[PATCH 0/5] drm/sun4i: Handle TV overscan

On Thu, Nov 3, 2016 at 3:01 AM, Maxime Ripard
[off-list ref] wrote:

Hi Russell,

On Mon, Oct 31, 2016 at 08:42:34AM +0000, Russell King - ARM Linux wrote:

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On Tue, Oct 18, 2016 at 12:03:49PM +0200, Maxime Ripard wrote:

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The first one is that this overscanning should be reported by the
connector I guess? but this is really TV specific, so we need one way
to let the user tell how the image is displayed on its side, and we
cannot really autodetect it, and this needs to be done at runtime so
that we can present some shiny interface to let it select which
overscan ratio works for him/her.

See xbmc... they go through a nice shiny setup which includes adjusting
the visible area.  From what I remember, it has pointers on each corner
which you can adjust to be just visible on the screen, so xbmc knows
how much overscan there is, and xbmc itself reduces down to the user
set size.

Yes. And that is an XBMC only solution, that doesn't work with the
fbdev emulation and is probably doing an additional composition to
scale down and center their frames through OpenGL.

We might not have a GPU in the system, and we might not even have an
entire graphic stack on top either, so I don't think fixing at the
user-space level is a good option (especially since we already have an
overscan property in DRM).

Hi Maxime,
I took a quick look at the first 2 patches in the series and they look
good at first glance. I have them in my queue to review more
carefully.

Can you explain why you can't fix this by specifying a new mode with
big porches (as Russell suggested)?

Sean

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The second one is that we still need to expose the reduced modes to
userspace, and not only the displayed size, so that the applications
know what they must draw on. But I guess this could be adjusted by the
core too.

In order to work consistently, I think all planes should be adjusted
that way, so that relative coordinates are from the primary plane
origin, and not the display origin. But that could be adjusted too by
the core I guess.

I'm not sure about that - we want the graphics to be visible, but that
may not be appropriate for an video overlay frame.  It's quite common
for (eg) broadcast video to contain dead pixels or other artifacts on
the right hand side, and the broadcast video expects overscan to be
present.

I know this because I have run my TV with overscan disabled, even for
broadcast TV.

I know, but on this particular hardware, composite really is just
another video output. There's not even a TV receiver in it, so I don't
think we have to worry about it.

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The fourth one being the major one. Every time I raised the issue on
IRC, the answer basically was "we don't care about analog", so I'm a
bit pessimistic about whether dealing with this in the core would be
accepted, hence why I chose to deal with this at the driver level.

Yea, that's quite sad, "analog" has become a dirty word, but really
this has nothing to do with "analog" at all - there are LCD TVs (and
some monitors) out there which take HDMI signals but refuse to
disable overscan no matter what you do to them if you provide them
with a "broadcast"  mode - so the analog excuse is very poor.

I'd agree with you, but I was also told to not turn that into a
generic code and deal with that in my driver.

Do you have any suggestions?

Thanks,
Maxime

--
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com