[libcamera-devel] [RFC PATCH 2/2] libcamera: camera_sensor: Do not clear camera flips when listing formats

[Dave Stevenson]

On Thu, 3 Nov 2022 at 11:24, David Plowman
<david.plowman at raspberrypi.com> wrote:
>
> Hi Dave
>
> On Thu, 3 Nov 2022 at 11:02, Dave Stevenson
> <dave.stevenson at raspberrypi.com> wrote:
> >
> > Hi David
> >
> > On Thu, 3 Nov 2022 at 10:40, David Plowman via libcamera-devel
> > <libcamera-devel at lists.libcamera.org> wrote:
> > >
> > > Previously the code used to clear the camnera's h and v flip bits when
> > > enumerating the supported formats so as to obtain any Bayer formats in
> > > the sensor's native (untransformed) orientation. However this fails
> > > when the camera is already in use elsewhere.
> > >
> > > Instead, we query the current state of the flip bits and transform the
> > > formats - which we obtain in their flipped orientation - back into
> > > their native orientation to be stored.
> >
> > I don't believe that libcamera knows for definite whether the sensor
> > changes the Bayer order or not. Several of the OnSemi sensors I have
> > seen do not change, presumably as they shift their crop by 1 pixel.
>
> Yes, that's a good point. I've vaguely assumed that I can check the
> control's V4L2_CTRL_FLAG_MODIFY_LAYOUT to discover whether this is the
> case or not, but as we keep on discovering, there may be no guarantees
> about this. Do we know what these particular sensors do here? The Pi
> PH actually already assumes this flag "works", so the changes here
> possibly don't make anything worse, though they do engrain the
> assumption more deeply...

Yes I believe V4L2_CTRL_FLAG_MODIFY_LAYOUT should do what you want.

The OnSemi sensors I'm thinking of don't have drivers in mainline, so
there's no driver to check currently.

Looking at mainline, only imx219 and imx258 set the flag.
- ov2680, imx208, imx319, imx355, mt9m001, ov08d10 all change the
order but don't set V4L2_CTRL_FLAG_MODIFY_LAYOUT
- hi847 and ov13b10 move the crop to maintain the Bayer order.
- imx274 and ov5648 only ever report one order, but supports flips and
has no apparent cropping shift.
- I have missed it in my imx290 patches to add flips that I was about to send!

So, as Jacopo summarised the situation on event handlers for controls,
room for improvement!

