Re: [PATCH] media: v4l2-subdev.h: allow V4L2_FRMIVAL_TYPE_CONTINUOUS & _STEPWISE

[Philippe De Muyter <phdm@macqel.be>]

Hi Hans,

On Tue, Aug 28, 2018 at 12:03:25PM +0200, Hans Verkuil wrote:
> Hi Philippe,
> 
> On 28/08/18 09:55, Philippe De Muyter wrote:
> > add max_interval and step_interval to struct
> > v4l2_subdev_frame_interval_enum.
> 
> Yeah, I never understood why this wasn't supported when this API was designed.
> Clearly an oversight.
> 
> > 
> > When filled correctly by the sensor driver, those fields must be
> > used as follows by the intermediate level :
> > 
> >         struct v4l2_frmivalenum *fival;
> >         struct v4l2_subdev_frame_interval_enum fie;
> > 
> >         if (fie.max_interval.numerator == 0) {
> >                 fival->type = V4L2_FRMIVAL_TYPE_DISCRETE;
> >                 fival->discrete = fie.interval;
> >         } else if (fie.step_interval.numerator == 0) {
> >                 fival->type = V4L2_FRMIVAL_TYPE_CONTINUOUS;
> >                 fival->stepwise.min = fie.interval;
> >                 fival->stepwise.max = fie.max_interval;
> >         } else {
> >                 fival->type = V4L2_FRMIVAL_TYPE_STEPWISE;
> >                 fival->stepwise.min = fie.interval;
> >                 fival->stepwise.max = fie.max_interval;
> >                 fival->stepwise.step = fie.step_interval;
> >         }
> 
> This is a bit too magical for my tastes. I'd add a type field:
> 
> #define V4L2_SUBDEV_FRMIVAL_TYPE_DISCRETE 0
> #define V4L2_SUBDEV_FRMIVAL_TYPE_CONTINUOUS 1
> #define V4L2_SUBDEV_FRMIVAL_TYPE_STEPWISE 2

Like that ?

	struct v4l2_subdev_frame_interval_enum {
		__u32 index;
		__u32 pad;
		__u32 code;
		__u32 width;
		__u32 height;
		struct v4l2_fract interval;
		__u32 which;
		__u32 type;
		struct v4l2_fract max_interval;
		struct v4l2_fract step_interval;
		__u32 reserved[3];
	};


> 
> Older applications that do not know about the type field will just
> see a single discrete interval containing the minimum interval.
> I guess that's OK as they will keep working.

That's actually what also happens with the above implementation, because
max_interval.numerator and step_interval.numerator were previously
reserved and thus 0, and if this code is moved to a helper function,
that does not matter if it's a little bit magical :).

Both implementations are equal to me, but the proposed one uses less
space from the 'reserved' field.

> 
> While at it: it would be really nice if you can also add stepwise
> support to VIDIOC_SUBDEV_ENUM_FRAME_SIZE. I think the only thing
> you need to do there is to add two new fields: step_width and step_height.
> If 0, then that just means a step size of 1.

I'll look at that if I find enough interest and test opportunity for it,
but those things are unrelated except that they are missing :)

> 
> Add some helper functions to translate between v4l2_subdev_frame_size/interval_enum
> and v4l2_frmsize/ivalenum and this becomes much cleaner.

OK

> 
> Regards,
> 
> 	Hans
> 
> > 
> > Signed-off-by: Philippe De Muyter <phdm@macqel.be>
> > ---
> >  .../uapi/v4l/vidioc-subdev-enum-frame-interval.rst | 39 +++++++++++++++++++++-
> >  include/uapi/linux/v4l2-subdev.h                   |  4 ++-
> >  2 files changed, 41 insertions(+), 2 deletions(-)
> > 
> > diff --git a/Documentation/media/uapi/v4l/vidioc-subdev-enum-frame-interval.rst b/Documentation/media/uapi/v4l/vidioc-subdev-enum-frame-interval.rst
> > index 1bfe386..acc516e 100644
> > --- a/Documentation/media/uapi/v4l/vidioc-subdev-enum-frame-interval.rst
> > +++ b/Documentation/media/uapi/v4l/vidioc-subdev-enum-frame-interval.rst
> > @@ -51,6 +51,37 @@ EINVAL error code if one of the input fields is invalid. All frame
> >  intervals are enumerable by beginning at index zero and incrementing by
> >  one until ``EINVAL`` is returned.
> >  
> > +If the sub-device can work only at the fixed set of frame intervals,
> > +driver must enumerate them with increasing indexes, by only filling
> > +the ``interval`` field.  If the sub-device can work with a continuous
> > +range of frame intervals, driver must only return success for index 0
> > +and fill ``interval`` with the minimum interval, ``max_interval`` with
> > +the maximum interval, and ``step_interval`` with 0 or the step between
> > +the possible intervals.
> > +
> > +Callers are expected to use the returned information as follows :
> > +
> > +.. code-block:: c
> > +
> > +        struct v4l2_frmivalenum * fival;
> > +        struct v4l2_subdev_frame_interval_enum fie;
> > +
> > +        if (fie.max_interval.numerator == 0) {
> > +                fival->type = V4L2_FRMIVAL_TYPE_DISCRETE;
> > +                fival->discrete = fie.interval;
> > +        } else if (fie.step_interval.numerator == 0) {
> > +                fival->type = V4L2_FRMIVAL_TYPE_CONTINUOUS;
> > +                fival->stepwise.min = fie.interval;
> > +                fival->stepwise.max = fie.max_interval;
> > +        } else {
> > +                fival->type = V4L2_FRMIVAL_TYPE_STEPWISE;
> > +                fival->stepwise.min = fie.interval;
> > +                fival->stepwise.max = fie.max_interval;
> > +                fival->stepwise.step = fie.step_interval;
> > +        }
> > +
> > +.. code-block:: c
> > +
> >  Available frame intervals may depend on the current 'try' formats at
> >  other pads of the sub-device, as well as on the current active links.
> >  See :ref:`VIDIOC_SUBDEV_G_FMT` for more
> > @@ -92,8 +123,14 @@ multiple pads of the same sub-device is not defined.
> >        - ``which``
> >        - Frame intervals to be enumerated, from enum
> >  	:ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`.
> > +    * - struct :c:type:`v4l2_fract`
> > +      - ``max_interval``
> > +      - Maximum period, in seconds, between consecutive video frames, or 0.
> > +    * - struct :c:type:`v4l2_fract`
> > +      - ``step_interval``
> > +      - Frame interval step size, in seconds, or 0.
> >      * - __u32
> > -      - ``reserved``\ [8]
> > +      - ``reserved``\ [4]
> >        - Reserved for future extensions. Applications and drivers must set
> >  	the array to zero.
> >  
> > diff --git a/include/uapi/linux/v4l2-subdev.h b/include/uapi/linux/v4l2-subdev.h
> > index 03970ce..c944644 100644
> > --- a/include/uapi/linux/v4l2-subdev.h
> > +++ b/include/uapi/linux/v4l2-subdev.h
> > @@ -128,7 +128,9 @@ struct v4l2_subdev_frame_interval_enum {
> >  	__u32 height;
> >  	struct v4l2_fract interval;
> >  	__u32 which;
> > -	__u32 reserved[8];
> > +	struct v4l2_fract max_interval;
> > +	struct v4l2_fract step_interval;
> > +	__u32 reserved[4];
> >  };
> >  
> >  /**
> > 

-- 
Philippe De Muyter +32 2 6101532 Macq SA rue de l'Aeronef 2 B-1140 Bruxelles