linux-kernel - Re: [PATCH 0/5] drm/sun4i: Handle TV overscan

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Date:   Mon, 7 Nov 2016 15:11:46 +0100
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Sean Paul <seanpaul@...omium.org>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        DRI mailing list <dri-devel@...ts.freedesktop.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Linux ARM Kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 0/5] drm/sun4i: Handle TV overscan

Hi Sean,

On Thu, Nov 03, 2016 at 03:11:26PM -0600, Sean Paul wrote:
> On Thu, Nov 3, 2016 at 3:01 AM, Maxime Ripard
> <maxime.ripard@...e-electrons.com> wrote:
> > Hi Russell,
> >
> > On Mon, Oct 31, 2016 at 08:42:34AM +0000, Russell King - ARM Linux wrote:
> >> On Tue, Oct 18, 2016 at 12:03:49PM +0200, Maxime Ripard wrote:
> >> > 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.

Yes, the first one is pretty scary.

If it can ease your review, I made a bunch of unittests to test that
code. It's pretty hacky (basically a copy of some kernel structures
and the new logic to parse the command line), but it should test it
with a significant number of cases:

http://code.bulix.org/4lnlk7-107122?raw

It's pretty straightforward to compile, you just have to link against
cmocka.

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

I'll reply to his mail.

Thanks!
Maxime

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

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