[PATCH/RFC 0/1] v4l: Add support for binary controls

[PATCH/RFC 0/1] v4l: Add support for binary controls

[Kamil Debski]

Hello,

This patch introduces new type of v4l2 control - the binary control. It
will be useful for exchanging raw binary data between the user space and
the driver/hardware.

The patch is pretty small – basically it adds a new control type.

1.  Reasons to include this new type
- Some devices require data which are not part of the stream, but there
are necessary for the device to work e.g. coefficients for transformation
matrices.
- String control is not suitable as it suggests that the data is a null
terminated string. This might be important when printing debug information -
one might output strings as they are and binary data in hex.

2. How does the binary control work
The binary control has been based on the string control. The principle of
use is the same. It uses v4l2_ext_control structure to pass the pointer and
size of the data. It is left for the driver to call the copy_from_user/
copy_to_user function to copy the data.

3. About the patch
The patch is pretty small – it basically adds a new control type. 

Best wishes,
-- 
Kamil Debski
Linux Platform Group
Samsung Poland R&D Center

[PATCH/RFC 1/1] v4l: Add support for binary controls

[Kamil Debski]

This control provides means to exchange raw
binary data between the user space and the driver.

Signed-off-by: Kamil Debski <k.debski@samsung.com>
Reviewed-by: Kyungmin Park <kyungmin.park@samsung.com>
---
 Documentation/DocBook/v4l/compat.xml             |    9 ++++++++
 Documentation/DocBook/v4l/videodev2.h.xml        |    2 +
 Documentation/DocBook/v4l/vidioc-g-ext-ctrls.xml |    6 +++++
 Documentation/DocBook/v4l/vidioc-queryctrl.xml   |   23 ++++++++++++++++-----
 drivers/media/video/v4l2-common.c                |    2 +
 include/linux/videodev2.h                        |    2 +
 6 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/Documentation/DocBook/v4l/compat.xml b/Documentation/DocBook/v4l/compat.xml
index b9dbdf9..83b8b64 100644
--- a/Documentation/DocBook/v4l/compat.xml
+++ b/Documentation/DocBook/v4l/compat.xml
@@ -2333,6 +2333,15 @@ more information.</para>
       </orderedlist>
     </section>
    </section>
+    <section>
+      <title>V4L2 in Linux 2.6.35</title>
+      <orderedlist>
+	<listitem>
+	  <para>Added support for binary data controls via new type <constant>V4L2_CTRL_TYPE_BINARY</constant>.</para>
+	</listitem>
+      </orderedlist>
+    </section>
+   </section>
 
    <section id="other">
      <title>Relation of V4L2 to other Linux multimedia APIs</title>
diff --git a/Documentation/DocBook/v4l/videodev2.h.xml b/Documentation/DocBook/v4l/videodev2.h.xml
index 0683259..c552134 100644
--- a/Documentation/DocBook/v4l/videodev2.h.xml
+++ b/Documentation/DocBook/v4l/videodev2.h.xml
@@ -169,6 +169,7 @@ enum <link linkend="v4l2-ctrl-type">v4l2_ctrl_type</link> {
         V4L2_CTRL_TYPE_INTEGER64     = 5,
         V4L2_CTRL_TYPE_CTRL_CLASS    = 6,
         V4L2_CTRL_TYPE_STRING        = 7,
+        V4L2_CTRL_TYPE_BINARY        = 8,
 };
 
 enum <link linkend="v4l2-tuner-type">v4l2_tuner_type</link> {
@@ -913,6 +914,7 @@ struct <link linkend="v4l2-ext-control">v4l2_ext_control</link> {
                 __s32 value;
                 __s64 value64;
                 char *string;
+		unsigned char *blob;
         };
 } __attribute__ ((packed));
 
