linux-kernel - Re: [PATCH v2] media/doc: Allow sizeimage to be set by v4l clients

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Date:   Tue, 14 May 2019 08:19:34 -0400
From:   Nicolas Dufresne <nicolas@...fresne.ca>
To:     Hans Verkuil <hverkuil@...all.nl>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        linux-media@...r.kernel.org
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] media/doc: Allow sizeimage to be set by v4l clients

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@...aro.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`.
> >