Introduction

The purpose of this page is to describe the Linux V4L2 driver for Xilinx Gamma Correction LUT soft IP.

To understand more details about this IP and its functionality please see the Product Guide (below).

The Xilinx V4L2 Gamma LUT driver (xilinx-gamma.c) is based on the V4L2 framework and creates a subdev node(/dev/v4l-subdev*)

which can be used to configure the the Look Up Table (LUT) for Red, Green and Blue gamma correction components.

The LUT is applied to the incoming video stream by the Gamma Correction LUT soft IP.

The driver is available at https://github.com/Xilinx/linux-xlnx/blob/master/drivers/media/platform/xilinx/xilinx-gamma.c

The Gamma Correction LUT soft IP provides a way to apply correction to each Red, Green and Blue components.

Exposes a V4L2 control to program Red, Green and Blue gamma values.
- A gamma of 0.1 is achieved by setting a value of 1 (minumum)
- A gamma of 1.0 is achieved by setting a value of 10 (default)
- A gamma of 4.0 is achieved by setting a value of 40 (maximum)

media-ctl will show an entry as follows that represents the Gamma LUT V4L2 sub-device. :

- entity 16: a0050000.gamma (2 pads, 2 links)
type V4L2 subdev subtype Unknown flags 0
device node name /dev/v4l-subdev4
pad0: Sink
[fmt:RBG24/1280x720 field:none]
<- "a0060000.demosaic":1 [ENABLED]
pad1: Source
[fmt:RBG24/1280x720 field:none]
-> "a0040000.csc":0 [ENABLED]

yavta can display the three controls as follows :

[root@plnx_aarch64 /]$ yavta --no-query -l /dev/v4l-subdev4
Device /dev/v4l-subdev4 opened.
--- User Controls (class 0x00980001) ---
control 0x0098c9c1 `Red Gamma Correction(1 = 0.1 & ' min 1 max 40 step 1 default 10 current 10.
control 0x0098c9c2 `Blue Gamma Correction(1 = 0.1 &' min 1 max 40 step 1 default 10 current 10.
control 0x0098c9c3 `Green Gamma Correction(1 = 0.1 ' min 1 max 40 step 1 default 10 current 1
[root@plnx_aarch64 /]$ yavta --no-query -w '0x0098c9c1 40' /dev/v4l-subdev4
Device /dev/v4l-subdev4 opened.
Control 0x0098c9c1 set to 40, is 40
[root@plnx_aarch64 /]$ yavta --no-query -w '0x0098c9c2 40' /dev/v4l-subdev4
Device /dev/v4l-subdev4 opened.
Control 0x0098c9c2 set to 40, is 40
[root@plnx_aarch64 /]$ yavta --no-query -w '0x0098c9c3 40' /dev/v4l-subdev4
Device /dev/v4l-subdev4 opened.
Control 0x0098c9c3 set to 40, is 40
[root@plnx_aarch64 /]$ yavta --no-query -l /dev/v4l-subdev4
Device /dev/v4l-subdev4 opened.
--- User Controls (class 0x00980001) ---
control 0x0098c9c1 `Red Gamma Correction(1 = 0.1 & ' min 1 max 40 step 1 default 10 current 40.
control 0x0098c9c2 `Blue Gamma Correction(1 = 0.1 &' min 1 max 40 step 1 default 10 current 40.
control 0x0098c9c3 `Green Gamma Correction(1 = 0.1 ' min 1 max 40 step 1 default 10 current 40.
3 controls found.

IP/Driver Features

IP Features	2018.1 and on wards
IP version	1.0
Programmable gamma table supports gamma correction or any user defined function	Yes*
Three channel independent look-up table structure	Yes*
One, two, four or eight pixel-wide AXI4-Stream video interface	Yes
8 and 10 bits per component support	Yes**
Supports spatial resolutions from 64 x 64 up to 8192 x 4320	Yes***
Supports 4K60 in all supported device families	NA

*Pre-computed coefficients table used.