diff --git a/Documentation/DocBook/v4l/vidioc-g-ext-ctrls.xml b/Documentation/DocBook/v4l/vidioc-g-ext-ctrls.xml
index 3aa7f8f..ab4f1c9 100644
--- a/Documentation/DocBook/v4l/vidioc-g-ext-ctrls.xml
+++ b/Documentation/DocBook/v4l/vidioc-g-ext-ctrls.xml
@@ -170,6 +170,12 @@ applications must set the array to zero.</entry>
 	    <entry><structfield>string</structfield></entry>
 	    <entry>A pointer to a string.</entry>
 	  </row>
+	  <row>
+	    <entry></entry>
+	    <entry>unsigned char *</entry>
+	    <entry><structfield>blob</structfield></entry>
+	    <entry>A pointer to a blob.</entry>
+	  </row>
 	</tbody>
       </tgroup>
     </table>
diff --git a/Documentation/DocBook/v4l/vidioc-queryctrl.xml b/Documentation/DocBook/v4l/vidioc-queryctrl.xml
index 4876ff1..d1cd5ee 100644
--- a/Documentation/DocBook/v4l/vidioc-queryctrl.xml
+++ b/Documentation/DocBook/v4l/vidioc-queryctrl.xml
@@ -142,9 +142,10 @@ bound for <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls and the
 lowest valid index (always 0) for <constant>V4L2_CTRL_TYPE_MENU</constant> controls.
 For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the minimum value
 gives the minimum length of the string. This length <emphasis>does not include the terminating
-zero</emphasis>. It may not be valid for any other type of control, including
-<constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a
-signed value.</entry>
+zero</emphasis>. For <constant>V4L2_CTRL_TYPE_BINARY</constant> controls this value
+gives the minimum length of the binary data. It may not be valid for any other type of
+ control, including <constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that
+ this is a signed value.</entry>
 	  </row>
 	  <row>
 	    <entry>__s32</entry>
@@ -155,7 +156,8 @@ highest valid index for <constant>V4L2_CTRL_TYPE_MENU</constant>
 controls.
 For <constant>V4L2_CTRL_TYPE_STRING</constant> controls the maximum value
 gives the maximum length of the string. This length <emphasis>does not include the terminating
-zero</emphasis>. It may not be valid for any other type of control, including
+zero</emphasis>. For <constant>V4L2_CTRL_TYPE_BINARY</constant> controls this value
+gives the maximum length of the binary data. It may not be valid for any other type of control, including
 <constant>V4L2_CTRL_TYPE_INTEGER64</constant> controls. Note that this is a
 signed value.</entry>
 	  </row>
@@ -166,8 +168,8 @@ signed value.</entry>
 <constant>V4L2_CTRL_TYPE_INTEGER</constant> controls. For
 <constant>V4L2_CTRL_TYPE_STRING</constant> controls this field refers to
 the string length that has to be a multiple of this step size.
-It may not be valid for any other type of control, including
-<constant>V4L2_CTRL_TYPE_INTEGER64</constant>
+For <constant>V4L2_CTRL_TYPE_BINARY</constant> controls the size of the binary data has to be a multiple of this step size. It may not be valid for any other type of
+control, including <constant>V4L2_CTRL_TYPE_INTEGER64</constant>
 controls.</para><para>Generally drivers should not scale hardware
 control values. It may be necessary for example when the
 <structfield>name</structfield> or <structfield>id</structfield> imply
@@ -319,6 +321,15 @@ Which character encoding is used will depend on the string control itself and
 should be part of the control documentation.</entry>
 	  </row>
 	  <row>
+	    <entry><constant>V4L2_CTRL_TYPE_BINARY</constant></entry>
+	    <entry>&ge; 0</entry>
+	    <entry>&ge; 1</entry>
+	    <entry>&ge; 0</entry>
+	    <entry>The minimum and maximum of the binary data length. The step size
+means that the length must be (minimum + N * step) characters long for
+N &ge; 0. </entry>
+	  </row>
+	  <row>
 	    <entry><constant>V4L2_CTRL_TYPE_CTRL_CLASS</constant></entry>
 	    <entry>n/a</entry>
 	    <entry>n/a</entry>
diff --git a/drivers/media/video/v4l2-common.c b/drivers/media/video/v4l2-common.c
index 36b5cb8..cbd770e 100644
--- a/drivers/media/video/v4l2-common.c
+++ b/drivers/media/video/v4l2-common.c
@@ -158,6 +158,8 @@ int v4l2_ctrl_check(struct v4l2_ext_control *ctrl, struct v4l2_queryctrl *qctrl,
 		return -EBUSY;
 	if (qctrl->type == V4L2_CTRL_TYPE_STRING)
 		return 0;
+	if (qctrl->type == V4L2_CTRL_TYPE_BINARY)
+		return 0;
 	if (qctrl->type == V4L2_CTRL_TYPE_BUTTON ||
 	    qctrl->type == V4L2_CTRL_TYPE_INTEGER64 ||
 	    qctrl->type == V4L2_CTRL_TYPE_CTRL_CLASS)
diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
index 3793d16..5a62c9a 100644
--- a/include/linux/videodev2.h
+++ b/include/linux/videodev2.h
@@ -168,6 +168,7 @@ enum v4l2_ctrl_type {
 	V4L2_CTRL_TYPE_INTEGER64     = 5,
 	V4L2_CTRL_TYPE_CTRL_CLASS    = 6,
 	V4L2_CTRL_TYPE_STRING        = 7,
+	V4L2_CTRL_TYPE_BINARY        = 8,
 };
 
 enum v4l2_tuner_type {
@@ -918,6 +919,7 @@ struct v4l2_ext_control {
 		__s32 value;
 		__s64 value64;
 		char *string;
+		unsigned char *blob;
 	};
 } __attribute__ ((packed));
 
-- 
1.6.3.3

Re: [PATCH/RFC 0/1] v4l: Add support for binary controls

[Hans Verkuil]

Hi Kamil!

On Monday 29 March 2010 11:53:05 Kamil Debski wrote:
> 
> Hello,
> 
> This patch introduces new type of v4l2 control - the binary control. It
> will be useful for exchanging raw binary data between the user space and
> the driver/hardware.
> 
> The patch is pretty small – basically it adds a new control type.
> 
> 1.  Reasons to include this new type
> - Some devices require data which are not part of the stream, but there
> are necessary for the device to work e.g. coefficients for transformation
> matrices.
> - String control is not suitable as it suggests that the data is a null
> terminated string. This might be important when printing debug information -
> one might output strings as they are and binary data in hex.
> 
> 2. How does the binary control work
> The binary control has been based on the string control. The principle of
> use is the same. It uses v4l2_ext_control structure to pass the pointer and
> size of the data. It is left for the driver to call the copy_from_user/
> copy_to_user function to copy the data.
> 
> 3. About the patch
> The patch is pretty small – it basically adds a new control type. 
> 
> Best wishes,
> 

I don't think this is a good idea. Controls are not really meant to be used
as an ioctl replacement.

