu/drm/drm_simple_kms_helper.c
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:doc: overview
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.. kernel-doc:: include/drm/drm_simple_kms_helper.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_simple_kms_helper.c
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:export:
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fbdev Helper Functions Reference
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================================
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.. kernel-doc:: drivers/gpu/drm/drm_fb_helper.c
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:doc: fbdev helpers
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.. kernel-doc:: include/drm/drm_fb_helper.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_fb_helper.c
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:export:
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format Helper Functions Reference
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=================================
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.. kernel-doc:: drivers/gpu/drm/drm_format_helper.c
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:export:
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Framebuffer DMA Helper Functions Reference
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==========================================
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.. kernel-doc:: drivers/gpu/drm/drm_fb_dma_helper.c
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:doc: framebuffer dma helper functions
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.. kernel-doc:: drivers/gpu/drm/drm_fb_dma_helper.c
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:export:
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Framebuffer GEM Helper Reference
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================================
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.. kernel-doc:: drivers/gpu/drm/drm_gem_framebuffer_helper.c
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:doc: overview
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.. kernel-doc:: drivers/gpu/drm/drm_gem_framebuffer_helper.c
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:export:
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.. _drm_bridges:
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Bridges
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=======
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Overview
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--------
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.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
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:doc: overview
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Display Driver Integration
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--------------------------
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.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
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:doc: display driver integration
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Special Care with MIPI-DSI bridges
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----------------------------------
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.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
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:doc: special care dsi
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Bridge Operations
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-----------------
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.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
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:doc: bridge operations
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Bridge Connector Helper
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-----------------------
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.. kernel-doc:: drivers/gpu/drm/display/drm_bridge_connector.c
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:doc: overview
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Bridge Helper Reference
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-------------------------
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.. kernel-doc:: include/drm/drm_bridge.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
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:export:
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MIPI-DSI bridge operation
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-------------------------
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.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
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:doc: dsi bridge operations
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Bridge Connector Helper Reference
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---------------------------------
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.. kernel-doc:: drivers/gpu/drm/display/drm_bridge_connector.c
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:export:
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Panel-Bridge Helper Reference
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-----------------------------
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.. kernel-doc:: drivers/gpu/drm/bridge/panel.c
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:export:
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.. _drm_panel_helper:
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Panel Helper Reference
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======================
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.. kernel-doc:: drivers/gpu/drm/drm_panel.c
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:doc: drm panel
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.. kernel-doc:: include/drm/drm_panel.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_panel.c
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:export:
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.. kernel-doc:: drivers/gpu/drm/drm_panel_orientation_quirks.c
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:export:
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.. kernel-doc:: drivers/gpu/drm/drm_panel_backlight_quirks.c
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:export:
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Panel Self Refresh Helper Reference
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===================================
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.. kernel-doc:: drivers/gpu/drm/drm_self_refresh_helper.c
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:doc: overview
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.. kernel-doc:: drivers/gpu/drm/drm_self_refresh_helper.c
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:export:
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HDMI Atomic State Helpers
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=========================
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Overview
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--------
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.. kernel-doc:: drivers/gpu/drm/display/drm_hdmi_state_helper.c
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:doc: hdmi helpers
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Functions Reference
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-------------------
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.. kernel-doc:: drivers/gpu/drm/display/drm_hdmi_state_helper.c
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:export:
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HDCP Helper Functions Reference
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===============================
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.. kernel-doc:: drivers/gpu/drm/display/drm_hdcp_helper.c
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:export:
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Display Port Helper Functions Reference
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=======================================
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.. kernel-doc:: drivers/gpu/drm/display/drm_dp_helper.c
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:doc: dp helpers
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.. kernel-doc:: include/drm/display/drm_dp.h
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:internal:
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.. kernel-doc:: include/drm/display/drm_dp_helper.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/display/drm_dp_helper.c
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:export:
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Display Port CEC Helper Functions Reference
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===========================================
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.. kernel-doc:: drivers/gpu/drm/display/drm_dp_cec.c
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:doc: dp cec helpers
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.. kernel-doc:: drivers/gpu/drm/display/drm_dp_cec.c
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:export:
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Display Port Dual Mode Adaptor Helper Functions Reference
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=========================================================
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.. kernel-doc:: drivers/gpu/drm/display/drm_dp_dual_mode_helper.c
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:doc: dp dual mode helpers
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.. kernel-doc:: include/drm/display/drm_dp_dual_mode_helper.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/display/drm_dp_dual_mode_helper.c
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:export:
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Display Port MST Helpers
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========================
