The aim of this section is to properly configure custom display: LVDS and eDP panels.
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External references are available here: |
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 | 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
In order to bring up a custom display following steps are needed:, follow the steps below.
1. Kernel: Adding Custom LVDS support in Device tree file
The target file to edit be edited is linux-seco/arch/arm/boot/dts/imx6qdl-seco_lvds_display.dtsi. This last one contains the list of available LVDS resolutions.
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linux-seco/Documentation/devicetree/bindings/display/imx/ldb.txt
linux-seco/Documentation/devicetree/bindings/fb/fsl_ipuv3_fb.txt
Here below 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>;
}; |
Here below Below is an example of ldb structure got for SVGA TFT LCD(800x600 BA104S01-100 ) 10.4 inches panel (datasheet avalaible here).
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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 described:
The target file to edit be edited is u-boot-seco/cmd/cmd_seco_config.c. This last 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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The fields <DISPLAY NAME>, <KERNEL DISPLAY NAME>, <PIXEL FORMAT>, <DATA MAPPING>, "LDB SETTING", <CHANNEL NUMBER> are here described in the table below:
Field | Description | ||
|---|---|---|---|
DISPLAY NAME | Name shown 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 | Display interface pixel format:
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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) |
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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 |
|---|---|
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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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
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__________________________________________________
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]
8) NEW_RESOLUTION
> 8
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Saving Environment to MMC... Writing to MMC(1)... OK |
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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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