Controls can be used to control the hardware via a GUI (e.g. qv4l2). Obviously,
this will fail for binary controls. Controls can also be used in cases where
it is not known up front which controls are needed. This typically happens for
bridge drivers that can use numerous combinations of i2c sub-devices. Each
subdev can have its own controls.

There is a grey area where you want to give the application access to low-level
parameters but without showing them to the end-user. This is currently not
possible, but it will be once the control framework is finished and once we
have the possibility to create device nodes for subdevs.

But what you want is to basically pass whole structs as a control. That's
something that ioctls where invented for. Especially once we have subdev nodes
this shouldn't be a problem.

Just the fact that it is easy to implement doesn't mean it should be done :-)

Do you have specific use-cases for your proposed binary control?

Regards,

	Hans

-- 
Hans Verkuil - video4linux developer - sponsored by TANDBERG

Re: [PATCH/RFC 0/1] v4l: Add support for binary controls

[Laurent Pinchart]

Hi Hans,

On Tuesday 30 March 2010 08:41:47 Hans Verkuil wrote:
> On Monday 29 March 2010 11:53:05 Kamil Debski wrote:
> > Hello,
> > 
> > This patch introduces new type of v4l2 control - the binary control. It
> > will be useful for exchanging raw binary data between the user space and
> > the driver/hardware.
> > 
> > The patch is pretty small – basically it adds a new control type.
> > 
> > 1.  Reasons to include this new type
> > - Some devices require data which are not part of the stream, but there
> > are necessary for the device to work e.g. coefficients for transformation
> > matrices.
> > - String control is not suitable as it suggests that the data is a null
> > terminated string. This might be important when printing debug
> > information - one might output strings as they are and binary data in
> > hex.
> > 
> > 2. How does the binary control work
> > The binary control has been based on the string control. The principle of
> > use is the same. It uses v4l2_ext_control structure to pass the pointer
> > and size of the data. It is left for the driver to call the
> > copy_from_user/ copy_to_user function to copy the data.
> > 
> > 3. About the patch
> > The patch is pretty small – it basically adds a new control type.
> > 
> > Best wishes,
> 
> I don't think this is a good idea. Controls are not really meant to be used
> as an ioctl replacement.
> 
> Controls can be used to control the hardware via a GUI (e.g. qv4l2).
> Obviously, this will fail for binary controls. Controls can also be used
> in cases where it is not known up front which controls are needed. This
> typically happens for bridge drivers that can use numerous combinations of
> i2c sub-devices. Each subdev can have its own controls.
> 
> There is a grey area where you want to give the application access to
> low-level parameters but without showing them to the end-user. This is
> currently not possible, but it will be once the control framework is
> finished and once we have the possibility to create device nodes for
> subdevs.
> 
> But what you want is to basically pass whole structs as a control. That's
> something that ioctls where invented for. Especially once we have subdev
> nodes this shouldn't be a problem.
> 
> Just the fact that it is easy to implement doesn't mean it should be done
> :-)
> 
> Do you have specific use-cases for your proposed binary control?

As discussed yesterday, here are a few use cases for the OMAP3 ISP driver.

- white balance matrix
- gamma correction tables

In both cases, the driver needs an array (possible 2 dimensional) of values to 
configure the hardware.

This can obviously be done using private ioctls, but what makes the red&blue 
white balance gains different from the white balance matrix ? Why should the 
first be controls and the later not ?

-- 
Regards,

Laurent Pinchart

Re: [PATCH/RFC 0/1] v4l: Add support for binary controls

[Andy Walls]

On Tue, 2010-03-30 at 10:57 +0200, Laurent Pinchart wrote:
> Hi Hans,
> 
> On Tuesday 30 March 2010 08:41:47 Hans Verkuil wrote:
> > On Monday 29 March 2010 11:53:05 Kamil Debski wrote:
> > > Hello,
> > > 
> > > This patch introduces new type of v4l2 control - the binary control. It
> > > will be useful for exchanging raw binary data between the user space and
> > > the driver/hardware.
> > > 
> > > The patch is pretty small – basically it adds a new control type.
> > > 
> > > 1.  Reasons to include this new type
> > > - Some devices require data which are not part of the stream, but there
> > > are necessary for the device to work e.g. coefficients for transformation
> > > matrices.
> > > - String control is not suitable as it suggests that the data is a null
> > > terminated string. This might be important when printing debug
> > > information - one might output strings as they are and binary data in
> > > hex.
> > > 
> > > 2. How does the binary control work
> > > The binary control has been based on the string control. The principle of
> > > use is the same. It uses v4l2_ext_control structure to pass the pointer
> > > and size of the data. It is left for the driver to call the
> > > copy_from_user/ copy_to_user function to copy the data.
> > > 
> > > 3. About the patch
> > > The patch is pretty small – it basically adds a new control type.
> > > 
> > > Best wishes,
> > 
> > I don't think this is a good idea. Controls are not really meant to be used
> > as an ioctl replacement.
> > 
> > Controls can be used to control the hardware via a GUI (e.g. qv4l2).
> > Obviously, this will fail for binary controls. Controls can also be used
> > in cases where it is not known up front which controls are needed. This
> > typically happens for bridge drivers that can use numerous combinations of
> > i2c sub-devices. Each subdev can have its own controls.
> > 
> > There is a grey area where you want to give the application access to
> > low-level parameters but without showing them to the end-user. This is
> > currently not possible, but it will be once the control framework is
> > finished and once we have the possibility to create device nodes for
> > subdevs.
> > 
> > But what you want is to basically pass whole structs as a control. That's
> > something that ioctls where invented for. Especially once we have subdev
> > nodes this shouldn't be a problem.
> > 
> > Just the fact that it is easy to implement doesn't mean it should be done
> > :-)
> > 
> > Do you have specific use-cases for your proposed binary control?
> 
> As discussed yesterday, here are a few use cases for the OMAP3 ISP driver.
> 
> - white balance matrix
> - gamma correction tables
> 
> In both cases, the driver needs an array (possible 2 dimensional) of values to 
> configure the hardware.
> 
> This can obviously be done using private ioctls, but what makes the red&blue 
> white balance gains different from the white balance matrix ? Why should the 
> first be controls and the later not ?

