The aim of this section is to properly configure the LVDS settings.
The LVDS Display Bridge (LDB) is used to connect the IPU (Image Processing Unit) to the External LVDS Display Interface. Its purpose is to support the flow of synchronous RGB data from the IPU to external display devices through the LVDS interface.
Device Tree Overlay
The Device Tree Overlays (DTBO) provide a way to modify the overall device tree without re-compiling the complete device tree.
Overlays are fragments of a complete device tree that can be included or removed according to the environment. The direct consequence is enabling/disabling the hardware components of the system.
The design process of a Device Tree Overlay includes three macro steps:
writing a Device Tree Overlay (.dts) file;
generating a *.dtbo file, output of *.dts file build;
enabling the overlay through *.dtbo file.
For further information on the Device Tree Overlay customization, please refer to the documentation available at following Kernel path:
linux-seco/Documentation/devicetree/overlay-notes.txt
Some devices are used in the overlays and those devices are pre-enabled by default in the source.
Below is the reference table for the pre-enabled Device Tree Overlay.
Boards Family | Peripherals | Device Tree Overlay |
|---|---|---|
i.MX6 | UART, LVDS, RGB, Audio, HDMI, Touch, GPIO, Pin header selection, etc. |
|
i.MX8 | HDMI, Display Port, LVDS , Camera, hdmiin, lcdif, Modem, eDP, GPIO,CAN, RTC,PCIe, SPI, DCSS, WiFi/BT, etc. |
|
LVDS Customization Guide for i.MX6
The i.MX6-based boards use the fbdev interface for mode setting and output configuration.
There are two IPU units on the i.mx6q SoC, and only one IPU unit on the i.mx6dl SoC. Each IPU unit has two display interfaces. The Vivante X driver can only make use of the first framebuffer /dev/fb0, while the others can be used through the fbdev framebuffer interface.
The assignment of the possible display outputs to the framebuffers (scan-out engines) and their timing configuration can be done both through Kernel command line and within the device tree. The command line settings take precedence over the device tree.
The first and third video output has an additional overlay framebuffer configured.
Video output | IPU core | fb boot name | fb device | Overlay fb device |
|---|---|---|---|---|
First | IPU1 | mxcfb0 | /dev/fb0 | /dev/fb1 |
Second | IPU1 | mxcfb1 | /dev/fb2 | |
Third | IPU2 | mxcfb2 | /dev/fb3 | /dev/fb4 |
Fourth | IPU2 | mxcfb3 | /dev/fb5 |
Kernel: Adding Custom LVDS support in Device tree file for i.MX6
Please follow the steps below to add the custom display timing data into the imx6qdl-seco_lvds_display.dtsi file.
Verify the signal timing specifications of the LCD in the datasheet and then calculate following parameters:
Parameter | Definition |
|---|---|
hback-porch | Horizontal Back Porch (HBP) - Number of pixel clock pulses between HSYNC signal and the first valid pixel data. |
hfront-porch | HoriHorizontal Front porch (HFP) - Number of pixel clock pulses between the last valid pixel data in the line and the next HSYNC pulse. |
vback-porch | Vertical Back Porch (VBP) - Number of lines (HSYNC pulses) from a VSYNC signal to the first valid line. |
vfront-porch | Vertical Front Porch (VFP) - Number of lines (HSYNC pulses) between the last valid line of the frame and the next VSYNC pulse. |
hsync-len | Number of PIXCLK pulses when a HSYNC signal is active. |
vsync-len | Number of HSYNC pulses when a VSYNC signal is active. |
by using the open source reference available at the following path https://www.epanorama.net/faq/vga2rgb/calc.html .
To obtain the information about the ldb structure, you can refer to the documentation available into the Kernel:
linux-seco/Documentation/devicetree/bindings/display/imx/ldb.txt linux-seco/Documentation/devicetree/bindings/fb/fsl_ipuv3_fb.txt
timing9: $name {
clock-frequency = <$Clock-frequency>;
hactive = <$Hactive>;
vactive = <$Vactive>;
hback-porch = <$Hback>;
hfront-porch = <$Hfront>;
vback-porch = <$Vback>;
vfront-porch = <$Vfront>;
hsync-len = <$Hsync>;
vsync-len = <$Vsync>;
};
Below is the sample timing data for SVGA TFT LCD(800x600) 10.4 inches (BA104S01-100):
name = LBD-SVGA-BA
Clock-frequency = 39600000
Hactive = 800
Vactive = 600
Hback = 45
Hfront = 45
Vback = 25
Vfront = 25
Hsync = 10
Vsync = 10
After that, get into the device tree path (arch/arm/boot/dts/imx6qdl-seco_lvds_display.dtsi).
