Date:   Tue, 16 Jun 2020 20:20:57 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Emil Velikov <emil.l.velikov@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Derek Basehore <dbasehore@...omium.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Sean Paul <sean@...rly.run>, linux-tegra@...r.kernel.org,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v2 0/5] 180 degrees rotation support for NVIDIA Tegra DRM

16.06.2020 18:48, Emil Velikov пишет:
> On Tue, 16 Jun 2020 at 12:40, Dmitry Osipenko <digetx@...il.com> wrote:
>>
>> 16.06.2020 01:26, Emil Velikov пишет:
>>> Hi Dmitry,
>>>
>>> On Mon, 15 Jun 2020 at 08:28, Dmitry Osipenko <digetx@...il.com> wrote:
>>>>
>>>> Hello!
>>>>
>>>> This series adds 180° display plane rotation support to the NVIDIA Tegra
>>>> DRM driver which is needed for devices that have display panel physically
>>>> mounted upside-down, like Nexus 7 tablet device for example [1]. Since
>>>> DRM panel rotation is a new thing for a userspace, currently only
>>>> Opentegra Xorg driver handles the rotated display panel [2], but this
>>>> is good enough for the start.
>>>>
>>>> Note that later on it should be possible to implement a transparent 180°
>>>> display rotation for Tegra DRM driver which will remove the need to have
>>>> a bleeding edge userspace that knows how to rotate display planes and I'm
>>>> slowly working on it. For the starter we can go with the minimal rotation
>>>> support, so it's not a blocker.
>>>>
>>>> This series is based on the work that was made by Derek Basehore for the
>>>> Mediatek driver [3], his patch is included into this patchset. I added
>>>> my tested-by tag to the Derek's patch.
>>>>
>>>> Please review and apply, thanks in advance!
>>>>
>>>> [1] https://patchwork.ozlabs.org/project/linux-tegra/patch/20200607154327.18589-3-digetx@gmail.com/
>>>> [2] https://github.com/grate-driver/xf86-video-opentegra/commit/28eb20a3959bbe5bc3a3b67e55977093fd5114ca
>>>> [3] https://lkml.org/lkml/2020/3/5/1119
>>>>
>>>> Changelog:
>>>>
>>>> v2: - Dropped "drm/panel: Set display info in panel attach" patch, which
>>>>       turned out to be obsolete now.
>>>>
>>>>     - Renamed the cover-latter, hopefully this will fix the bouncing emails.
>>>>
>>>> Derek Basehore (1):
>>>>   drm/panel: Add helper for reading DT rotation
>>>>
>>>> Dmitry Osipenko (4):
>>>>   drm/panel: lvds: Set up panel orientation
>>>
>>> IMHO it's perfectly reasonable to report the panel orientation to
>>> userspace, which can apply plane rotation as needed.
>>>
>>> Although I see that this series, alike Derek's, has a couple of issues:
>>>  - only a single panel driver is updated
>>>  - rotation is _not_ listed as supported property, in said panel
>>> driver device-tree bindings
>>>
>>> My personal inclination is that we should aim for a comprehensive solution:
>>>  - wire all panel drivers, as currently documented (quick grep list below)
>>>  - document and wire-up the lvds and boe panels - as proposed by you
>>> and Derek respectively
>>>
>>> HTH
>>> Emil
>>>
>>> Documentation/devicetree/bindings/display/himax,hx8357d.txt:2
>>> Documentation/devicetree/bindings/display/ilitek,ili9225.txt:2
>>> Documentation/devicetree/bindings/display/ilitek,ili9341.txt:2
>>> Documentation/devicetree/bindings/display/ilitek,ili9486.yaml:2
>>> Documentation/devicetree/bindings/display/multi-inno,mi0283qt.txt:2
>>> Documentation/devicetree/bindings/display/panel/panel-common.yaml:2
>>> Documentation/devicetree/bindings/display/sitronix,st7586.txt:1
>>> Documentation/devicetree/bindings/display/sitronix,st7735r.yaml:2
>>
>> Rotation is a common DT panel property that is described in the
>> panel-common.yaml.
> The property was introduced almost exclusively for tiny drm panels.
> Those ones are a bit different from the rest (in panel/) -
> MIPI-DBI/SPI w/o (not connected at least) an actual GPU.
> 
> To make it a bit better, the rotation is seemingly performed in the
> tiny driver itself ouch.
> 
>> This property is supported by all panel bindings
>> because these bindings inherent the common properties from the
>> panel-common.yaml.
>>
> Seems like that was an unintentional change with the conversion to YAML.
> Beforehand only a few selected panels had rotation. Upon closer look -
> some panels do have follow-up fixes, to remove/limit the implicit
> inclusion.

Interesting.. my understanding that the rotation property is supposed to
be a generic property which represents physical orientation of a display
panel and hence it should be applicable to all panels.

> Sam seems like you've done most of the YAML conversion. IMHO it would
> make sense to revisit the patches and inherit common properties only
> as applicable.
> 
>> I don't think that it makes sense to wire up rotation property to all
>> panel drivers at once because those drivers will be untested, at least I
>> don't know anything about those other panels and can't test them. It
>> will be much better to support the rotation on by as-needed basis for
>> each panel driver individually.
> 
> How about CCing the author and reviewer asking them to test the patch?
> The only place where the patches might cause an issue is with tiny,
> although patches would still be appreciated.

There are quite a lot of panel drivers and I'm a bit doubtful that at
least half of devices that use those panels have any real use for the
rotation property. I could write the patches.. but in the end it could
be a wasted effort if nobody needs it, so I'd prefer not to do it.

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