I'll suggest some tests:

1. Can an operator easily manipulate the control in an intuitive
fashion?

2. Can the kernel easily convey the visual form of the control to an
application, such the application can render it with common widget sets
not knowing much information apriori?



So sliders for gain controls fit that criteria easily.


I'm not sure about a matrix.  I'm guessing one could have a "look up
table" type control.  It would visually (on a gui) be a matrix of text
boxes that take numeric inputs; maybe with some kernel provided axes
labels and row and column labaels.  (I think that's better than an
arbitrary binary blob, although more work to implement.)


Regards,
Andy

RE: [PATCH/RFC 0/1] v4l: Add support for binary controls

[Kamil Debski]

> From: Hans Verkuil [mailto:hverkuil@xs4all.nl]
> 
> Hi Kamil!

Hi Hans,

> 
> On Monday 29 March 2010 11:53:05 Kamil Debski wrote:
> >
> > Hello,
> >
> > This patch introduces new type of v4l2 control - the binary control.
> It
> > will be useful for exchanging raw binary data between the user space
> and
> > the driver/hardware.
> >
> > The patch is pretty small – basically it adds a new control type.
> >
> > 1.  Reasons to include this new type
> > - Some devices require data which are not part of the stream, but
> there
> > are necessary for the device to work e.g. coefficients for
> transformation
> > matrices.
> > - String control is not suitable as it suggests that the data is a
> null
> > terminated string. This might be important when printing debug
> information -
> > one might output strings as they are and binary data in hex.
> >
> > 2. How does the binary control work
> > The binary control has been based on the string control. The
> principle of
> > use is the same. It uses v4l2_ext_control structure to pass the
> pointer and
> > size of the data. It is left for the driver to call the
> copy_from_user/
> > copy_to_user function to copy the data.
> >
> > 3. About the patch
> > The patch is pretty small – it basically adds a new control type.
> >
> > Best wishes,
> >
> 
> I don't think this is a good idea. Controls are not really meant to be
> used
> as an ioctl replacement.
> 
> Controls can be used to control the hardware via a GUI (e.g. qv4l2).
> Obviously,
> this will fail for binary controls. Controls can also be used in cases
> where
> it is not known up front which controls are needed. This typically
> happens for
> bridge drivers that can use numerous combinations of i2c sub-devices.
> Each
> subdev can have its own controls.
> 
> There is a grey area where you want to give the application access to
> low-level
> parameters but without showing them to the end-user. This is currently
> not
> possible, but it will be once the control framework is finished and
> once we
> have the possibility to create device nodes for subdevs.
> 
> But what you want is to basically pass whole structs as a control.
> That's
> something that ioctls where invented for. Especially once we have
> subdev nodes
> this shouldn't be a problem.
> 
> Just the fact that it is easy to implement doesn't mean it should be
> done :-)
> 
> Do you have specific use-cases for your proposed binary control?

Yes, I have. I am working on a driver for a video codec which is using 
the mem2mem framework. I have to admit it's a pretty difficult 
hardware to work with. It was one of the reasons for Pawel Osciak 
to add multiplane support to videobuf.

Before decoding, the hardware has to parse the header of the video
stream to get all necessary parameters such as the number of buffers,
width, height and some internal, codec specific stuff. The video stream
is then demultiplexed and divided into encoded frames in software and
the hardware can only process one, separated frame at a time.

The whole codec setup cannot be achieved by using VIDIOC_S_FMT call, 
because hardware requires access to the header data. I wanted to use
this binary control to pass the header to the codec after setting the
right format with VIDIOC_S_FMT. Then video frames can be easily decoded
as a standard calls to QBUF/DQBUF pairs.

It is similar for encoding - the basic parameters are set with
VIDIOC_S_FMT, then some codec specific/advanced are accessible as
standard v4l2 controls. Then the encoding engine is initialized and the
hardware returns an header of the output video stream. The header can
be acquired by getting the value of the binary control. After that the
frame to be encoded is provided and hw returns a single frame of
encoded stream. 

Using custom ioctls seems appropriate for a hardware specific driver.
Whereas the proposed binary control for getting and setting the video
stream header could be generic solution and can be used in many drivers
for hardware codecs.

Do You have any better solution for such device?

