Lyude Paul wrote a very good intro to vblank here: https://lore.kernel.org/dri-devel/faf63d8a9ed23c16af69762f59d0dca6b2bf085f.camel@xxxxxxxxxx/T/#mce6480be738160e9d07c5d023e88fd78d7a06d27 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@xxxxxxxxxxxx> Co-developed-by: Lyude Paul <lyude@xxxxxxxxxx> Cc: Lyude Paul <lyude@xxxxxxxxxx> Cc: Thomas Zimmermann <tzimmermann@xxxxxxx> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx> Cc: Maxime Ripard <mripard@xxxxxxxxxx> Cc: Thomas Zimmermann <tzimmermann@xxxxxxx> Cc: David Airlie <airlied@xxxxxxxx> --- 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. + * 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 as it + * | | 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 -- 2.20.1 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
