diff options
Diffstat (limited to 'Documentation/gpu')
| -rw-r--r-- | Documentation/gpu/drm-kms.rst | 56 |
1 files changed, 2 insertions, 54 deletions
diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst index 0749000ab3d7..307284125d7a 100644 --- a/Documentation/gpu/drm-kms.rst +++ b/Documentation/gpu/drm-kms.rst @@ -551,60 +551,8 @@ various modules/drivers. Vertical Blanking ================= -Vertical blanking plays a major role in graphics rendering. To achieve -tear-free display, users must synchronize page flips and/or rendering to -vertical blanking. The DRM API offers ioctls to perform page flips -synchronized to vertical blanking and wait for vertical blanking. - -The DRM core handles most of the vertical blanking management logic, -which involves filtering out spurious interrupts, keeping race-free -blanking counters, coping with counter wrap-around and resets and -keeping use counts. It relies on the driver to generate vertical -blanking interrupts and optionally provide a hardware vertical blanking -counter. Drivers must implement the following operations. - -- int (\*enable_vblank) (struct drm_device \*dev, int crtc); void - (\*disable_vblank) (struct drm_device \*dev, int crtc); - Enable or disable vertical blanking interrupts for the given CRTC. - -- u32 (\*get_vblank_counter) (struct drm_device \*dev, int crtc); - Retrieve the value of the vertical blanking counter for the given - CRTC. If the hardware maintains a vertical blanking counter its value - should be returned. Otherwise drivers can use the - :c:func:`drm_vblank_count()` helper function to handle this - operation. - -Drivers must initialize the vertical blanking handling core with a call -to :c:func:`drm_vblank_init()` in their load operation. - -Vertical blanking interrupts can be enabled by the DRM core or by -drivers themselves (for instance to handle page flipping operations). -The DRM core maintains a vertical blanking use count to ensure that the -interrupts are not disabled while a user still needs them. To increment -the use count, drivers call :c:func:`drm_vblank_get()`. Upon -return vertical blanking interrupts are guaranteed to be enabled. - -To decrement the use count drivers call -:c:func:`drm_vblank_put()`. Only when the use count drops to zero -will the DRM core disable the vertical blanking interrupts after a delay -by scheduling a timer. The delay is accessible through the -vblankoffdelay module parameter or the ``drm_vblank_offdelay`` global -variable and expressed in milliseconds. Its default value is 5000 ms. -Zero means never disable, and a negative value means disable -immediately. Drivers may override the behaviour by setting the -:c:type:`struct drm_device <drm_device>` -vblank_disable_immediate flag, which when set causes vblank interrupts -to be disabled immediately regardless of the drm_vblank_offdelay -value. The flag should only be set if there's a properly working -hardware vblank counter present. - -When a vertical blanking interrupt occurs drivers only need to call the -:c:func:`drm_handle_vblank()` function to account for the -interrupt. - -Resources allocated by :c:func:`drm_vblank_init()` must be freed -with a call to :c:func:`drm_vblank_cleanup()` in the driver unload -operation handler. +.. kernel-doc:: drivers/gpu/drm/drm_vblank.c + :doc: vblank handling Vertical Blanking and Interrupt Handling Functions Reference ------------------------------------------------------------ |