**Media bus format supported is MEDIA_BUS_FMT_RBG888_1X24 for both 8 and 10bpc

***Tested for 8192x4320, 3840x2160, 1920x1080, 1280x720

Kernel Configuration

CONFIG_VIDEO_XILINX_GAMMA and CONFIG_VIDEO_XILINX should be enabled.

Device Tree Binding

The device tree node should be defined with correct hardware configuration. How to define the node is documented here:
https://github.com/Xilinx/linux-xlnx/blob/master/Documentation/devicetree/bindings/media/xilinx/xlnx%2Cv-gamma-lut.txt

Testing Procedure

This driver is a V4L2 sub-device driver, which means it is designed to operate with a video device in it's graph. The driver has been tested with a Xilinx video device (a V4L2 capture device) that is backed by
a DMA element (like Framebuffer Write IP). The V4L2 device driver for this IP cannot be tested in isolation by itself. The successful operation of the driver can be tested in two phases :

Successful Creation of a Media Device
Successful Frame Captures (or writing of buffers by the Frame-buffer Write IP)

Successful Creation of a Media Device

media-ctl is a Linux user space utility that can control media entities, it is a part of a larger set of V4L2 tools called v4l-utils
media-ctl allows you to print the topology of your media pipeline and specify input and output pad properties.

Successful Frame Captures

Please see the Test Approach section of the Frame Buffer Write Wiki for more details on how to capture frames.

Test design

We need a ZCU102 Rev 1.0 board. Enable TPG, Demosaic, Gamma LUT and Framebuffer Write in kernel defconfig.

Modify the demosaic driver as below as TPG output is RGB type and Demosaic requires SRGGB type.

44 diff --git a/drivers/media/platform/xilinx/xilinx-demosaic.c b/drivers/media/platform/xilinx/xilinx-demosaic.c     
45 index 505fc14..8594dba 100644
46 --- a/drivers/media/platform/xilinx/xilinx-demosaic.c
47 +++ b/drivers/media/platform/xilinx/xilinx-demosaic.c
48 @@ -141,6 +141,7 @@ static bool
49  xdmsc_is_format_bayer(struct xdmsc_dev *xdmsc, u32 code)
50  {
51         switch (code) {
52 +       case MEDIA_BUS_FMT_RBG888_1X24:
53         case MEDIA_BUS_FMT_SRGGB8_1X8:
54                 xdmsc->bayer_fmt = XDEMOSAIC_RGGB;
55                 break;

Setup the TPG to generate a pattern.
Setup the Gamma brightness as shown above.
Now capture image using yavta

