Hi Sakari,
On 11/08/2011 10:55 PM, Sakari Ailus wrote:
Hi all,
This RFC discusses the SUBDEV_S_SELECTION/SUBDEV_G_SELECTION API which is
intended to amend and replace the existing SUBDEV_[SG]_CROP API. These
IOCTLs have previously been discussed in the Cambridge V4L2 brainstorming
meeting [0] and their intent is to provide more configurability for subdevs,
including cropping on the source pads and composing for a display.
The S_SELECTION patches for V4L2 nodes are available here [1] and the
existing documentation for the V4L2 subdev pad format configuration can be
found in [2].
SUBDEV_[SG]_SELECTION is intended to fully replace SUBDEV_[SG]_CROP in
drivers as the latter can be implemented in SUBDEV_[SG]_SELECTION using
active CROP target on sink pads. That can be done in v4l2-ioctl.c so drivers
only will need to implement SUBDEV_[SG]_SELECTION.
Questions, comments and thoughts are welcome, especially regarding new use
cases.
Order of configuration
======================
Sorry, what is exactly the SOURCE pad and SINK pad? The spec says "Data
flows from a source pad to a sink pad.". Does in refer to a subdev or to
a link? Look at the image below:
data ---- link0 --> (pad0) [subdev] (pad1) ----> link1
From subdev's point of view, pad0 is data source, pad1 is the sink.
From link0's point of view, pad0 is a data sink. Which interpretation
is correct?
The proposed order of the subdev configuration is as follows. Individual
steps may be omitted since any of the steps will reset the rectangles /
sizes for any following step.
I assume that SOURCE and SINK are defined from the link's point of view.
Otherwise it would mean that configuration goes in order opposite to
data flow order.
I do not think that resetting is a good idea. It is better to state in
spec that change of a given target guarantee that targets/formats
earlier in pipeline are not modified. Part below pipeline may change or
not. The application should check if the configuration of lower parts of
pipeline is suitable. For example
Change of COMPOSE target on SINK pad must not modify
- format on the SINK pad
- CROP on the SINK pad
All other parameters may change. Of course the configuration of lower
part must be consistent with higher part of the pipeline.
1. SUBDEV_S_FMT on the SINK pad. The user will issue SUBDEV_S_FMT to set the
subdev sink pad image size and media bus format code and other parameters in
v4l2_mbus_framefmt as necessary.
2. SUBDEV_S_SELECTION with CROP target on the SINK pad. The crop rectangle
is set related to the image size given in step 1).
3. SUBDEV_S_SELECTION with COMPOSE target on the SINK pad. The size of the
compose rectangle, if it differs from the size of the rectangle given in 2),
signifies user's wish to perform scaling.
4. SUBDEV_S_SELECTION with CROP target on the SOURCE pad. Configure cropping
performed by the subdev after scaling.
5. SUBDEV_S_SELECTION with COMPOSE target on the SOURCE pad. This configures
composition on the display if relevant for the subdevice. (In this case the
COMPOSE bounds will yield to the size of the display.)
6. SUBDEV_S_FMT on the SOURCE pad. The size of the image is defined by
setting CROP on the SOURCE pad, so SUBDEV_S_FMT only has an effect of
changing other parameters than size.
As defined in [2], when performing any of the configuration phases above,
the formats and selections are reset to defaults from each phase onwards.
For example, SUBDEV_S_SELECTION with CROP target on the SINK pad will
--- beyond its obvious function of setting CROP selection target on the SINK
pad --- reset the COMPOSE selection target on SINK pad, as well as the CROP
selection target and format on the SOURCE pad.
I think that formal definitions of CROP,COMPOSE for pads are needed.
As I remember from Cambridge brainstorming we agreed that SINK.COMPOSE
and SOURCE.CROP are expressed in subdev's internal coordinate system.
The SINK.CROP is expressed in link0's coordinate system and
SOURCE.COMPOSE is expressed in link1's coordinate system.
Definitions
===========
/**
* struct v4l2_subdev_selection - selection info
*
* @which: either V4L2_SUBDEV_FORMAT_ACTIVE or V4L2_SUBDEV_FORMAT_TRY
* @pad: pad number, as reported by the media API
* @target: selection target, used to choose one of possible rectangles
* @flags: constraints flags
* @r: coordinates of selection window
* @reserved: for future use, rounds structure size to 64 bytes, set to zero
*
* Hardware may use multiple helper window to process a video stream.
* The structure is used to exchange this selection areas between
* an application and a driver.
*/
struct v4l2_subdev_selection {
__u32 which;
__u32 pad;
__u32 target;
__u32 flags;
struct v4l2_rect r;
__u32 reserved[8];
};
Both SUBDEV_S_SELECTION and SUBDEV_G_SELECTION would take struct
v4l2_subdev_selection as the IOCTL argument (RW).
The same target definitions and flags apply as in [1], with possible
exception of the PADDED targets --- see below. The flags will gain _SUBDEV
prefix after the existing V4L2 prefix.
Sample use cases
================
OMAP 3 ISP preview
------------------
The OMAP 3 ISP preview block provides cropping on preview sink pad, but also
horizontal averaging. The horizontal averaging may scale the image
horizontally by factor 1/n, where n is either 1, 2, 4 or 8.
The preview block also performs pixel format conversion from raw bayer to
YUV. Other image processing operations crops maximum of 12 columns and 8 rows
before the format conversion. After the format conversion, further 2 columns
are cropped.
To make this easy for the user, the driver assumes that all the features
affecting cropping are enabled at all times so the size stays constant for
the user.