Best regards,
--
Kamil Debski
Linux Platform Group
Samsung Poland R&D Center

Re: [PATCH/RFC 0/1] v4l: Add support for binary controls

[Mauro Carvalho Chehab]

Kamil Debski wrote:
>> From: Hans Verkuil [mailto:hverkuil@xs4all.nl]
>>
>> Hi Kamil!
> 
> Hi Hans,
> 
>> On Monday 29 March 2010 11:53:05 Kamil Debski wrote:
>>> Hello,
>>>
>>> This patch introduces new type of v4l2 control - the binary control.
>> It
>>> will be useful for exchanging raw binary data between the user space
>> and
>>> the driver/hardware.
>>>
>>> The patch is pretty small – basically it adds a new control type.
>>>
>>> 1.  Reasons to include this new type
>>> - Some devices require data which are not part of the stream, but
>> there
>>> are necessary for the device to work e.g. coefficients for
>> transformation
>>> matrices.
>>> - String control is not suitable as it suggests that the data is a
>> null
>>> terminated string. This might be important when printing debug
>> information -
>>> one might output strings as they are and binary data in hex.
>>>
>>> 2. How does the binary control work
>>> The binary control has been based on the string control. The
>> principle of
>>> use is the same. It uses v4l2_ext_control structure to pass the
>> pointer and
>>> size of the data. It is left for the driver to call the
>> copy_from_user/
>>> copy_to_user function to copy the data.
>>>
>>> 3. About the patch
>>> The patch is pretty small – it basically adds a new control type.
>>>
>>> Best wishes,
>>>
>> I don't think this is a good idea. Controls are not really meant to be
>> used
>> as an ioctl replacement.
>>
>> Controls can be used to control the hardware via a GUI (e.g. qv4l2).
>> Obviously,
>> this will fail for binary controls. Controls can also be used in cases
>> where
>> it is not known up front which controls are needed. This typically
>> happens for
>> bridge drivers that can use numerous combinations of i2c sub-devices.
>> Each
>> subdev can have its own controls.
>>
>> There is a grey area where you want to give the application access to
>> low-level
>> parameters but without showing them to the end-user. This is currently
>> not
>> possible, but it will be once the control framework is finished and
>> once we
>> have the possibility to create device nodes for subdevs.
>>
>> But what you want is to basically pass whole structs as a control.
>> That's
>> something that ioctls where invented for. Especially once we have
>> subdev nodes
>> this shouldn't be a problem.
>>
>> Just the fact that it is easy to implement doesn't mean it should be
>> done :-)
>>
>> Do you have specific use-cases for your proposed binary control?
> 
> Yes, I have. I am working on a driver for a video codec which is using 
> the mem2mem framework. I have to admit it's a pretty difficult 
> hardware to work with. It was one of the reasons for Pawel Osciak 
> to add multiplane support to videobuf.
> 
> Before decoding, the hardware has to parse the header of the video
> stream to get all necessary parameters such as the number of buffers,
> width, height and some internal, codec specific stuff. The video stream
> is then demultiplexed and divided into encoded frames in software and
> the hardware can only process one, separated frame at a time.
> 
> The whole codec setup cannot be achieved by using VIDIOC_S_FMT call, 
> because hardware requires access to the header data. I wanted to use
> this binary control to pass the header to the codec after setting the
> right format with VIDIOC_S_FMT. Then video frames can be easily decoded
> as a standard calls to QBUF/DQBUF pairs.
> 
> It is similar for encoding - the basic parameters are set with
> VIDIOC_S_FMT, then some codec specific/advanced are accessible as
> standard v4l2 controls. Then the encoding engine is initialized and the
> hardware returns an header of the output video stream. The header can
> be acquired by getting the value of the binary control. After that the
> frame to be encoded is provided and hw returns a single frame of
> encoded stream. 
> 
> Using custom ioctls seems appropriate for a hardware specific driver.
> Whereas the proposed binary control for getting and setting the video
> stream header could be generic solution and can be used in many drivers
> for hardware codecs.
> 
> Do You have any better solution for such device?

For sure using custom CTRL's is wrong.

If I understood correctly, you want to send some mpeg transport stream
(or something like) to the hardware and let it decode, right?

For sure the current API spec don't cover such usecase. IMO, whatever decided,
we need to add an example for this non-trivial usage. 

On a first glance, by using what we currently have for V4L2 API, it seems that 
the more correct approach is to format with S_FMT as MPEG, using a "resolution" 
that will allocate a buffer with enough size for sending the stream
to the hardware (this is basically the way other mpeg-capable encoders/decoders
do). Then, send the header via the usual stream interface and retrieve
the stream information via VIDIOC_G_* ioctls. 

Only after having the header processed by the hardware, you'll be able to mmap
memory to receive the decoded streams.

I don't think we should add a custom ioctl for this case, as other hardware may
have similar requirements, but maybe we should, instead, just create a new set of
ioctl's for video processing.

-- 

Cheers,
Mauro

Re: [PATCH/RFC 0/1] v4l: Add support for binary controls

[Laurent Pinchart]

