It is the vfrontporch of field 1 that is one half-line longer,
not the backporch.
The order of the vertical signals in an interlaced system is:
Field 1:
vsync
vbackporch
active video of field 1
vfrontporch + 0.5
Field 2:
il_vsync
il_vbackporch - 0.5
active video of field 2
il_vfrontporch
Interlaced systems that use HALF_LINE set the il_ fields as follows:
il_vfrontporch = vfrontporch
il_vsync = vsync
il_vbackporch = vbackporch + 1
So the total vertical blanking for field 1 is:
vsync + vbackporch + vfrontporch + 0.5
and for field 2:
vsync + vbackporch + 1 + vfrontporch - 0.5 ==
vsync + vbackporch + vfrontporch + 0.5
So each field has the same number of half-lines.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
---
diff --git a/Documentation/media/uapi/v4l/vidioc-g-dv-timings.rst b/Documentation/media/uapi/v4l/vidioc-g-dv-timings.rst
index 5712bd48e687..5c675cbac4cf 100644
--- a/Documentation/media/uapi/v4l/vidioc-g-dv-timings.rst
+++ b/Documentation/media/uapi/v4l/vidioc-g-dv-timings.rst
@@ -279,7 +279,7 @@ EBUSY
then it will set this flag to signal this to the application.
* - ``V4L2_DV_FL_HALF_LINE``
- Specific to interlaced formats: if set, then the vertical
- backporch of field 1 (aka the odd field) is really one half-line
+ frontporch of field 1 (aka the odd field) is really one half-line
longer and the vertical backporch of field 2 (aka the even field)
is really one half-line shorter, so each field has exactly the
same number of half-lines. Whether half-lines can be detected or