This example only includes the preview subdev since it can be shown
independently. In the example, the preview subdev is configured to crop the
image by 100 pixels on all sides of the image. The horizontal averaging is
configured by factor 1/2, which translates 100 pixels from each side of the
original image. The preview sink pad format is 800x600 SGRBG10.
[crop] 0:preview:1 [crop (static), compose]
The initial state of the pipeline is:
preview:0 preview:1
compose (0,0)/788x592 (0,0)/788x592
crop (7,4)/788x592 (1,0)/786x592
fmt 800x600/SGRBG10 786x592/YUYV
This is due to hardware imposed cropping performed in the sink pad
as well as on the source pad.
To crop 100 pixels on all sides:
SUBDEV_S_SELECTION(preview:0, CROP_ACTIVE, (99,100)/602x400);
The hardware mandated crop on the sink pad is thus one pixel on left
and right sides of the image. (This would also be shown in the
CROP_BOUNDS target.)
preview:0 preview:1
compose (0,0)/602x400 (0,0)/602x400
crop (99,100)/602x400 (1,0)/600x400
fmt 800x600/SGRBG10 600x400/YUYV
A sensor
--------
The intent is to obtain a VGA image from a 8 MP sensor which provides
following pipeline:
pixel_array:0 [crop] ---> 0:binner:1 ---> [crop] 0:scaler:1 [crop]
Binner is an entity which can perform scaling, but only in factor of 1/n,
where n is a positive integer. No cropping is needed. The intent is to get a
640x480 image from such sensor. (This doesn't involve any other
configuration as the image size related one.)
The initial state of the pipeline
pixel_array:0 binner:0 binner:1 scaler:0 scaler:1
compose (0,0)/3600x2464 (0,0)/3600x2464 (0,0)/3600x2464 (0,0)/3600x2464 (0,0)/3600x2464
crop (0,0)/3600x2464 (0,0)/3600x2464 (0,0)/3600x2464 (0,0)/3600x2464 (0,0)/3600x2464
fmt 3600x2464 3600x2464 3600x2464 3600x2464 3600x2464
This will configure the binning on the binner subdev sink pad:
SUBDEV_S_SELECTION(binner:0, COMPOSE_ACTIVE, (0,0)/1800x1232);
pixel_array:0 binner:0 binner:1 scaler:0 scaler:1
compose (0,0)/3600x2464 (0,0)/1800x1232 (0,0)/1800x1232 (0,0)/3600x2464 (0,0)/3600x2464
crop (0,0)/3600x2464 (0,0)/3600x2464 (0,0)/1800x1232 (0,0)/3600x2464 (0,0)/3600x2464
fmt 3600x2464 3600x2464 1800x1232 3600x2464 3600x2464
The same format must be set on the scaler pad 0 as well. This will
reset the size inside the scaler to a sane default, which is no
scaling:
SUBDEV_S_FMT(scaler:0, 1800x1232);
pixel_array:0 binner:0 binner:1 scaler:0 scaler:1
compose (0,0)/3600x2464 (0,0)/1800x1232 (0,0)/1800x1232 (0,0)/1800x1232 (0,0)/1800x1232
crop (0,0)/3600x2464 (0,0)/3600x2464 (0,0)/1800x1232 (0,0)/1800x1232 (0,0)/1800x1232
fmt 3600x2464 3600x2464 1800x1232 1800x1232 1800x1232
I assume that scaler can upscale image 1800x1232 on scaler:0 to
3600x2464 on pad scaler:1. Therefore the format and compose targets on
scaler:1 should not be changed.
To perform further scaling on the scaler, the COMPOSE target is used
on the scaler subdev's SOURCE pad:
SUBDEV_S_SELECTION(scaler:0, COMPOSE_ACTIVE, (0,0)/640x480);
pixel_array:0 binner:0 binner:1 scaler:0 scaler:1
compose (0,0)/3600x2464 (0,0)/1800x1232 (0,0)/1800x1232 (0,0)/640x480 (0,0)/640x480
crop (0,0)/3600x2464 (0,0)/3600x2464 (0,0)/1800x1232 (0,0)/1800x1232 (0,0)/640x480
fmt 3600x2464 3600x2464 1800x1232 1800x1232 640x480
It is possible to compose 640x480 image into 1800x1232 data stream
produced on scaler:1. Therefore the format on scaler:1 should not be
changed. The area outside 640x480 would left undefined or filled by some
pattern configured using controls. This situation was the reason of
introducing PADDED target.
Best regards,
Tomasz Stanislawski
The result is a 640x480 image from the scaler's output pad. The aspect ratio
of the resulting image is different from 4/3 since no cropping was
performed in this example.
Applications which do not recognise SUBDEV_S_SELECTION
======================================================
The current spec [2] tells that the scaling factor is defined by using
SUBDEV_S_FMT in the source pad. This method would not be supported in the
future, possibly affecting applications which use SUBDEV_S_FMT to configure
the scaling factor.
If supporting this is seen necessary, it can be implemented by e.g.
reverting to the old behaviour if the SOURCE crop rectangle width or height
is different from width and height specified in SOURCE S_FMT.
Open questions
==============
1. Keep subdev configuration flag. In Cambourne meeting the case of the OMAP
3 ISP resizer configuration dilemma was discussed, and the proposal was to
add a flag to disable propagating the configuration inside a single subdev.
Propagating inside a single subdev is the default. Where do we need this
flag; is just SUBDEV_S_SELECTION enough? [0]
2. Are PADDED targets relevant for media bus formats? [3]
References
==========
[0] http://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg35361.html
[1] http://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg36206.html
[2] http://hverkuil.home.xs4all.nl/spec/media.html#subdev
[3] http://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg36203.html
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