Please find below the ldb structure to be added in the imx6qdl-seco_lvds_display.dtsi file.
cd linux-seco/arch/arm/boot/dts vi imx6qdl-seco_lvds_display.dtsi
Now add the newly created lbd structure into the LVDS device tree file and save the file.
You can now check the Device Tree Overlay file whether the LVDS (LDB) is enabled or not. Below is the example to enable the ldb node.
fragment@3 {
target = <&ldb>;
__overlay__ {
status = "okay";
};
};
Once the setup is done, you can compile the source.
From BSP9.0 onwards, the LVDS is enabled by the Device Tree Overlay file, using seco_config tool to load the the device tree overlay in U-Boot level.
Device tree display overlay for i.MX6
Board | Type of product | Peripheral | Overlays |
|---|---|---|---|
Q7-928 | Qseven module | HDMI LVDS |
|
μQ7-962 | μQseven module | HDMI LVDS |
|
μQ7-A75-J | μQseven module | HDMI LVDS |
|
SBC-A62-J | SBC | HDMI LVDS Sitronix touch(st1232) Goodix Touch(gt928) |
|
SBC-B08 | SBC | LVDS RGB |
|
SYS-B07-7 | System | ||
SBC-C23 | SBC | LVDS |
|
From BSP9.0 onwards, our images comes with available pre-built overlays binaries as (.dtbo).
In Linux BSP 9.0, you can list the available files on the boot partition.
For example, with the SBC-A62-J:
ls -l boot/ total 8532 -rw-r--r-- 1 secospa secospa 69897 Sep 16 13:17 imx6dl-seco_SBC_A62.dtb -rw-r--r-- 1 secospa secospa 72 Sep 16 13:17 imx6qdl-seco_SBC_A62_conn_j8.dtbo -rw-r--r-- 1 secospa secospa 307 Sep 16 13:17 imx6qdl-seco_SBC_A62_touch_gt928.dtbo -rw-r--r-- 1 secospa secospa 311 Sep 16 13:17 imx6qdl-seco_SBC_A62_touch_st1232.dtbo -rw-r--r-- 1 secospa secospa 942 Sep 16 13:17 imx6qdl-seco_SBC_A62_video_HDMI.dtbo -rw-r--r-- 1 secospa secospa 1556 Sep 16 13:17 imx6qdl-seco_SBC_A62_video_HDMI_LVDS.dtbo -rw-r--r-- 1 secospa secospa 812 Sep 16 13:17 imx6qdl-seco_SBC_A62_video_LVDS.dtbo -rw-r--r-- 1 secospa secospa 1556 Sep 16 13:17 imx6qdl-seco_SBC_A62_video_LVDS_HDMI.dtbo -rw-r--r-- 1 secospa secospa 955 Sep 16 13:17 imx6qdl-seco_SBC_A62_video_LVDSx2_CLONE.dtbo -rw-r--r-- 1 secospa secospa 1088 Sep 16 13:17 imx6qdl-seco_SBC_A62_video_LVDSx2_DUAL.dtbo -rw-r--r-- 1 secospa secospa 71563 Sep 16 13:17 imx6q-seco_SBC_A62.dtb
U-Boot: Adding Custom LVDS resolution into list
The resolition to use is passed from U-Boot to the kernel via bootargs. The "seco_config" command help the user to perform the selection of the video settings and resolution.
In order to add a new custom LVDS resolution follow this step:
Edit file <u-boot src>/cmd/cmd_seco_config.c
This file contains the list of display setting to pass to kernel via bootargs.
The selection is performend via seco_config command.