root@zcu102-zynqmp:/media# media-ctl -V '"a3c30000.v_tpg":0 [fmt:RBG24/1280x720 field:none]'
root@zcu102-zynqmp:/media# ./tpg_diag_1080p_setup.sh 2
Device /dev/v4l-subdev2 opened.
--- User Controls (class 0x00980001) ---
control 0x0098c903 `Test Pattern: Color Mask' min 0 max 7 step 0 default 0 current 0.
control 0x0098c907 `Test Pattern: Motion Speed' min 0 max 255 step 1 default 4 current 4.
control 0x0098c908 `Test Pattern: Cross Hairs Row' min 0 max 4095 step 1 default 100 current 100.
control 0x0098c909 `Test Pattern: Cross Hairs Colum' min 0 max 4095 step 1 default 100 current 100.
control 0x0098c90a `Test Pattern: Zplate Horizontal' min 0 max 65535 step 1 default 30 current 30.
control 0x0098c90b `Test Pattern: Zplate Horizontal' min 0 max 65535 step 1 default 0 current 0.
control 0x0098c90c `Test Pattern: Zplate Vertical S' min 0 max 65535 step 1 default 1 current 1.
control 0x0098c90d `Test Pattern: Zplate Vertical S' min 0 max 65535 step 1 default 0 current 0.
control 0x0098c90e `Test Pattern: Box Size' min 0 max 4095 step 1 default 50 current 50.
control 0x0098c90f `Test Pattern: Box Color(RGB/YCb' min 0 max 16777215 step 1 default 0 current 0.
control 0x0098c912 `Test Pattern: Foreground Patter' min 0 max 2 step 1 default 0 current 0.
  0: No Overlay (*)
  1: Moving Box
  2: Cross Hairs
--- Image Source Controls (class 0x009e0001) ---
control 0x009e0901 `Vertical Blanking' min 3 max 8159 step 1 default 100 current 100.
control 0x009e0902 `Horizontal Blanking' min 3 max 8159 step 1 default 100 current 100.
--- Image Processing Controls (class 0x009f0001) ---
control 0x009f0903 `Test Pattern' min 0 max 16 step 1 default 9 current 9.
  1: Horizontal Ramp
  2: Vertical Ramp
  3: Temporal Ramp
  4: Solid Red
  5: Solid Green
  6: Solid Blue
  7: Solid Black
  8: Solid White
  9: Color Bars (*)
  10: Zone Plate
  11: Tartan Color Bars
  12: Cross Hatch
  13: Color Sweep
  14: Vertical/Horizontal Ramps
  15: Black/White Checker Board
  16: PseudoRandom
14 controls found.
Device /dev/v4l-subdev2 opened.
Control 0x009e0901 set to 45, is 45
Device /dev/v4l-subdev2 opened.
Control 0x009f0903 set to 14, is 14
Device /dev/v4l-subdev2 opened.
Control 0x0098c912 set to 1, is 1
Device /dev/v4l-subdev2 opened.
Control 0x0098c90f set to 8453889, is 8453889
Device /dev/v4l-subdev2 opened.
--- User Controls (class 0x00980001) ---
control 0x0098c903 `Test Pattern: Color Mask' min 0 max 7 step 0 default 0 current 0.
control 0x0098c907 `Test Pattern: Motion Speed' min 0 max 255 step 1 default 4 current 4.
control 0x0098c908 `Test Pattern: Cross Hairs Row' min 0 max 4095 step 1 default 100 current 100.
control 0x0098c909 `Test Pattern: Cross Hairs Colum' min 0 max 4095 step 1 default 100 current 100.
control 0x0098c90a `Test Pattern: Zplate Horizontal' min 0 max 65535 step 1 default 30 current 30.
control 0x0098c90b `Test Pattern: Zplate Horizontal' min 0 max 65535 step 1 default 0 current 0.
control 0x0098c90c `Test Pattern: Zplate Vertical S' min 0 max 65535 step 1 default 1 current 1.
control 0x0098c90d `Test Pattern: Zplate Vertical S' min 0 max 65535 step 1 default 0 current 0.
control 0x0098c90e `Test Pattern: Box Size' min 0 max 4095 step 1 default 50 current 50.
control 0x0098c90f `Test Pattern: Box Color(RGB/YCb' min 0 max 16777215 step 1 default 0 current 8453889.
control 0x0098c912 `Test Pattern: Foreground Patter' min 0 max 2 step 1 default 0 current 1.
  0: No Overlay
  1: Moving Box (*)
  2: Cross Hairs
--- Image Source Controls (class 0x009e0001) ---
control 0x009e0901 `Vertical Blanking' min 3 max 8159 step 1 default 100 current 45.
control 0x009e0902 `Horizontal Blanking' min 3 max 8159 step 1 default 100 current 100.
--- Image Processing Controls (class 0x009f0001) ---
control 0x009f0903 `Test Pattern' min 0 max 16 step 1 default 9 current 14.
  1: Horizontal Ramp
  2: Vertical Ramp
  3: Temporal Ramp
  4: Solid Red
  5: Solid Green
  6: Solid Blue
  7: Solid Black
  8: Solid White
  9: Color Bars
  10: Zone Plate
  11: Tartan Color Bars
  12: Cross Hatch
  13: Color Sweep
  14: Vertical/Horizontal Ramps (*)
  15: Black/White Checker Board
  16: PseudoRandom
14 controls found.
root@zcu102-zynqmp:/media# yavta -n 3 -c10 -f RGB24 -s 1280x720 --skip 9 -F /dev/video0
Device /dev/video0 opened.
Device `vcap_gama output 0' on `platform:vcap_gama:0' is a video output (without mplanes) device.
Video format set: RGB24 (33424752) 1280x720 field none, 1 planes: 
 * Stride 3840, buffer size 2764800
Video format: RGB24 (33424752) 1280x720 field none, 1 planes: 
 * Stride 3840, buffer size 2764800
3 buffers requested.
length: 1 offset: 3944269120 timestamp type/source: mono/EoF
Buffer 0/0 mapped at address 0x7f97c11000.
length: 1 offset: 3944269120 timestamp type/source: mono/EoF
Buffer 1/0 mapped at address 0x7f9796e000.
length: 1 offset: 3944269120 timestamp type/source: mono/EoF
Buffer 2/0 mapped at address 0x7f976cb000.
0 (0) [-] none 0 0 B 76.889014 76.889033 0.488 fps ts mono/EoF
1 (1) [-] none 1 0 B 77.912628 77.912645 0.977 fps ts mono/EoF
2 (2) [-] none 2 0 B 78.936243 78.936258 0.977 fps ts mono/EoF
3 (0) [-] none 3 0 B 79.959858 79.959873 0.977 fps ts mono/EoF
4 (1) [-] none 4 0 B 80.983388 80.983490 0.977 fps ts mono/EoF
5 (2) [-] none 5 0 B 82.007087 82.007104 0.977 fps ts mono/EoF
6 (0) [-] none 6 0 B 83.030702 83.030719 0.977 fps ts mono/EoF
7 (1) [-] none 7 0 B 84.054317 84.054334 0.977 fps ts mono/EoF
8 (2) [-] none 8 0 B 85.077921 85.078025 0.977 fps ts mono/EoF
9 (0) [-] none 9 0 B 86.101451 86.101468 0.977 fps ts mono/EoF
Captured 10 frames in 11.259807 seconds (0.888115 fps, 0.000000 B/s).
3 buffers released.
root@zcu102-zynqmp:/media#

