On Mon July 30 2012 21:06:33 Laurent Pinchart wrote:
> Hi Hans,
>
> On Monday 30 July 2012 20:36:36 Hans Verkuil wrote:
> > On Sat July 28 2012 00:01:24 Sakari Ailus wrote:
> > > On Fri, Jul 27, 2012 at 04:25:04PM +0530, Prabhakar Lad wrote:
> > > > From: Manjunath Hadli <manjunath.ha...@ti.com>
> > > >
> > > > add new enum entries for supporting the media-bus formats on dm365.
> > > > These include some bayer and some non-bayer formats.
> > > > V4L2_MBUS_FMT_YDYUYDYV8_1X16 and V4L2_MBUS_FMT_UV8_1X8 are used
> > > > internal to the hardware by the resizer.
> > > > V4L2_MBUS_FMT_SBGGR10_ALAW8_1X8 represents the bayer ALAW format
> > > > that is supported by dm365 hardware.
> > > >
> > > > Acked-by: Laurent Pinchart <laurent.pinch...@ideasonboard.com>
> > > > Acked-by: Hans Verkuil <hans.verk...@cisco.com>
> > > > Signed-off-by: Manjunath Hadli <manjunath.ha...@ti.com>
> > > > Signed-off-by: Lad, Prabhakar <prabhakar....@ti.com>
> > > > Cc: Sakari Ailus <sakari.ai...@iki.fi>
> > > > Cc: Guennadi Liakhovetski <g.liakhovet...@gmx.de>
> > > > ---
> > > >
> > > > Documentation/DocBook/media/v4l/subdev-formats.xml | 250
> > > > +++++++++++++++++++- include/linux/v4l2-mediabus.h
> > > > | 10 +-
> > > > 2 files changed, 252 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/Documentation/DocBook/media/v4l/subdev-formats.xml
> > > > b/Documentation/DocBook/media/v4l/subdev-formats.xml index
> > > > 49c532e..75dc275 100644
> > > > --- a/Documentation/DocBook/media/v4l/subdev-formats.xml
> > > > +++ b/Documentation/DocBook/media/v4l/subdev-formats.xml
> > > > @@ -353,9 +353,9 @@
> > > >
> > > > <listitem><para>The number of bits per pixel component. All
> components
> > > > are
> > > > transferred on the same number of bits. Common values are 8, 10
> > > > and
> > > > 12.</para> </listitem>
> > > >
> > > > - <listitem><para>If the pixel components are DPCM-compressed, a
> mention
> > > > of the - DPCM compression and the number of bits per compressed
> > > > pixel
> > > > component.</para> - </listitem>
> > > > + <listitem><para>The compression (optional). If the pixel
> > > > components
> > > > are
> > > > + ALAW- or DPCM-compressed, a mention of the compression scheme
> > > > and the
> > > > + number of bits per compressed pixel component.</para></listitem>
> > > >
> > > > <listitem><para>The number of bus samples per pixel. Pixels
> > > > that are
> > > > wider than the bus width must be transferred in multiple
> > > > samples.
> > > > Common values are 1 and 2.</para></listitem>
> > > >
> > > > @@ -504,6 +504,74 @@
> > > >
> > > > <entry>r<subscript>1</subscript></entry>
> > > > <entry>r<subscript>0</subscript></entry>
> > > >
> > > > </row>
> > > >
> > > > + <row id="V4L2-MBUS-FMT-SBGGR10-ALAW8-1X8">
> > > > + <entry>V4L2_MBUS_FMT_SBGGR10_ALAW8_1X8</entry>
> > > > + <entry>0x3015</entry>
> > > > + <entry></entry>
> > > > + <entry>-</entry>
> > > > + <entry>-</entry>
> > > > + <entry>-</entry>
> > > > + <entry>-</entry>
> > > > + <entry>b<subscript>7</subscript></entry>
> > > > + <entry>b<subscript>6</subscript></entry>
> > > > + <entry>b<subscript>5</subscript></entry>
> > > > + <entry>b<subscript>4</subscript></entry>
> > > > + <entry>b<subscript>3</subscript></entry>
> > > > + <entry>b<subscript>2</subscript></entry>
> > > > + <entry>b<subscript>1</subscript></entry>
> > > > + <entry>b<subscript>0</subscript></entry>
> > > > + </row>
> > > > + <row id="V4L2-MBUS-FMT-SGBRG10-ALAW8-1X8">
> > > > + <entry>V4L2_MBUS_FMT_SGBRG10_ALAW8_1X8</entry>
> > > > + <entry>0x3016</entry>
> > > > + <entry></entry>
> > > > + <entry>-</entry>
> > > > + <entry>-</entry>
> > > > + <entry>-</entry>
> > > > + <entry>-</entry>
> > > > + <entry>g<subscript>7</subscript></entry>
> > > > + <entry>g<subscript>6</subscript></entry>
> > > > + <entry>g<subscript>5</subscript></entry>
> > > > + <entry>g<subscript>4</subscript></entry>
> > > > + <entry>g<subscript>3</subscript></entry>
> > > > + <entry>g<subscript>2</subscript></entry>
> > > > + <entry>g<subscript>1</subscript></entry>
> > > > + <entry>g<subscript>0</subscript></entry>
> > > > + </row>
> > > > + <row id="V4L2-MBUS-FMT-SGRBG10-ALAW8-1X8">
> > > > + <entry>V4L2_MBUS_FMT_SGRBG10_ALAW8_1X8</entry>
> > > > + <entry>0x3017</entry>
> > > > + <entry></entry>
> > > > + <entry>-</entry>
> > > > + <entry>-</entry>
