Am 06.04.20 um 21:47 schrieb Sam Ravnborg: > 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> Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx> > --- > 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 > -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer
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