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From:   "dbasehore ." <dbasehore@chromium.org>
Date:   Tue, 14 Apr 2020 14:32:24 -0700
Message-ID: <CAGAzgsrNrq+S+-5KEFVnJn6S5DRn1fKkToD5=KR911T9AOAF-w@mail.gmail.com>
Subject: Re: [PATCH v10 0/2] Panel rotation patches
To:     Dmitry Osipenko <digetx@gmail.com>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Sam Ravnborg <sam@ravnborg.org>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
        Sean Paul <sean@poorly.run>
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On Tue, Apr 14, 2020 at 2:18 PM Dmitry Osipenko <digetx@gmail.com> wrote:
>
> 14.04.2020 22:32, dbasehore . =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
> > Hi Dmitry, sorry for the late reply.
> >
> > On Sun, Mar 8, 2020 at 12:25 PM Dmitry Osipenko <digetx@gmail.com> wrot=
e:
> >>
> >> 06.03.2020 03:21, Derek Basehore =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
> >>> This adds the plumbing for reading panel rotation from the devicetree
> >>> and sets up adding a panel property for the panel orientation on
> >>> Mediatek SoCs when a rotation is present.
> >>
> >> Hello Derek and everyone,
> >>
> >> I'm looking at adding display rotation support to NVIDIA Tegra DRM
> >> driver because some devices have display panel physically mounted
> >> upside-down, and thus, display controller's scan-out needs to be rotat=
ed
> >> by 180=C2=B0 in this case.
> >>
> >> Derek, yours panel-rotation patches add support for assigning panel's
> >> orientation to the connector, but then only primary display plane
> >> receives rotation value in [1], while rotation needs to be applied to
> >> all available overlay/cursor planes and this should happen in other
> >> places than [1] as well.
> >
> > This is intended. We don't correct the output in the kernel. We
> > instead rely on notifying userspace that the panel is rotated, then we
> > handle it there.
> >
> >>
> >> [1] drm_client_modeset_commit_atomic()
> >>
> >> Please also note that in a case of the scan-out rotation, plane's
> >> coordinates need to be changed in accordance to the display's rotation=
.
> >>
> >> I looked briefly through the DRM code and my understanding that the DR=
M
> >> core currently doesn't support use-case where scan-out needs to rotate=
d
> >> based on a panel's orientation, correct? Is it the use-case you're
> >> working on for the Mediatek driver?
> >
> > Yes, we rely on userspace to rotate the output. The major reason for
> > this is because there may not be a "free" hardware rotation that can
> > be applied to the overlay. Sean Paul and others also preferred that
> > userspace control what is output to the screen instead of the kernel
> > taking care of it. This code just adds the drm property to the panel.
> >
>
> Could you please explain what that userspace is?

This was added for Chrome OS, which uses its own graphics stack,
Ozone, instead of Xorg.

>
> AFAIK, things like Xorg modesetting don't support that orientation proper=
ty.