Hi Kamil,

On Tuesday 30 March 2010 14:26:00 Kamil Debski wrote:
> > From: Hans Verkuil [mailto:hverkuil@xs4all.nl]
> > On Monday 29 March 2010 11:53:05 Kamil Debski wrote:
> > > Hello,
> > > 
> > > This patch introduces new type of v4l2 control - the binary control. It
> > > will be useful for exchanging raw binary data between the user space and
> > > the driver/hardware.
> > > 
> > > The patch is pretty small – basically it adds a new control type.
> > > 
> > > 1.  Reasons to include this new type
> > > - Some devices require data which are not part of the stream, but there
> > > are necessary for the device to work e.g. coefficients for
> > > transformation matrices.
> > > - String control is not suitable as it suggests that the data is a
> > > null terminated string. This might be important when printing debug
> > > information - one might output strings as they are and binary data in
> > > hex.
> > > 
> > > 2. How does the binary control work
> > > The binary control has been based on the string control. The principle
> > > of use is the same. It uses v4l2_ext_control structure to pass the
> > > pointer and size of the data. It is left for the driver to call the
> > > copy_from_user/copy_to_user function to copy the data.
> > > 
> > > 3. About the patch
> > > The patch is pretty small – it basically adds a new control type.
> > > 
> > 
> > I don't think this is a good idea. Controls are not really meant to be
> > used as an ioctl replacement.
> > 
> > Controls can be used to control the hardware via a GUI (e.g. qv4l2).
> > Obviously, this will fail for binary controls. Controls can also be used
> > in cases where it is not known up front which controls are needed. This
> > typically happens for bridge drivers that can use numerous combinations of
> > i2c sub-devices. Each subdev can have its own controls.
> > 
> > There is a grey area where you want to give the application access to
> > low-level parameters but without showing them to the end-user. This is
> > currently not possible, but it will be once the control framework is
> > finished and once we have the possibility to create device nodes for
> > subdevs.
> > 
> > But what you want is to basically pass whole structs as a control.
> > That's something that ioctls where invented for. Especially once we have
> > subdev nodes this shouldn't be a problem.
> > 
> > Just the fact that it is easy to implement doesn't mean it should be
> > done :-)
> > 
> > Do you have specific use-cases for your proposed binary control?
> 
> Yes, I have. I am working on a driver for a video codec which is using
> the mem2mem framework. I have to admit it's a pretty difficult
> hardware to work with. It was one of the reasons for Pawel Osciak
> to add multiplane support to videobuf.
> 
> Before decoding, the hardware has to parse the header of the video
> stream to get all necessary parameters such as the number of buffers,
> width, height and some internal, codec specific stuff. The video stream
> is then demultiplexed and divided into encoded frames in software and
> the hardware can only process one, separated frame at a time.
> 
> The whole codec setup cannot be achieved by using VIDIOC_S_FMT call,
> because hardware requires access to the header data. I wanted to use
> this binary control to pass the header to the codec after setting the
> right format with VIDIOC_S_FMT. Then video frames can be easily decoded
> as a standard calls to QBUF/DQBUF pairs.

In that case I have to agree with Hans, a private ioctl is better.

> It is similar for encoding - the basic parameters are set with
> VIDIOC_S_FMT, then some codec specific/advanced are accessible as
> standard v4l2 controls. Then the encoding engine is initialized and the
> hardware returns an header of the output video stream. The header can
> be acquired by getting the value of the binary control. After that the
> frame to be encoded is provided and hw returns a single frame of
> encoded stream.
> 
> Using custom ioctls seems appropriate for a hardware specific driver.
> Whereas the proposed binary control for getting and setting the video
> stream header could be generic solution and can be used in many drivers
> for hardware codecs.

I don't think it would. The format of the data is pretty much hardware 
specific. If you can make the format generic, then the private ioctl could 
become generic.

> Do You have any better solution for such device?

-- 
Regards,

Laurent Pinchart

RE: [PATCH/RFC 0/1] v4l: Add support for binary controls

[Kamil Debski]

