On Mon, 2017-03-20 at 12:08 +0000, Russell King - ARM Linux wrote:

On Mon, Mar 20, 2017 at 12:55:26PM +0100, Philipp Zabel wrote:

quoted

The above paragraph suggests we skip any rectangles that are not
supported. In our case that would be 3. and 4., since the CSI can't
compose into a larger frame. I hadn't realised that the crop selection
currently happens on the source pad.

I'd recommend viewing the documentation in its post-processed version,
because then you get the examples as pictures, and they say that a
picture is worth 1000 words.  See

  https://linuxtv.org/downloads/v4l-dvb-apis/uapi/v4l/dev-subdev.html

There is almost an exact example of what we're trying to do - it's
figure 4.6.  Here, we have a sink pad with a cropping rectangle on
the input, which is then scaled to a composition rectangle (there's
no bounds rectangle, and it's specified that in such a case the
top,left of the composition rectangle will always be 0,0 - see quote
below).

Where it differs is that the example also supports source cropping
for two source pads.  We don't support that.

The same document says:

  Scaling support is optional. When supported by a subdev, the crop
  rectangle on the subdev's sink pad is scaled to the size configured
  using the
  :ref:`VIDIOC_SUBDEV_S_SELECTION <VIDIOC_SUBDEV_G_SELECTION>` IOCTL
  using ``V4L2_SEL_TGT_COMPOSE`` selection target on the same pad. If the
  subdev supports scaling but not composing, the top and left values are
  not used and must always be set to zero.

Right, this sentence does imply that when scaling is supported, there
must be a sink compose rectangle, even when composing is not.

I have previously set up scaling like this:

media-ctl --set-v4l2 "'ipu1_csi0_mux':2[fmt:UYVY2X8/1920x1080@1/60]"
media-ctl --set-v4l2 "'ipu1_csi0':2[fmt:AYUV32/960x540@1/30]"

Does this mean, it should work like this instead?

media-ctl --set-v4l2 "'ipu1_csi0_mux':2[fmt:UYVY2X8/1920x1080@1/60]"
media-ctl --set-v4l2 "'ipu1_csi0':0[fmt:UYVY2X8/1920x1080@1/60,compose:(0,0)/960x540]"
media-ctl --set-v4l2 "'ipu1_csi0':2[fmt:AYUV32/960x540@1/30]"

I suppose setting the source pad format should not be allowed to modify
the sink compose rectangle.

regards
Philipp