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 (DTO) 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 |
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:
hback-porch
hfront-porch
vback-porch
vfront-porch
hsync-len
vsync-len
by using the open source reference available at the following path https://www.epanorama.net/faq/vga2rgb/calc.html .
LDB Structure format:
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 | Q7 module | HDMI LVDS |
|
μQ7-962 | μQ7 module | HDMI LVDS |
|
μQ7-A75-J | μQ7 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
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.
LVDS Customization Guide for i.MX8
The MIPI DSI support on i.MX8-based boards is enabled via the device trees located in the Kernel source at arch/arm64/boot/dts/seco. MIPI-DSI on i.MX8 with IPU is supported with Synopsys hardware while i.MX8 uses the Mixel and the Advantec panels.
SECO boards with i.MX8 SoC support the following MIPI-DSI interfaces:
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 LCDIF
i.MX8M boards come with 2 display controllers, DCSS and LCDIF:
DCCS can be connected to HDMI, DP or MIPI-DSI and supports up to 4K resolution;
LCDIF 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 added in the Linux Device Tree overlay and the panel must be enabled in Device tree.
The process of designing a Device Tree Overlay includes the three following macro steps:
writing a Device Tree Overlay (.dts) file;
generating a *.dtbo file, output of *.dts file build;
enabling the overlay through *.dtbo file.
To obtain the information about the overlay device tree, you can refer to the documentation available into the kernel:
linux-seco/Documentation/devicetree/overlay-notes.txt
Using the documentation above you can customize the Device Tree Overlay, as well as enable and disable functionalities.
Embedded displays often do not have a dedicated DDC (e.g., parallel RGB, LVDS, or similar display links), and therefore the system needs to be told exactly what display resolution and timing have to be supplied.
Embedded displays without DDC channel (parallel RGB/LVDS) use a fixed mode provided by the driver, this can be either:
display modes from a display driver (used for kernel mode settings (KMS) e.g. from
panel-simple.c, e.g., i.MX8 DRM driver);display modes from a specific devicetree overlay (support available only from BSP 9 onwards);
KMS interface (Kernel Mode Setting, part of the Direct Rendering Manager (DRM) interface, kernel argument, through Xorg/RandR using modesetting driver).
Adding Custom LVDS support in panel-simple.c for i.MX8*
The connected panel is represented in the device tree in its own node. That node references the used LDB/LVDS channel through its node 'port'.One can either use the panel-simple or the panel-lvds driver, both options are outlined below.
Panel Simple
Set the property 'compatible' to an existing or newly added panel from the panel-simple driver.
linux-seco/drivers/gpu/drm/panel/panel-simple.c
To obtain information about panel-simple.txt, you can refer to the documentation presents into the kernel:
linux-seco/Documentation/devicetree/bindings/display/panel/simple-panel.txt
To configure custom display timing for AUO Panel model p215
The kernel writes Timing in panel-simple.c and directly matches with short strings. There are the following statements in the drivers/gpu/drm/panel/panel-simple.c file
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 */
}
};
MODULE_DEVICE_TABLE(of, platform_of_match);
MODULE_DEVICE_TABLE(of, platform_of_match); The timing parameters are configured in the structure
auo,p215hca-high.
After the timing parameter need to call the device tree file with compatible device on the panel.
Please refer the respective SECO boards device tree (.dts)file.
For eg: seco-imx8mm-c72.dts
panel_lvds: lvds_panel {
compatible = "auo,p215hca-high";
#address-cells = <1>;
#size-cells = <0>;
};
After the panel configuration customer needs to configure bridge with the file:
linux-seco/arch/arm64/boot/dts/seco/overlays/seco-imx8mm-c72-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 panel configuration it is necessary to configure correctly 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,
refer tosn65dsi84 datasheetfor more informations.lvds,preserve-dsi-timings: this parameter is usefull when LVDS display timing are synchronized with Data Enable, it should be removed if the panel is not DE sync. The LVDS panel that are not synchronized with Data Enable must be configured without lvds,preserve-dsi-timing parameter and clocks = <&si5351a 0> should be commented out to ensure timing sync.
All this configurations can be useless in some cases, so the panel can’t turn on.
This is attributable to i.MX8 DSI video driver that recalculates the panel timing to adapt them to 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 turn on.
SECO preconfigured Panels
Below some pre-built device tree overlay files for i.MX8 boards. Once the setup has been defined, kernel, including LVDS display resolution, can be built. After the compilation, please copy the file into device and boot the board by setting up the custom device tree file with support of seco_config file.
Device tree display overlay for i.MX8
Board | Module | Peripheral | Overlays |
|---|---|---|---|
C12 | SMARC | MIPI-DSI to LVDS, HDMI |
|
C20 | SBC | MIPI-DSI to LVDS, HDMI |
|
C25 | Q7 | MIPI-DSI to LVDS, MIPI-DSI to eDP, HDMI |
|
C26 | Q7 | LVDS, DP, HDMI |
|
C43 | SBC | MIPI-DSI to eDP, LVDS, HDMI |
|
C72 | μQ7 | MIPI-DSI to LVDS, MIPI-DSI to eDP |
|
C61 | SBC | MIPI-DSI to LVDS, MIPI-DSI to eDP |
|
C57 | SBC | MIPI-DSI to eDP, LVDS |
|
D16 | SMARC | MIPI-DSI to eDP, LVDS, HDMI |
|
Since BSP9.0 , Our images comes with pre-built available overlays binaries as (.dtbo).
In Linux BSP 9.0 you can list these files available on the boot partition,
For eg: 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 done, you can boot the board using seco_config tool to configure the Device tree overlay, Below are the commands to 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 boot up with your display configuration.
Successfully board has been booted with selected display device tree.