Add the custom resolution setting with a new item into the follow structure:
static lvds_video_spec_t lvds_video_spec_list [] = {
{ "WVGA [800x480]", "LDB-WVGA", "RGB666", "datamap=spwg", "", 1 },
{ "SVGA [800x600]", "LDB-SVGA", "RGB666", "datamap=spwg", "", 1 },
{ "XGA [1024x768]", "LDB-XGA", "RGB666", "datamap=spwg", "", 1 },
{ "WXGA [1368x768]", "LDB-WXGA", "RGB24", "datamap=jeida", "", 1 },
{ "WXGAP60 [1280x800]", "LDB-1280P60", "RGB24,bpp=32","datamap=spwg", "", 1 },
{ "SXGA [1280x1024]", "LDB-SXGA", "RGB24", "datamap=jeida", "", 1 },
{ "HD1080 [1920x1080]", "LDB-1080P60", "RGB24", "datamap=spwg", "ldb=spl0", 2 },
{<DISPLAY NAME>, <KERNEL DISPLAY NAME>, <PIXEL FORMAT>, <DATA MAPPING>, "LDB SETTING", <CHANNEL NUMBER>}
};
with:
DISPLAY NAME: name show into the resolution list when seco_config command is used
KERNEL DISPLAY NAME: name of the resolution added into the kernel file arch/arm/boot/dts/imx6qdl-seco_lvds_display.dtsi ($name variable)
PIXEL FORMAT: isplay interface pixel format as below:
RGB666 IPU_PIX_FMT_RGB666
RGB565 IPU_PIX_FMT_RGB565
RGB24 IPU_PIX_FMT_RGB24
BGR24 IPU_PIX_FMT_BGR24
GBR24 IPU_PIX_FMT_GBR24
YUV444 IPU_PIX_FMT_YUV444
YUYV IPU_PIX_FMT_YUYV
UYVY IPU_PIX_FMT_UYVY
YVYV IPU_PIX_FMT_YVYU
VYUY IPU_PIX_FMT_VYUY
DATA MAPPING: color signals mapping order [ jeida | spwg | vesa ]
LDB SETTING: i.MX6 LVDS setting. Leave empty to use the default (display single channel).
(ldb=spl0 -> split mode, used for display dual channel)
CHANNEL NUMBER: number of channel to use (leave 1 for default configuration)
Once it is done, you can boot the board using seco_config tool to configure the Device Tree Overlay.
Below are the commands for the setup:
MX6QDLS SBC-A62 U-Boot > seco_config
__________________________________________________
Chose Video Setting.
__________________________________________________
1) no display
2) LVDS
3) HDMI
4) LVDS - LVDS (clone)
5) LVDS - LVDS (dual)
6) LVDS - HDMI
7) HDMI - LVDS
> 2
__________________________________________________
Chose LVDS resolution for LVDS1.
__________________________________________________
1) WVGA [800x480]
2) SVGA [800x600]
3) XGA [1024x768]
4) WXGA [1368x768]
5) WXGAP60 [1280x800]
6) SXGA [1280x1024]
7) HD1080 [1920x1080]
> 1
__________________________________________________
Chose FDT overlay option for touch screen controller.
__________________________________________________
1) not use
2) st1232
3) gt928
> 2
__________________________________________________
Chose FDT overlay option for J8 Expansion Connector configurator.
__________________________________________________
1) defalut
2) custom
> 1
Saving Environment to MMC... Writing to MMC(1)... OK
X6QDLS SBC-A62 U-Boot > saveenv
Saving Environment to MMC... Writing to MMC(1)... OK
MX6QDLS SBC-A62 U-Boot > printenv fdt_file
fdt_file=imx6q-seco_SBC_A62.dtb
MX6QDLS SBC-A62 U-Boot > printenv fdt_overlay_video_list
fdt_overlay_video_list=imx6qdl-seco_SBC_A62_video_LVDS.dtbo
MX6QDLS SBC-A62 U-Boot > printenv fdt_overlay_per_list
fdt_overlay_per_list=imx6qdl-seco_SBC_A62_touch_st1232.dtbo
MX6QDLS SBC-A62 U-Boot > boot
SECO i.MX Distro with XWayload backend 4.19-warrior secoboards ttymxc1
secoboards login: root
password:
ast login: Thu Sep 16 06:50:45 UTC 2021 on tty7
root@secoboards:~#
The board has now successfully been loaded with LVDS and Touch (st1232) dtbo file.
Display Customization Guide for i.MX8
The MIPI DSI support on i.MX8-based boards is configured via the overlays device trees located in the Kernel sources at arch/arm64/boot/dts/seco/overlays.
SECO boards with i.MX8 SoC support the following MIPI-DSI interface to LVDS / eDP bridges:
Texas Instruments SN65DSI84 MIPI® DSI bridge to FlatLink™ LVDS single-channel DSI to dual-link LVDS bridge;
Texas Instruments SN65DSI86 Dual-channel MIPI® DSI to embedded DisplayPort™ (eDP ) bridge.
DCSS vs eLCDIF
i.MX8M boards come with 2 display controllers, DCSS and eLCDIF:
DCCS can be connected to HDMI, DP or MIPI-DSI and supports up to 4K resolution;
eLCDIF can be connected only to MIPI-DSI and supports up to 1080p resolution.
All the drivers on the boards enabled by the i.MX8, i.MX8M Mini, i.MX8M Nano, i.MX8X and i.MX8M Plus families of processors are integrated into the Linux kernel's DRM/KMS subsystem.