> > > > + <entry>-</entry>
> > > > + <entry>-</entry>
> > > > + <entry>g<subscript>7</subscript></entry>
> > > > + <entry>g<subscript>6</subscript></entry>
> > > > + <entry>g<subscript>5</subscript></entry>
> > > > + <entry>g<subscript>4</subscript></entry>
> > > > + <entry>g<subscript>3</subscript></entry>
> > > > + <entry>g<subscript>2</subscript></entry>
> > > > + <entry>g<subscript>1</subscript></entry>
> > > > + <entry>g<subscript>0</subscript></entry>
> > > > + </row>
> > > > + <row id="V4L2-MBUS-FMT-SRGGB10-ALAW8-1X8">
> > > > + <entry>V4L2_MBUS_FMT_SRGGB10_ALAW8_1X8</entry>
> > > > + <entry>0x3018</entry>
> > > > + <entry></entry>
> > > > + <entry>-</entry>
> > > > + <entry>-</entry>
> > > > + <entry>-</entry>
> > > > + <entry>-</entry>
> > > > + <entry>r<subscript>7</subscript></entry>
> > > > + <entry>r<subscript>6</subscript></entry>
> > > > + <entry>r<subscript>5</subscript></entry>
> > > > + <entry>r<subscript>4</subscript></entry>
> > > > + <entry>r<subscript>3</subscript></entry>
> > > > + <entry>r<subscript>2</subscript></entry>
> > > > + <entry>r<subscript>1</subscript></entry>
> > > > + <entry>r<subscript>0</subscript></entry>
> > > > + </row>
> > > >
> > > > <row id="V4L2-MBUS-FMT-SBGGR10-DPCM8-1X8">
> > > >
> > > > <entry>V4L2_MBUS_FMT_SBGGR10_DPCM8_1X8</entry>
> > > > <entry>0x300b</entry>
> > > >
> > > > @@ -853,10 +921,16 @@
> > > >
> > > > <title>Packed YUV Formats</title>
> > > >
> > > > <para>Those data formats transfer pixel data as (possibly
> > > > downsampled) Y, U
> > > >
> > > > - and V components. The format code is made of the following
> > > > information. + and V components. Some formats include dummy bits
> > > > in some of their samples + and are collectively referred to as
> > > > "YDYC" (Y-Dummy-Y-Chroma) formats. + One cannot rely on the values
> > > > of these dummy bits as those are undefined. + </para>
> > > > + <para>The format code is made of the following information.
> > > >
> > > > <itemizedlist>
> > > >
> > > > <listitem><para>The Y, U and V components order code, as
> > > > transferred
> > > > on the
> > > >
> > > > - bus. Possible values are YUYV, UYVY, YVYU and
> > > > VYUY.</para></listitem>
> > > > + bus. Possible values are YUYV, UYVY, YVYU and VYUY for formats
> > > > with
> no
> > > > + dummy bit, and YDYUYDYV, YDYVYDYU, YUYDYVYD and YVYDYUYD for
> > > > YDYC
> > > > formats. + </para></listitem>
> > > >
> > > > <listitem><para>The number of bits per pixel component. All
> components
> > > > are
> > > > transferred on the same number of bits. Common values are 8, 10
> > > > and
> > > > 12.</para> </listitem>
> > >
> > > I dicussed dummy vs. padding (zeros) with Laurent and we concluded we
> > > should use zero padding instead. The difference is that when processing
> > > the pixels no extra operations are necessary to get rid of the dummy data
> > > when the dummy bits are actually zero --- which in practice always is the
> > > case.
> > >
> > > I'm not aware of hardware that would assign padding bits (in this very
> > > purpose) that are a part of writes the width of bus width something else
> > > than zeros. It wouldn't make much sense either.
> > >
> > > So I suggest that dummy is replaced by padding which is defined to be
> > > zero.
> > >
> > > The letter in the format name could be 'Z', for example.
> > >
> > > Hans: what do you think?
> >
> > Bad idea. First of all, some hardware or FPGA can insert different values
> > there. It's something that Cisco uses in some cases: it makes it easier to
> > identify the dummy values if they have a non-zero fixed value.
> >
> > Another reason for not doing this is when such formats are used to display
> > video: you don't want to force the software to fill in the dummy values
> > with a specific value for no good reason. That would only cost extra CPU
> > cycles.
>
> On the other hand, when you process data that includes dummy bits stored in
> memory, knowing that the dummy bits are zero can save a mask operation.
>
> I don't have a strong opinion whether we should use zero or dummy bits for
> media bus formats. For memory formats I'd be inclined to use zero bits (at
> least when capturing).
And make a new pixel format if you have hardware that doesn't use zero? I think
it's overkill IMHO.
Regards,
Hans
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