The aim of this section is to properly configure custom display: LVDS and eDP panels.
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.
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Standard Display Timings
Verify the signal timing specifications of the LCD in the datasheet and then calculate following parameters:
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Parameter
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Definition
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| Table of Contents |
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| Info |
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External references are available here: |
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Standard Display Timings
Verify the signal timing specifications of the LCD in the datasheet and then calculate following parameters:
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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 Horizontal 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. |
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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.
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Video output
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IPU core
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fb boot name
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fb device
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Overlay fb device
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First
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IPU1
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mxcfb0
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/dev/fb0
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/dev/fb1
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Second
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IPU1
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mxcfb1
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/dev/fb2
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Third
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IPU2
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mxcfb2
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/dev/fb3
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/dev/fb4
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Fourth
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IPU2
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mxcfb3
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/dev/fb5
Kernel: Adding Custom LVDS support in Device tree file for i.MX6
To obtain the information about the ldb structure, you can refer to the documentation available into the Kernel:
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In order to bring up a custom display, follow the steps below.
1. Kernel: Adding Custom LVDS support in Device tree file
The target file to be edited is linux-seco/arch/arm/boot/dts/imx6qdl-seco_lvds_display.dtsi. This one contains the list of available LVDS resolutions.
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cd linux-seco/arch/arm/boot/dts
vi imx6qdl-seco_lvds_display.dtsi |
In order to add a new LVDS into the above mentioned list, timing structure must be modified to include it.
To obtain the information about the ldb (lvds bridge) 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
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Below is the data timing structure:
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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 an example of ldb structure got for SVGA TFT LCD(800x600 BA104S01-100 ) 10.4 inches (BA104S01-100):panel (datasheet avalaible here).
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name = LBD-SVGA-BA
Clock-frequency = 39600000
Hactive = 800
Vactive = 600
Hback = 45
Hfront = 45
Vback = 25
Vfront = 25
Hsync = 10
Vsync = 10 |
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Please follow the steps below to add the custom display timing data into the arch/arm/boot/dts/imx6qdl-seco_lvds_display.dtsi
2. U-Boot: Adding Custom LVDS resolution into list
The resolution 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, please follow the steps described below:
The target file to be edited is u-boot-seco/cmd/cmd_seco_config.c. This one contains the list of available LVDS resolutions to pass to kernel via bootargs (selection is performed via seco_config command).
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cd linuxu-boot-seco/arch/arm/bootcmd/dts vi imx6qdl-cmd_seco_lvds_displayconfig.dtsic |
Now add the newly created ldb structure into the LVDS device tree file and save the file.Once the setup is done, you can compile the source.
| Info |
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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. |
U-Boot: Adding Custom LVDS resolution into list
The resolution 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 performed via seco_config command.
Add the custom resolution setting with a new item into the follow structure:
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Add the custom resolution settings by appending new items into the following structure:
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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:
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Field
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Description
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DISPLAY NAME
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The fields <DISPLAY NAME>, <KERNEL DISPLAY NAME>, <PIXEL FORMAT>, <DATA MAPPING>, "LDB SETTING", <CHANNEL NUMBER> are described in the table below:
Field | Description | ||
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DISPLAY NAME | Name shown into the resolution list when seco_config command is used | ||
KERNEL DISPLAY NAME | name Name of the resolution added into the kernel file arch/arm/boot/dts/imx6qdl-seco_lvds_display.dtsi ($name variable) | ||
PIXEL FORMAT | splay Display interface pixel format as below:
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DATA MAPPING | color 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 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:
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3. U-Boot: Adding Custom LVDS resolution for Splash Screen
Also the U-Boot uses the Display to display the Splash Screen. So, if the scope is to use also the custom resolution at U-Boot level, this task have to be performed:
Editing the file board/seco/common/display.c
A new node into struct display_info_t const displays[] must to be added.
