Re: [PATCH v1 1/6] drm/vblank: Add intro to documentation

[Sam Ravnborg <sam@ravnborg.org>]

Hi Thomas.

On Mon, Mar 30, 2020 at 01:29:16PM +0200, Thomas Zimmermann wrote:
> Hi Sam and Lyude,
> 
> thanks for improving the documentation. Below are a few points that I'd
> found more understandable. I'm no native speaker, though.
> 
> Am 28.03.20 um 14:20 schrieb Sam Ravnborg:
> > Lyude Paul wrote a very good intro to vblank here:
> > https://lore.kernel.org/dri-devel/faf63d8a9ed23c16af69762f59d0dca6b2bf085f.camel@redhat.com/T/#mce6480be738160e9d07c5d023e88fd78d7a06d27
> > 
> > Add this to the intro chapter in drm_vblank.c so others
> > can benefit from it too.
> > 
> > Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
> > Co-developed-by: Lyude Paul <lyude@redhat.com>
> > Cc: Lyude Paul <lyude@redhat.com>
> > Cc: Daniel Vetter <daniel@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 | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> > index bcf346b3e486..95cac22d59d1 100644
> > --- a/drivers/gpu/drm/drm_vblank.c
> > +++ b/drivers/gpu/drm/drm_vblank.c
> > @@ -41,6 +41,21 @@
> >  /**
> >   * DOC: vblank handling
> >   *
> > + * From the perspective of a computer, every time a computer monitor displays
> 
> Possibly change from dative case to genitive:
> 
> "From the computer's perspective," ...
> 
> > + * a new frame it's done by "scanning out" the display image from top to
> > + * bottom, one row of pixels at a time. which row of pixels we're on is
> 
> s/which/Which
> 
> The text changes from third person (the computer) to first person
> (we're). Makes it harder to read. I'd remove both, "we" and "computer",
> and speak of display hardware or scanout engine.
> 
> > + * referred to as the scanline.
> 
> I'd say a scanline is any of them. Maybe say "current scanline"?
> 
> > + * Additionally, there's usually a couple of extra scanlines which we
> 
> "In addition to the display's visible area, there's usually a couple of
> extra scanlines that" ...
> 
> > + * scan out, but aren't actually displayed on the screen (these sometimes
> > + * get used by HDMI audio and friends, but that's another story).
> > + * The period where we're on these scanlines is referred to as the vblank.
> 
> I'd replace vblank with "vertical blanking period." That term is
> required in the next paragraph.
> 
> The time when the hardware operates on these invisible scanlines is
> referred to as vertical blanking period, or simply vblank.
> 
> > + *
> > + * On a lot of display hardware, programming needs to take effect during the
> > + * vertical blanking period so that settings like gamma, what frame we're
> 
> "we" again
> 
> > + * scanning out, etc. can be safely changed without showing visual tearing
> > + * on the screen. In some unforgiving hardware, some of this programming has
> > + * to both start and end in the same vblank - 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
> > 
> 
> In any case
> 
> Acked-by: Thomas Zimmermann <tzimmermann@suse.de>

Thanks for the detailed feedabck - I have tried to reword it so it
better fits the context and have taking into account your suggetions.
See other mail for the updated patch.

	Sam
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