Re: [PATCH 0/2] parse horizontal/vertical flip properties

[Fabian Pfitzner <f.pfitzner@pengutronix.de>]

On 7/23/25 11:44, Jacopo Mondi wrote:
> On Wed, Jul 23, 2025 at 11:29:27AM +0200, Fabian Pfitzner wrote:
>> On 7/23/25 11:17, Jacopo Mondi wrote:
>>> Hi Fabian
>>>
>>> On Wed, Jul 23, 2025 at 10:58:28AM +0200, Fabian Pfitzner wrote:
>>>> There are cameras containing a mirror on their optical path e. g. when
>>>> mounted upside down.
>>> How is this different from 'rotation = 180' ?
>> If you simply want to flip the output (e. g. horizontally), you cannot do
>> this with a rotation.
>> The camera I'm referring to is not only upside down, but also flipped
>> horizontally.
> 180 degress rotation = HFLIP + VFLIP
I do not want to do both. Only one of them.
>
> Yes, you can't express 'mirror' in DTS, because DTS are about the
> physical mounting rotation of the camera. Sensor drivers shall not
> apply any flip control automatically, it's userspace that by parsing
> the rotation property through the associated v4l2 controls should decide
> if it has to apply flips or not to correct the images.
>
> What is the use case you had in mind ? Tell the driver through a DTS
> property it has to apply flips to auto-compensate ? Because I think we
> shouldn't and if I'm not mistaken we also document it:
> https://www.kernel.org/doc/html/latest/userspace-api/media/drivers/camera-sensor.html#rotation-orientation-and-flipping
I have a camera that does a horizontal flip in its hardware, so the 
output is not what I want. My example above was misleading. The rotation 
fixes the "upside down" problem, but does not fix the flip.

Doing that in userspace might be a solution, but in my opinion it is a 
bit ugly to write a script that always sets the flip property from 
userspace when the device was started.
A much cleaner way would be to simply set this property in the device 
tree such that the driver can be initially configured with the proper 
values.

PS: I have to send this email twice. The first one contained HTML parts 
that were rejected by some receivers...

>
> TL;DR drivers shall not flip, userspace should. Mirroring is an effect
> of drivers applying an HFLIP, because unless I'm missing something
> obvious, 'mirror' is not a physical mounting configuration of the camera
> sensor.
>
> FIY we're talking about something similar in libcamera
> https://lists.libcamera.org/pipermail/libcamera-devel/2025-July/051533.html
>
>>>> Introduce two options to change the device's flip property via device tree.
>>>>
>>>> As there is already support for the panel-common driver [1], add it for cameras in the same way.
>>>>
>>>> [1] commit 3c0ecd83eee9 ("dt-bindings: display: panel: Move flip properties to panel-common")
>>>>
>>>> Signed-off-by: Fabian Pfitzner <f.pfitzner@pengutronix.de>
>>>> ---
>>>> Fabian Pfitzner (2):
>>>>         media: dt-bindings: add flip properties
>>>>         media: v4l: fwnode: parse horizontal/vertical flip properties
>>>>
>>>>    .../devicetree/bindings/media/video-interface-devices.yaml        | 8 ++++++++
>>>>    drivers/media/v4l2-core/v4l2-fwnode.c                             | 3 +++
>>>>    include/media/v4l2-fwnode.h                                       | 4 ++++
>>>>    3 files changed, 15 insertions(+)
>>>> ---
>>>> base-commit: 6832a9317eee280117cd695fa885b2b7a7a38daf
>>>> change-id: 20250718-fpf-media-dt-flip-7fcad30bcfb7
>>>>
>>>> Best regards,
>>>> --
>>>> Fabian Pfitzner <f.pfitzner@pengutronix.de>
>>>>
>> --
>> Pengutronix e.K.                           | Fabian Pfitzner             |
>> Steuerwalder Str. 21                       | https://www.pengutronix.de/ |
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>>
-- 
Pengutronix e.K.                           | Fabian Pfitzner             |
Steuerwalder Str. 21                       | https://www.pengutronix.de/ |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-9    |