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    SubjectRe: [PATCH v2] media/doc: Allow sizeimage to be set by v4l clients
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    Le mardi 14 mai 2019 à 10:54 +0200, Hans Verkuil a écrit :
    > Hi Stanimir,
    >
    > On 4/12/19 5:59 PM, Stanimir Varbanov wrote:
    > > This changes v4l2_pix_format and v4l2_plane_pix_format sizeimage
    > > field description to allow v4l clients to set bigger image size
    > > in case of variable length compressed data.
    >
    > I've been reconsidering this change. The sizeimage value in the format
    > is the minimum size a buffer should have in order to store the data of
    > an image of the width and height as described in the format.

    Should this read as the minimum size for the specific (returned by
    driver) width/height/bytesperline ?

    >
    > But there is nothing that prevents userspace from calling VIDIOC_CREATEBUFS
    > instead of VIDIOC_REQBUFS to allocate larger buffers.
    >
    > So do we really need this change?
    >
    > The more I think about this, the more uncomfortable I become with this change.
    >
    > Regards,
    >
    > Hans
    >
    > > Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
    > > ---
    > > Documentation/media/uapi/v4l/pixfmt-v4l2-mplane.rst | 13 ++++++++++++-
    > > Documentation/media/uapi/v4l/pixfmt-v4l2.rst | 11 ++++++++++-
    > > 2 files changed, 22 insertions(+), 2 deletions(-)
    > >
    > > diff --git a/Documentation/media/uapi/v4l/pixfmt-v4l2-mplane.rst b/Documentation/media/uapi/v4l/pixfmt-v4l2-mplane.rst
    > > index 5688c816e334..005428a8121e 100644
    > > --- a/Documentation/media/uapi/v4l/pixfmt-v4l2-mplane.rst
    > > +++ b/Documentation/media/uapi/v4l/pixfmt-v4l2-mplane.rst
    > > @@ -31,7 +31,18 @@ describing all planes of that format.
    > >
    > > * - __u32
    > > - ``sizeimage``
    > > - - Maximum size in bytes required for image data in this plane.
    > > + - Maximum size in bytes required for image data in this plane,
    > > + set by the driver. When the image consists of variable length
    > > + compressed data this is the number of bytes required by the
    > > + codec to support the worst-case compression scenario.
    > > +
    > > + For uncompressed images the driver will set the value. For
    > > + variable length compressed data clients are allowed to set
    > > + the sizeimage field, but the driver may ignore it and set the
    > > + value itself, or it may modify the provided value based on
    > > + alignment requirements or minimum/maximum size requirements.
    > > + If the client wants to leave this to the driver, then it should
    > > + set sizeimage to 0.
    > > * - __u32
    > > - ``bytesperline``
    > > - Distance in bytes between the leftmost pixels in two adjacent
    > > diff --git a/Documentation/media/uapi/v4l/pixfmt-v4l2.rst b/Documentation/media/uapi/v4l/pixfmt-v4l2.rst
    > > index 71eebfc6d853..0f7771151db9 100644
    > > --- a/Documentation/media/uapi/v4l/pixfmt-v4l2.rst
    > > +++ b/Documentation/media/uapi/v4l/pixfmt-v4l2.rst
    > > @@ -89,7 +89,16 @@ Single-planar format structure
    > > - Size in bytes of the buffer to hold a complete image, set by the
    > > driver. Usually this is ``bytesperline`` times ``height``. When
    > > the image consists of variable length compressed data this is the
    > > - maximum number of bytes required to hold an image.
    > > + number of bytes required by the codec to support the worst-case
    > > + compression scenario.
    > > +
    > > + For uncompressed images the driver will set the value. For
    > > + variable length compressed data clients are allowed to set
    > > + the sizeimage field, but the driver may ignore it and set the
    > > + value itself, or it may modify the provided value based on
    > > + alignment requirements or minimum/maximum size requirements.
    > > + If the client wants to leave this to the driver, then it should
    > > + set sizeimage to 0.
    > > * - __u32
    > > - ``colorspace``
    > > - Image colorspace, from enum :c:type:`v4l2_colorspace`.
    > >

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