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Overview
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--------
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.. kernel-doc:: drivers/gpu/drm/display/drm_dp_mst_topology.c
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:doc: dp mst helper
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.. kernel-doc:: drivers/gpu/drm/display/drm_dp_mst_topology.c
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:doc: Branch device and port refcounting
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Functions Reference
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-------------------
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.. kernel-doc:: include/drm/display/drm_dp_mst_helper.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/display/drm_dp_mst_topology.c
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:export:
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Topology Lifetime Internals
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---------------------------
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These functions aren't exported to drivers, but are documented here to help make
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the MST topology helpers easier to understand
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.. kernel-doc:: drivers/gpu/drm/display/drm_dp_mst_topology.c
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:functions: drm_dp_mst_topology_try_get_mstb drm_dp_mst_topology_get_mstb
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drm_dp_mst_topology_put_mstb
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drm_dp_mst_topology_try_get_port drm_dp_mst_topology_get_port
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drm_dp_mst_topology_put_port
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drm_dp_mst_get_mstb_malloc drm_dp_mst_put_mstb_malloc
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MIPI DBI Helper Functions Reference
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===================================
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.. kernel-doc:: drivers/gpu/drm/drm_mipi_dbi.c
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:doc: overview
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.. kernel-doc:: include/drm/drm_mipi_dbi.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_mipi_dbi.c
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:export:
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MIPI DSI Helper Functions Reference
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===================================
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.. kernel-doc:: drivers/gpu/drm/drm_mipi_dsi.c
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:doc: dsi helpers
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.. kernel-doc:: include/drm/drm_mipi_dsi.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_mipi_dsi.c
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:export:
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Display Stream Compression Helper Functions Reference
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=====================================================
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.. kernel-doc:: drivers/gpu/drm/display/drm_dsc_helper.c
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:doc: dsc helpers
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.. kernel-doc:: include/drm/display/drm_dsc.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/display/drm_dsc_helper.c
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:export:
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Output Probing Helper Functions Reference
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=========================================
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.. kernel-doc:: drivers/gpu/drm/drm_probe_helper.c
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:doc: output probing helper overview
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.. kernel-doc:: drivers/gpu/drm/drm_probe_helper.c
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:export:
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EDID Helper Functions Reference
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===============================
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.. kernel-doc:: include/drm/drm_edid.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_edid.c
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:export:
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.. kernel-doc:: include/drm/drm_eld.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_eld.c
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:export:
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SCDC Helper Functions Reference
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===============================
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.. kernel-doc:: drivers/gpu/drm/display/drm_scdc_helper.c
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:doc: scdc helpers
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.. kernel-doc:: include/drm/display/drm_scdc_helper.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/display/drm_scdc_helper.c
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:export:
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HDMI Infoframes Helper Reference
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================================
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Strictly speaking this is not a DRM helper library but generally usable
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by any driver interfacing with HDMI outputs like v4l or alsa drivers.
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But it nicely fits into the overall topic of mode setting helper
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libraries and hence is also included here.
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.. kernel-doc:: include/linux/hdmi.h
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:internal:
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.. kernel-doc:: drivers/video/hdmi.c
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:export:
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Rectangle Utilities Reference
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=============================
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.. kernel-doc:: include/drm/drm_rect.h
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:doc: rect utils
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.. kernel-doc:: include/drm/drm_rect.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_rect.c
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:export:
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Flip-work Helper Reference
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==========================
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.. kernel-doc:: include/drm/drm_flip_work.h
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:doc: flip utils
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.. kernel-doc:: include/drm/drm_flip_work.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_flip_work.c
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:export:
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Auxiliary Modeset Helpers
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=========================
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.. kernel-doc:: drivers/gpu/drm/drm_modeset_helper.c
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:doc: aux kms helpers
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.. kernel-doc:: drivers/gpu/drm/drm_modeset_helper.c
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:export:
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OF/DT Helpers
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=============
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.. kernel-doc:: drivers/gpu/drm/drm_of.c
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:doc: overview
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.. kernel-doc:: drivers/gpu/drm/drm_of.c
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:export:
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Legacy Plane Helper Reference
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=============================
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.. kernel-doc:: drivers/gpu/drm/drm_plane_helper.c
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:doc: overview
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.. kernel-doc:: drivers/gpu/drm/drm_plane_helper.c
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:export:
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Legacy CRTC/Modeset Helper Functions Reference
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==============================================
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.. kernel-doc:: drivers/gpu/drm/drm_crtc_helper.c
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:doc: overview
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.. kernel-doc:: drivers/gpu/drm/drm_crtc_helper.c
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:export:
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Privacy-screen class
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====================
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.. kernel-doc:: drivers/gpu/drm/drm_privacy_screen.c
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:doc: overview
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.. kernel-doc:: include/drm/drm_privacy_screen_driver.h
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:internal:
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.. kernel-doc:: include/drm/drm_privacy_screen_machine.h
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:internal:
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.. kernel-doc:: drivers/gpu/drm/drm_privacy_screen.c
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:export:
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