The Display Interface should be configured in the Linux Device Tree and in the Linux kernel driver panel-simple.c. The bridge configuration for the panel LVDS or eDP must be inserted in the Seco preconfigured dtbo files.
For LVDS:
seco-imx8mq-c12-dcss-sn65dsi84-overlay.dts seco-imx8mq-c12-lcdif-sn65dsi84-overlay.dts seco-imx8mq-c20-dcss-sn65dsi84-overlay.dts seco-imx8mq-c25-dcss-sn65dsi84-overlay.dts seco-imx8mm-c72-lcdif-sn65dsi84-overlay.dts seco-imx8mm-c61-lcdif-sn65dsi84-overlay.dts
For eDP:
seco-imx8mq-c25-dcss-sn65dsi86-overlay.dts seco-imx8mm-c61-lcdif-sn65dsi86-overlay.dts seco-imx8mm-c72-lcdif-sn65dsi86-overlay.dts
Adding Custom LVDS / eDP panel support in panel-simple.c for i.MX8
The configured panel is represented by the following nodes located in the board device tree, for example arch/arm64/boot/dts/seco/seco-imx8mm-c61.dts:
panel_edp: edp_panel {
compatible = "boe,ev156fhm";
#address-cells = <1>;
#size-cells = <0>;
};
panel_lvds: lvds_panel {
compatible = "auo,p215hca-high";
#address-cells = <1>;
#size-cells = <0>;
};
These nodes represent the links between the device tree and the panel-simple.c structure.
Set the compatible property to an existing or newly added panel from the panel-simple driver.
linux-seco/drivers/gpu/drm/panel/panel-simple.c
Example: Configure the custom display timing for AUO Panel model p215hca
In the Seco BSP's the references panels are configured and tested with 10000 on/off cycle. Below the panel structure from drivers/gpu/drm/panel/panel-simple.c for LVDS 1920x1080 from Seco BSP9:
static const struct display_timing auo_p215hca_high_timing = {
.pixelclock = { 139000000, 160000000, 165000000 },
.hactive = { 1920, 1920, 1920 },
.hfront_porch = { 1, 85, 90 },
.hsync_len = { 1, 10, 45 },
.hback_porch = { 1, 85, 150 },
.vactive = { 1080, 1080, 1080 },
.vfront_porch = { 3, 20, 50 },
.vsync_len = { 6, 10,60 },
.vback_porch = { 11, 20, 37 },
.flags = DISPLAY_FLAGS_HSYNC_LOW |
DISPLAY_FLAGS_VSYNC_LOW |
DISPLAY_FLAGS_DE_LOW |
DISPLAY_FLAGS_PIXDATA_NEGEDGE,
};
static const struct panel_desc auo_p215hca_high = {
.timings = &auo_p215hca_high_timing,
.num_timings = 1,
.bpc = 8,
.size = {
.width = 68,
.height = 121,
},
.delay = {
/*
* The panel spec recommends one second delay
* to the below items. However, it's a bit too
* long in pratical. Based on tests, it turns
* out 100 milliseconds is fine.
*/
.prepare = 100,
.enable = 100,
.unprepare = 100,
.disable = 100,
},
.bus_format = MEDIA_BUS_FMT_RGB888_1X24,//MEDIA_BUS_FMT_RGB888_1X7X4_SPWG,
};
static const struct of_device_id platform_of_match[] = {
{
}, {
.compatible = "auo,p215hca-high",
.data = &auo_p215hca_high,
}, {
/* sentinel */
}
};
In this case the configured panel is the: auo,p215hca-high, all the parameters configured in struct display_timing are derived from panel datasheet.
After setup panel configuration, you need to check for LVDS the following file (for eDP this part can be skipped):
linux-seco/arch/arm64/boot/dts/seco/overlays/seco-imx8mm-c61-lcdif-sn65dsi84-overlay.dts
This is the content:
target = <&adv_bridge>;
__overlay__ {
#address-cells = <1>;
#size-cells = <0>;
lvds,datamap = "jeida";
lvds,dual-channel;
lvds,channel-swap;
lvds,preserve-dsi-timings;
/*include/drm/drm_mipi_dsi.h*/
dsi,mode-flags = <0x805>; /*MIPI_DSI_MODE_VIDEO*/
clocks = <&si5351a 0>;
status = "okay";
};
To complete bridge configuration, it is necessary to correctly configure the following parameters:
lvds,datamap: can be configured as jeida or spwg, other configurations are not supported.
lvds,dual-channel: if inserted, it enables bridge dual channel output. The DSI video signal is splitted in LVDS channel A and LVDS channel B.
lvds,preserve-dsi-timings: this parameter is useful when the LVDS display timing is synchronized with Data Enable, while it should be removed if the panel is not DE sync. LVDS panels that are not synchronized with Data Enable must be configured without
lvds,preserve-dsi-timing parameterandclocks = <&si5351a 0>should be commented out to ensure timing sync.
