<Snip>
>
> struct v4l2_format {
> enum v4l2_buf_type type;
> union {
> struct v4l2_pix_format pix; /*
>V4L2_BUF_TYPE_VIDEO_CAPTURE */
>+ struct v4l2_pix_format_mplane pix_mp; /*
>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE */
> struct v4l2_window win; /*
>V4L2_BUF_TYPE_VIDEO_OVERLAY */
> struct v4l2_vbi_format vbi; /*
>V4L2_BUF_TYPE_VBI_CAPTURE */
> struct v4l2_sliced_vbi_format sliced; /*
>V4L2_BUF_TYPE_SLICED_VBI_CAPTURE */
> __u8 raw_data[200]; /* user-defined */
> } fmt;
> };
>
>For the new buffer types mp_pix member is chosen. For those buffer types,
>struct v4l2_pix_format_mplane is used:
>
Typo. replae mp_pix with pix_mp
>/**
> * struct v4l2_pix_format_mplane - multiplanar format definition
> * @width: image width in pixels
> * @height: image height in pixels
> * @pixelformat: little endian four character code (fourcc)
> * @field: field order (for interlaced video)
> * @colorspace: supplemental to pixelformat
> * @plane_fmt: per-plane information
> * @num_planes: number of planes for this format and number of
>valid
<Snip>
>
>
>7. Format conversion
>----------------------------------
>v4l2 core ioctl handling includes a simple conversion layer that allows
>translation - when possible - between multi-planar and single-planar APIs,
>transparently to drivers and applications.
>
>The table below summarizes conversion behavior for cases when driver and
>application use different API versions:
>
>---------------------------------------------------------------
> | Application MP --> Driver SP --> Application MP
> G_FMT | always OK | always OK
> S_FMT | -EINVAL | always OK
> TRY_FMT | -EINVAL | always OK
>---------------------------------------------------------------
> | Application SP --> Driver MP --> Application SP
> G_FMT | always OK | -EBUSY
> S_FMT | always OK | -EBUSY and WARN()
> TRY_FMT | always OK | -EBUSY and WARN()
>
What is the logic behind using -EBUSY for this? Why not -EINVAL? Also why use WARN()?
>Legend:
>- SP - single-planar API used (NOT format!)
>- MP - multi-planar API used (NOT format!)
>- always OK - conversion is always valid irrespective of number of planes
>- -EINVAL - if an MP application tries to TRY or SET a format with more
> than 1 plane, EINVAL is returned from the conversion function
> (of course, 1-plane multi-planar formats work and are
>converted)
>- -EBUSY - if an MP driver returns a more than 1-plane format to an SP
> application, the conversion layer returns EBUSY to the
>application;
> this is useful in cases when the driver is currently set to a
>more
> than 1-plane format, SP application would not be able to
>understand
> it)
>- -EBUSY and WARN() - there is only one reason for which SET or TRY from an
>SP
> application would result in a driver returning a more than 1-
>plane
> format - when the driver adjusts a 1-plane format to a more than
> 1-plane format. This should not happen and is a bug in driver,
>hence
> a WARN_ON(). Application receives EBUSY.
>
>
Suppose, S_FMT/TRY_FMT is called with UYVY format and driver supports only NV12 (2 plane) only, then for
Application SP --> Driver MP --> Application SP
I guess in this case, new drivers that supports multi-plane format would have to return old NV12 format code (for backward compatibility). Is
this handled by driver or translation layer?
Application MP --> Driver SP --> Application MP
In this case, new driver would return new NV12 format code and have no issue.
Not sure what translation layer does in this scenario.
<snip>
>
>===============================================
>V. Using ioctl()s and mmap()
>===============================================
>
>* Format calls (VIDIOC_S/TRY/G_FMT) are converted transparently across APIs
> by the ioctl handling code, where possible. Conversion from single-planar
> to multi-planar cannot fail, but the other way around is possible only
>for
> 1-plane formats.
> Possible errors in conversion are described below.
>
Could you explain what you mean by conversion of formats? The idea of the translation layer functionality is not clear to me. An example would help.
Murali
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