View the captured image using a viewer like yuvplayer.exe

Boards Supported

Driver has been tested on following boards:

ZCU102 Rev 1.0

Known Issues

AR68768 - LogiCORE Gamma LUT - Release Notes and Known Issues for the Vivado 2017.3 tool and later versions

Changelog

2024.1

No changes

2023.2

No changes

2023.1

No changes

2022.2

No changes

2022.1

No changes

2021.2

No changes

2021.1

No changes

2020.2

Summary
- Fix Coverity warnings
Commits
- v4l: xilinx-gamma: Fix warnings for UNUSED_VALUE
- v4l: xilinx-gamma: Fix warnings for NULL_RETURNS

2020.1

Summary
- No changes

2019.2

Summary
- No changes

2019.1

Summary
- Make max-width and max-height mandatory dt properties
Commits
- 489fb29 v4l: xilinx-gamma: Make max-width and max-height mandatory dt properties

2018.3

Summary
- Added xlnx,max-width and xlnx,max-height dt properties
- Added checks to set the correct default, min and max width and height from dt properties
Commits
- da376b3 v4l: xilinx-gamma: Add check for max width and height
- 032026f v4l: xilinx-gamma: Correct default values when max width, height dt property absent

2018.2

Summary
- No changes

2018.1

Summary
- Added 10-bit support and kernel documentation
- Fixed debug mode compile error
Commits
- 1d34b87 v4l: xilinx-gamma: Fix compile error in debug mode
- ada9c6a v4l: xilinx-gamma: Add kernel-doc for xgamma_dev struct
- ae6e1f0 v4l: xilinx-gamma: Add 10-bit IP support for Video Gammma IP.

2017.4

Summary
- No changes

2017.3

Summary
- Initial revision added to master branch
Commits
- ea3529b v4l: xilinx-gamma: Correct return value checking
- 4e91c3f v4l: xilinx-gamma: initial driver support for xilinx video gamma lut ip

Xilinx Wiki

Xilinx V4L2 Gamma Correction LUT driver

Table of Contents