  Dave

> Presumably you can rely on the formats being returned correctly after
> setting the flip bits, though having to re-query the formats from the
> device like that would be irritating too. And you'd never be able to
> predict the format ahead of time, only after setting it. I don't know
> if that's better or worse than saying "change the driver". Opinions
> welcome on that one!
>
> To be honest I always have difficulty with the Bayer order being part
> of the format. An application might legitimately want to have a say
> about the bit depth or packing, but the Bayer order?? Being able to
> request an XXXX ("anything goes") Bayer order, which gets updated once
> the sensor is configured, would be much more application-friendly. But
> another can of worms!!
>
> David
>
> >
> > The original comment mentioned that scenario:
> > "This is harmless for sensors where the flips don't affect the Bayer order"
> >
> >   Dave
> >
> > > Signed-off-by: David Plowman <david.plowman at raspberrypi.com>
> > > ---
> > >  src/libcamera/camera_sensor.cpp | 51 +++++++++++++++++++++++++++------
> > >  1 file changed, 43 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/src/libcamera/camera_sensor.cpp b/src/libcamera/camera_sensor.cpp
> > > index 572a313a..6670dfb9 100644
> > > --- a/src/libcamera/camera_sensor.cpp
> > > +++ b/src/libcamera/camera_sensor.cpp
> > > @@ -19,6 +19,8 @@
> > >
> > >  #include <libcamera/base/utils.h>
> > >
> > > +#include <libcamera/transform.h>
> > > +
> > >  #include "libcamera/internal/bayer_format.h"
> > >  #include "libcamera/internal/camera_lens.h"
> > >  #include "libcamera/internal/camera_sensor_properties.h"
> > > @@ -108,18 +110,51 @@ int CameraSensor::init()
> > >                 return ret;
> > >
> > >         /*
> > > -        * Clear any flips to be sure we get the "native" Bayer order. This is
> > > -        * harmless for sensors where the flips don't affect the Bayer order.
> > > +        * We want to get the native mbus codes for the sensor, without any flips.
> > > +        * We can't clear any flips here, so we have to read the current values
> > > +        * (if the flip controls exist), decide whether they actually modify any
> > > +        * output Bayer pattern, and finally undo their effect on the formats.
> > > +        *
> > > +        * First, check if the flip controls exist and if so read them.
> > >          */
> > >         ControlList ctrls(subdev_->controls());
> > > -       if (subdev_->controls().find(V4L2_CID_HFLIP) != subdev_->controls().end())
> > > -               ctrls.set(V4L2_CID_HFLIP, 0);
> > > -       if (subdev_->controls().find(V4L2_CID_VFLIP) != subdev_->controls().end())
> > > -               ctrls.set(V4L2_CID_VFLIP, 0);
> > > -       subdev_->setControls(&ctrls);
> > > +       std::vector<uint32_t> flipCtrlIds;
> > > +       bool hasHflip = subdev_->controls().find(V4L2_CID_HFLIP) != subdev_->controls().end();
> > > +       bool hasVflip = subdev_->controls().find(V4L2_CID_VFLIP) != subdev_->controls().end();
> > > +       if (hasHflip)
> > > +               flipCtrlIds.push_back(V4L2_CID_HFLIP);
> > > +       if (hasVflip)
> > > +               flipCtrlIds.push_back(V4L2_CID_VFLIP);
> > > +       ControlList flipCtrls = subdev_->getControls(flipCtrlIds);
> > > +
> > > +       /* Now construct a transform that would undo any flips. */
> > > +       Transform transform = Transform::Identity;
> > > +       if (hasHflip && flipCtrls.get(V4L2_CID_HFLIP).get<int>()) {
> > > +               const struct v4l2_query_ext_ctrl *extCtrl = subdev_->controlInfo(V4L2_CID_HFLIP);
> > > +               if (extCtrl->flags & V4L2_CTRL_FLAG_MODIFY_LAYOUT)
> > > +                       transform |= Transform::HFlip;
> > > +       }
> > > +       if (hasVflip && flipCtrls.get(V4L2_CID_VFLIP).get<int>()) {
> > > +               const struct v4l2_query_ext_ctrl *extCtrl = subdev_->controlInfo(V4L2_CID_VFLIP);
> > > +               if (extCtrl->flags & V4L2_CTRL_FLAG_MODIFY_LAYOUT)
> > > +                       transform |= Transform::VFlip;
> > > +       }
> > > +
> > > +       /* Finally get the formats, and apply the transform to the mbus codes. */
> > > +       auto formats = subdev_->formats(pad_);
> > > +       for (const auto &format : formats) {
> > > +               unsigned int mbusCode = format.first;
> > > +               BayerFormat bayerFormat = BayerFormat::fromMbusCode(mbusCode);
> > > +               bool valid = true;
> > > +
> > > +               if (bayerFormat.isValid())
> > > +                       mbusCode = bayerFormat.transform(transform).toMbusCode(valid);
> > > +
> > > +               if (valid)
> > > +                       formats_[mbusCode] = std::move(format.second);
> > > +       }
> > >
> > >         /* Enumerate, sort and cache media bus codes and sizes. */
> > > -       formats_ = subdev_->formats(pad_);
> > >         if (formats_.empty()) {
> > >                 LOG(CameraSensor, Error) << "No image format found";
> > >                 return -EINVAL;
> > > --
> > > 2.30.2
> > >