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

On 7/23/25 11:44, Jacopo Mondi wrote:

On Wed, Jul 23, 2025 at 11:29:27AM +0200, Fabian Pfitzner wrote:

quoted

On 7/23/25 11:17, Jacopo Mondi wrote:

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Hi Fabian

On Wed, Jul 23, 2025 at 10:58:28AM +0200, Fabian Pfitzner wrote:

quoted

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

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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 <redacted>
---
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 [off-list ref]

--
Pengutronix e.K.                           | Fabian Pfitzner             |
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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    |