Hi Mauro,

Mauro Carvalho Chehab wrote:
> Kamil Debski wrote:
> >> From: Hans Verkuil [mailto:hverkuil@xs4all.nl]
> >>
> >> Hi Kamil!
> >
> > Hi Hans,
> >
> >> On Monday 29 March 2010 11:53:05 Kamil Debski wrote:
> >>> Hello,
> >>>
> >>> This patch introduces new type of v4l2 control - the binary
> control.
> >> It
> >>> will be useful for exchanging raw binary data between the user
> space
> >> and
> >>> the driver/hardware.
> >>>
> >>> The patch is pretty small – basically it adds a new control type.
> >>>
> >>> 1.  Reasons to include this new type
> >>> - Some devices require data which are not part of the stream, but
> >> there
> >>> are necessary for the device to work e.g. coefficients for
> >> transformation
> >>> matrices.
> >>> - String control is not suitable as it suggests that the data is a
> >> null
> >>> terminated string. This might be important when printing debug
> >> information -
> >>> one might output strings as they are and binary data in hex.
> >>>
> >>> 2. How does the binary control work
> >>> The binary control has been based on the string control. The
> >> principle of
> >>> use is the same. It uses v4l2_ext_control structure to pass the
> >> pointer and
> >>> size of the data. It is left for the driver to call the
> >> copy_from_user/
> >>> copy_to_user function to copy the data.
> >>>
> >>> 3. About the patch
> >>> The patch is pretty small – it basically adds a new control type.
> >>>
> >>> Best wishes,
> >>>
> >> I don't think this is a good idea. Controls are not really meant to
> be
> >> used
> >> as an ioctl replacement.
> >>
> >> Controls can be used to control the hardware via a GUI (e.g. qv4l2).
> >> Obviously,
> >> this will fail for binary controls. Controls can also be used in
> cases
> >> where
> >> it is not known up front which controls are needed. This typically
> >> happens for
> >> bridge drivers that can use numerous combinations of i2c sub-
> devices.
> >> Each
> >> subdev can have its own controls.
> >>
> >> There is a grey area where you want to give the application access
> to
> >> low-level
> >> parameters but without showing them to the end-user. This is
> currently
> >> not
> >> possible, but it will be once the control framework is finished and
> >> once we
> >> have the possibility to create device nodes for subdevs.
> >>
> >> But what you want is to basically pass whole structs as a control.
> >> That's
> >> something that ioctls where invented for. Especially once we have
> >> subdev nodes
> >> this shouldn't be a problem.
> >>
> >> Just the fact that it is easy to implement doesn't mean it should be
> >> done :-)
> >>
> >> Do you have specific use-cases for your proposed binary control?
> >
> > Yes, I have. I am working on a driver for a video codec which is
> using
> > the mem2mem framework. I have to admit it's a pretty difficult
> > hardware to work with. It was one of the reasons for Pawel Osciak
> > to add multiplane support to videobuf.
> >
> > Before decoding, the hardware has to parse the header of the video
> > stream to get all necessary parameters such as the number of buffers,
> > width, height and some internal, codec specific stuff. The video
> stream
> > is then demultiplexed and divided into encoded frames in software and
> > the hardware can only process one, separated frame at a time.
> >
> > The whole codec setup cannot be achieved by using VIDIOC_S_FMT call,
> > because hardware requires access to the header data. I wanted to use
> > this binary control to pass the header to the codec after setting the
> > right format with VIDIOC_S_FMT. Then video frames can be easily
> decoded
> > as a standard calls to QBUF/DQBUF pairs.
> >
> > It is similar for encoding - the basic parameters are set with
> > VIDIOC_S_FMT, then some codec specific/advanced are accessible as
> > standard v4l2 controls. Then the encoding engine is initialized and
> the
> > hardware returns an header of the output video stream. The header can
> > be acquired by getting the value of the binary control. After that
> the
> > frame to be encoded is provided and hw returns a single frame of
> > encoded stream.
> >
> > Using custom ioctls seems appropriate for a hardware specific driver.
> > Whereas the proposed binary control for getting and setting the video
> > stream header could be generic solution and can be used in many
> drivers
> > for hardware codecs.
> >
> > Do You have any better solution for such device?
> 
> For sure using custom CTRL's is wrong.
> 
> If I understood correctly, you want to send some mpeg transport stream
> (or something like) to the hardware and let it decode, right?
> 
> For sure the current API spec don't cover such usecase. IMO, whatever
> decided,
> we need to add an example for this non-trivial usage.
> 
> On a first glance, by using what we currently have for V4L2 API, it
> seems that
> the more correct approach is to format with S_FMT as MPEG, using a
> "resolution"
> that will allocate a buffer with enough size for sending the stream
> to the hardware (this is basically the way other mpeg-capable
> encoders/decoders
> do). Then, send the header via the usual stream interface and retrieve
> the stream information via VIDIOC_G_* ioctls.
> 
> Only after having the header processed by the hardware, you'll be able
> to mmap
> memory to receive the decoded streams.
> 
> I don't think we should add a custom ioctl for this case, as other
> hardware may
> have similar requirements, but maybe we should, instead, just create a
> new set of
> ioctl's for video processing.

We are using elementary streams which are divided in software to header
and encoded frames. The idea behind the binary control was keeping 
consistence between 1 QBUF on source video stream and 1 QBUF on output
video stream. That was my motivation for the binary control. 

When decoding, the header would be passed to the driver with the binary
control, and when encoding it would be read through the binary control.

If I understand your suggestion, decoding at the beginning would require
an extra QBUF/DQBUF on source video stream, before mmaping the buffers for
output video frames. Similar for encoding - one extra QBUF/DQBUF for output
stream at the beginning.

It seems reasonable, if I discard the assumption that a QBUF on one queue
(source) corresponds to one QBUF on the other queue (output).

Best regards,
--
Kamil Debski
Linux Platform Group
Samsung Poland R&D Center

Re: [PATCH/RFC 0/1] v4l: Add support for binary controls

[Mauro Carvalho Chehab]