Starting from the above structure (data timings structure), edit the sub-structure "mode" by considering the following fields:
Field | Description |
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name | name of the resolution, to use at U-Boot level |
refresh | refrash rate of the panel (pixecl clock / [ ( tot horiz. pixel) * (tot vert. pixel) ] |
xres | horizontal active area |
yres | vertical active area |
pixclock | pixel clock in pico seconds |
left_margin | horizontal back porch |
right_margin | horizontal fromt porch |
upper_margin | vertical back porch |
lower_margin | vertical fromt porch |
hsync_len | horizontal SYNC |
vsync_len | vertical SYNC |
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}, { .bus = -1, .addr = -1, .pixfmt = IPU_PIX_FMT_RGB24, .detect = NULL, .enable = enable_lvds, |
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.mode = { // Rif. Panel 1024x768 Panel UMSH-8596MD-15T |
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.name = "LDB-1280P60", .refresh = 60, .xres = 1280, |
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.yres = 800, .pixclock = 15128, .left_margin = 220, |
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.right_margin = 40, .upper_margin = 21, .lower_margin = 7, .hsync_len = 60, |
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The board has now successfully been loaded with LVDS and Touch (st1232) dtbo file. |
U-Boot: Adding Custom LVDS resolution for Splash Screen
Also the U-Boot uses the Display to display the Splash Screen. So, if the scope is to use also the custom resolution also at U-Boot level, this task have to be performed:
Editing the file board/seco/common/display.c
A new node into “struct display_info_t const displays[]” must to be added. Under the sub-structure
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.vsync_len = 10, .sync = 0, .vmode = FB_VMODE_NONINTERLACED } }, { .bus = -1, .addr = -1, |
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.pixfmt = |
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IPU_PIX_FMT_RGB24, .detect = NULL, |
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.enable = |
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enable_lvds, .mode = { |
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// new data structure |
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.name |
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= "NEW CUSTOM RESOLUTION", |
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.refresh = <custom refresh>, |
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.xres = <custom horiz. resolution>, |
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.yres |
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= <custom vert. resolution>, . |
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pixclock |
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<pixel clock in us>, .left_margin = <horiz. |
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back porch>, |
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.right_margin = <horiz. front porch>, |
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.upper_margin = <vert. back |
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porch>, .lower_margin = |
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<vert. |
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front porch>, |
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.hsync_len = <horiz. SYNC lenght>, |
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.vsync_len = <vert. SYNC lenght>, |
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.sync = 0, |
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.vmode = FB_VMODE_NONINTERLACED |
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} |
4. Boot with new resolution
Set the right resolution at U-Boot:
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setenv panel "<resolution name>
saveen |
Set the right resolution at kernel, using
seco_configcommand:
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MX6QDLS SBC-A62 U-Boot > seco_config ... __________________________________________________ = 60, Chose Video .vsync_len = 10, .sync = 0,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 .vmode = FB_VMODE_NONINTERLACED } }, |
Insert the new custom resolution, starting from the one above and edit the sub-structure "mode", considering the following fields:
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Field
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Description
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name
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name of the resolution, to use at U-Boot level
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refresh
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refrash rate of the panel (pixecl clock / [ ( tot horiz. pixel) * (tot vert. pixel) ]
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xres
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horizontal active area
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yres
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vertical active area
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pixclock
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pixel clock in pico seconds
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left_margin
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horizontal back porch
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right_margin
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horizontal fromt porch
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upper_margin
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vertical back porch
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lower_margin
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vertical fromt porch
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hsync_len
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horizontal SYNC
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vsync_len
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vertical SYNC
To select the right display resolution at run time, set the "panel" variable according to the associated name into structure above:
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setenv panel "<resolution name> saveenfor LVDS1. __________________________________________________ 1) WVGA [800x480] 2) SVGA [800x600] 3) XGA [1024x768] 4) WXGA [1368x768] 5) WXGAP60 [1280x800] 6) SXGA [1280x1024] 7) HD1080 [1920x1080] 8) NEW_RESOLUTION > 8 ... Saving Environment to MMC... Writing to MMC(1)... OK |
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The board has now successfully been loaded with new custom LVDS resolution |
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Display Customization Guide for i.MX8
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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.
Adding Custom LVDS / eDP panel support in panel-simple.c for i.MX8
The panel is configured by the following nodes located in the board device tree, for example arch/arm64/boot/dts/seco/seco-imx8mm-c61.dts:
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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 through the compatibleproperty to an existing or newly added panel from the panel-simple driver.
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linux-seco/drivers/gpu/drm/panel/panel-simple.c |
Example: Configure the custom display timing for AUO Panel model p215hca
In the Seco SECO BSP's the references panels are configured and tested with 10000 on/off cycle. Below is the panel structure from drivers/gpu/drm/panel/panel-simple.c for LVDS 1920x1080 from Seco SECO BSP9:
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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 . All the parameters configured in struct display_timing are derived from the panel datasheet.
After setup setting up the panel configuration, you need to check for LVDS the following file for the LVDS (for the eDP this part section can be skipped):
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linux-seco/arch/arm64/boot/dts/seco/overlays/seco-imx8mm-c61-lcdif-sn65dsi84-overlay.dts |
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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 the bridge configuration, it is necessary to correctly configure the following parameters:
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The above configurations can be useless in some cases and prevent the panel from turning 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
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u-boot seco c61=> 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-imx8mm-c61.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-c61-lcdif-sn65dsi86.dtbo 3) LVDS LCDIF-1920x1080 - seco-imx8mm-c61-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 The board will boot with your display configuration.
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