linux-kernel - Re: [PATCH v10 0/2] Panel rotation patches

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Date:   Wed, 15 Apr 2020 00:18:22 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     "dbasehore ." <dbasehore@...omium.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        Sean Paul <sean@...rly.run>
Subject: Re: [PATCH v10 0/2] Panel rotation patches

14.04.2020 22:32, dbasehore . пишет:
> Hi Dmitry, sorry for the late reply.
> 
> On Sun, Mar 8, 2020 at 12:25 PM Dmitry Osipenko <digetx@...il.com> wrote:
>>
>> 06.03.2020 03:21, Derek Basehore пишет:
>>> 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 rotated
>> by 180° 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 DRM
>> core currently doesn't support use-case where scan-out needs to rotated
>> 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?

AFAIK, things like Xorg modesetting don't support that orientation property.