Hi Alex. On Tue, Apr 07, 2020 at 10:42:46AM -0400, Alex Deucher wrote: > On Mon, Apr 6, 2020 at 3:48 PM Sam Ravnborg <sam@xxxxxxxxxxxx> wrote: > > > > 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. > > For historical reference, the vertical blanking period was designed to > give the electron gun (on CRTs) enough time to move back to the top of > the screen to start scanning out the next frame. Similar for > horizontal blanking periods. They were designed to give the electron > gun enough time to move back to the other side of the screen to start > scanning the next scanline. Might be worth adding something like > that. Either way: > Reviewed-by: Alex Deucher <alexander.deucher@xxxxxxx> Thanks. Added this nice historical lesson and committed and pushed out. And to all, thanks for the inputs. We managed to improve this piece of the documetation. Sam > > > + * > > + * :: > > + * > > + * > > + * 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 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
