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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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