On Mon, 2020-04-06 at 21:47 +0200, Sam Ravnborg wrote:
Lyude Paul wrote a very good intro to vblank here: https://lore.kernel.org/dri-devel/faf63d8a9ed23c16af69762f59d0dca6b2bf085f.c...
Add this to the intro chapter in drm_vblank.c so others can benefit from it too.
v2:
- Reworded to improve readability (Thomas)
v3:
- Added nice ascii drawing from Lyude (Lyude)
- Added referende to high-precision timestamp (Daniel)
- Improved grammar (Thomas)
- Combined it all and made kernel-doc happy
- Dropped any a-b, r-b do to the amount of changes
Signed-off-by: Sam Ravnborg sam@ravnborg.org Co-developed-by: Lyude Paul lyude@redhat.com Cc: Lyude Paul lyude@redhat.com Cc: Thomas Zimmermann tzimmermann@suse.de Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Maxime Ripard mripard@kernel.org Cc: Thomas Zimmermann tzimmermann@suse.de Cc: David Airlie airlied@linux.ie
drivers/gpu/drm/drm_vblank.c | 53 ++++++++++++++++++++++++++++++++++++ 1 file changed, 53 insertions(+)
diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c index bcf346b3e486..9633092c9ad5 100644 --- a/drivers/gpu/drm/drm_vblank.c +++ b/drivers/gpu/drm/drm_vblank.c @@ -41,6 +41,59 @@ /**
- DOC: vblank handling
- From the computer's perspective, every time the monitor displays
- a new frame the scanout engine have "scanned out" the display image
- from top to bottom, one row of pixels at a time.
s/have/has/
Other then that:
Reviewed-by: Lyude Paul lyude@redhat.com
- The current row of pixels is referred to as the current scanline.
- In addition to the display's visible area, there's usually a couple of
- extra scanlines which aren't actually displayed on the screen.
- These extra scanlines don't contain image data and are occasionally used
- for features like audio and infoframes. The region made up of these
- scanlines is referred to as the vertical blanking region, or vblank for
- short.
- ::
- physical → ⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽
- top of | |
- display | |
| New frame |
| |
|↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓|
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| ← Scanline,updates
|↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓| the frame asit
| | travels down
| | ("scan out")
| |
| Old frame |
| |
| |
| |
| | physical
| | bottom of
- vertical |⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽| ← display
- blanking ┆xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx┆
- region → ┆xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx┆
┆xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx┆
- start of → ⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽
- new frame
- "Physical top of display" is the reference point for the high-precision/
- corrected timestamp.
- On a lot of display hardware, programming needs to take effect during
the
- vertical blanking period so that settings like gamma, the image buffer
- buffer to be scanned out, etc. can safely be changed without showing
- any visual artifacts on the screen. In some unforgiving hardware, some
of
- this programming has to both start and end in the same vblank.
- The vblank interrupt may be fired at different points depending on the
- hardware. Some hardware implementations will fire the interrupt when the
- new frame start, other implementations will fire the interrupt at
different
- points in time.
- 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