Kamil Debski wrote:
> Hi Mauro,
> 
> Mauro Carvalho Chehab wrote:
>> Kamil Debski wrote:
>>>> From: Hans Verkuil [mailto:hverkuil@xs4all.nl]
>>>>
>>>> Hi Kamil!
>>> Hi Hans,
>>>
>>>> On Monday 29 March 2010 11:53:05 Kamil Debski wrote:
>>>>> Hello,
>>>>>
>>>>> This patch introduces new type of v4l2 control - the binary
>> control.
>>>> It
>>>>> will be useful for exchanging raw binary data between the user
>> space
>>>> and
>>>>> the driver/hardware.
>>>>>
>>>>> The patch is pretty small – basically it adds a new control type.
>>>>>
>>>>> 1.  Reasons to include this new type
>>>>> - Some devices require data which are not part of the stream, but
>>>> there
>>>>> are necessary for the device to work e.g. coefficients for
>>>> transformation
>>>>> matrices.
>>>>> - String control is not suitable as it suggests that the data is a
>>>> null
>>>>> terminated string. This might be important when printing debug
>>>> information -
>>>>> one might output strings as they are and binary data in hex.
>>>>>
>>>>> 2. How does the binary control work
>>>>> The binary control has been based on the string control. The
>>>> principle of
>>>>> use is the same. It uses v4l2_ext_control structure to pass the
>>>> pointer and
>>>>> size of the data. It is left for the driver to call the
>>>> copy_from_user/
>>>>> copy_to_user function to copy the data.
>>>>>
>>>>> 3. About the patch
>>>>> The patch is pretty small – it basically adds a new control type.
>>>>>
>>>>> Best wishes,
>>>>>
>>>> I don't think this is a good idea. Controls are not really meant to
>> be
>>>> used
>>>> as an ioctl replacement.
>>>>
>>>> Controls can be used to control the hardware via a GUI (e.g. qv4l2).
>>>> Obviously,
>>>> this will fail for binary controls. Controls can also be used in
>> cases
>>>> where
>>>> it is not known up front which controls are needed. This typically
>>>> happens for
>>>> bridge drivers that can use numerous combinations of i2c sub-
>> devices.
>>>> Each
>>>> subdev can have its own controls.
>>>>
>>>> There is a grey area where you want to give the application access
>> to
>>>> low-level
>>>> parameters but without showing them to the end-user. This is
>> currently
>>>> not
>>>> possible, but it will be once the control framework is finished and
>>>> once we
>>>> have the possibility to create device nodes for subdevs.
>>>>
>>>> But what you want is to basically pass whole structs as a control.
>>>> That's
>>>> something that ioctls where invented for. Especially once we have
>>>> subdev nodes
>>>> this shouldn't be a problem.
>>>>
>>>> Just the fact that it is easy to implement doesn't mean it should be
>>>> done :-)
>>>>
>>>> Do you have specific use-cases for your proposed binary control?
>>> Yes, I have. I am working on a driver for a video codec which is
>> using
>>> the mem2mem framework. I have to admit it's a pretty difficult
>>> hardware to work with. It was one of the reasons for Pawel Osciak
>>> to add multiplane support to videobuf.
>>>
>>> Before decoding, the hardware has to parse the header of the video
>>> stream to get all necessary parameters such as the number of buffers,
>>> width, height and some internal, codec specific stuff. The video
>> stream
>>> is then demultiplexed and divided into encoded frames in software and
>>> the hardware can only process one, separated frame at a time.
>>>
>>> The whole codec setup cannot be achieved by using VIDIOC_S_FMT call,
>>> because hardware requires access to the header data. I wanted to use
>>> this binary control to pass the header to the codec after setting the
>>> right format with VIDIOC_S_FMT. Then video frames can be easily
>> decoded
>>> as a standard calls to QBUF/DQBUF pairs.
>>>
>>> It is similar for encoding - the basic parameters are set with
>>> VIDIOC_S_FMT, then some codec specific/advanced are accessible as
>>> standard v4l2 controls. Then the encoding engine is initialized and
>> the
>>> hardware returns an header of the output video stream. The header can
>>> be acquired by getting the value of the binary control. After that
>> the
>>> frame to be encoded is provided and hw returns a single frame of
>>> encoded stream.
>>>
>>> Using custom ioctls seems appropriate for a hardware specific driver.
>>> Whereas the proposed binary control for getting and setting the video
>>> stream header could be generic solution and can be used in many
>> drivers
>>> for hardware codecs.
>>>
>>> Do You have any better solution for such device?
>> For sure using custom CTRL's is wrong.
>>
>> If I understood correctly, you want to send some mpeg transport stream
>> (or something like) to the hardware and let it decode, right?
>>
>> For sure the current API spec don't cover such usecase. IMO, whatever
>> decided,
>> we need to add an example for this non-trivial usage.
>>
>> On a first glance, by using what we currently have for V4L2 API, it
>> seems that
>> the more correct approach is to format with S_FMT as MPEG, using a
>> "resolution"
>> that will allocate a buffer with enough size for sending the stream
>> to the hardware (this is basically the way other mpeg-capable
>> encoders/decoders
>> do). Then, send the header via the usual stream interface and retrieve
>> the stream information via VIDIOC_G_* ioctls.
>>
>> Only after having the header processed by the hardware, you'll be able
>> to mmap
>> memory to receive the decoded streams.
>>
>> I don't think we should add a custom ioctl for this case, as other
>> hardware may
>> have similar requirements, but maybe we should, instead, just create a
>> new set of
>> ioctl's for video processing.
> 
> We are using elementary streams which are divided in software to header
> and encoded frames. The idea behind the binary control was keeping 
> consistence between 1 QBUF on source video stream and 1 QBUF on output
> video stream. That was my motivation for the binary control. 
> 
> When decoding, the header would be passed to the driver with the binary
> control, and when encoding it would be read through the binary control.
> 
> If I understand your suggestion, decoding at the beginning would require
> an extra QBUF/DQBUF on source video stream, before mmaping the buffers for
> output video frames. Similar for encoding - one extra QBUF/DQBUF for output
> stream at the beginning.

Yes, that's what I'm proposing as a way for the decoder to automatically detect
the format of the input stream.

For encoding, the better approach is to use the CTRLs that control the MPEG
parameters, adding more if your hardware support other formats than what's 
currently available at the API. In this case, create one control per variable
that needs to be configured (bit stream, audio format, video format, etc).

In any case, reading the encoder/decoder parameters via CTRL should return
the format used by the hardware.

> It seems reasonable, if I discard the assumption that a QBUF on one queue
> (source) corresponds to one QBUF on the other queue (output).

I don't think you should have any type of assumption between the input and the
output. I can imagine some cases where the number of buffers will be different.
For example, if you have a TS with multiple PID's inside, some mem2mem hardware
may be able to filter the PID's. So, at the output, you'll have less buffers.

Cheers,
Mauro