The above configurations can be useless in some cases and prevent the panel from turning on.
This is due to the i.MX8 DSI video driver that recalculates the panel timing to adapt them to the i.MX8 DSI video output. In these cases, a fine tuning in the admitted panel timing is necessary: clocks, front and back porch until the LVDS panel turns on.
SECO preconfigured Panels
Below are some pre-built Device Tree Overlay files for i.MX8-based boards.
Once the setup has been defined, the Kernel, including LVDS display resolution, can be built. After compiling, please copy the file into the device and boot the board by setting up the custom device tree file with the support of seco_config file.
Device tree display overlay for i.MX8
Board | Type of product | Peripheral | Overlays |
|---|---|---|---|
SM-C12 | SMARC module | MIPI-DSI to LVDS |
|
SBC-C20 | SBC | MIPI-DSI to LVDS |
|
Q7-C25 | Qseven module | MIPI-DSI to LVDS MIPI-DSI to eDP |
|
μQ7-C72 | μQseven module | MIPI-DSI to LVDS MIPI-DSI to eDP |
|
SBC-C61 | SBC | MIPI-DSI to LVDS MIPI-DSI to eDP |
|
SBC-C57 | SBC | MIPI-DSI to eDP |
|
SM-D16 | SMARC module | MIPI-DSI to eDP |
|
From BSP9.0 onwards, our images comes with available pre-built overlays binaries as (.dtbo).
In Linux BSP 9.0, you can list the available files on the boot partition.
For example, with the μQ7-C72:
ls -l boot/ total 25604 -rw-r--r-- 1 secospa secospa 26073600 Sep 16 02:55 Image -rw-r--r-- 1 secospa secospa 6000 Sep 16 02:55 imx8mm_m4_TCM_hello_world.bin -rw-r--r-- 1 secospa secospa 16528 Sep 16 02:55 imx8mm_m4_TCM_rpmsg_lite_pingpong_rtos_linux_remote.bin -rw-r--r-- 1 secospa secospa 16028 Sep 16 02:55 imx8mm_m4_TCM_rpmsg_lite_str_echo_rtos.bin -rw-r--r-- 1 secospa secospa 40092 Sep 16 02:55 imx8mm_m4_TCM_sai_low_power_audio.bin -rw-r--r-- 1 secospa secospa 53688 Sep 16 02:55 seco-imx8mm-c72.dtb -rw-r--r-- 1 secospa secospa 2140 Sep 16 02:55 seco-imx8mm-c72-lcdif-sn65dsi84.dtbo -rw-r--r-- 1 secospa secospa 1797 Sep 16 02:55 seco-imx8mm-c72-lcdif-sn65dsi86.dtbo
Once it is done, you can boot the board using seco_config tool to configure the Device Tree Overlay.
Below are the commands for the setup:
u-boot seco c72=> seco_config __________________________________________________ Choose boot Device for Kernel. __________________________________________________ 1) eMMC onboard 2) uSD onboard 3) TFTP 4) USB > 1 Choose the partition > 1 Path of the Kernel (enter for default Image) > __________________________________________________ Choose boot Device for FDT. __________________________________________________ 1) eMMC onboard 2) uSD onboard 3) TFTP 4) USB > 1 Choose the partition > 1 Path of the FDT (enter for default seco-imx8mq-c12.dtb) > __________________________________________________ Choose boot Device for FileSystem. __________________________________________________ 1) eMMC onboard 2) uSD onboard 3) NFS 4) USB > 1 Choose the partition > 2 __________________________________________________ Choose Video Output Configuration. __________________________________________________ 1) no video - no dtbo 2) eDP LCDIF-1920x1080 - seco-imx8mm-c72-lcdif-sn65dsi86.dtbo 3) LVDS LCDIF-1920x1080 - seco-imx8mm-c72-lcdif-sn65dsi84.dtbo > 2 __________________________________________________ Choose Board Options. __________________________________________________ 1) No addons > 1 Saving Environment to MMC... Writing to MMC(0)... OK
By selecting the dtbo to perform, the board will boot with your display configuration.
The board has now successfully been loaded with the selected display device tree.