The aim of this section is to properly configure custom display: LVDS and eDP panels.
| Table of Contents |
|---|
Standard Display Timings
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
...
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.
LVDS Customization Guide for i.MX6
In order to bring up custom display following steps are needed:
1. Kernel: Adding Custom LVDS support in Device tree file
The target file to edit is linux-seco/arch/arm/boot/dts/imx6qdl-seco_lvds_display.dtsi. This last contains the list of available LVDS resolutions.
| Code Block |
|---|
cd linux-seco/arch/arm/boot/dts
vi imx6qdl-seco_lvds_display.dtsi |
A newest one have to be enclosed into “timing” structure.
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
Is this the struct you were talking about?
| Code Block |
|---|
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 an example of lbd structure got for SVGA TFT LCD(800x600) 10.4 inches panel (datasheet avalaible here) is the sample timing data for SVGA TFT LCD(800x600) 10.4 inches (BA104S01-100):
...
The aim of this section is to properly configure custom display: LVDS and eDP panels.
| Table of Contents |
|---|
| Info |
|---|
External references are available here: |
...
Standard Display Timings
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 | 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. |
...
LVDS Customization Guide for i.MX6
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.
| Code Block |
|---|
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
Below is the data timing structure:
| Code Block |
|---|
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 an example of ldb structure got for SVGA TFT LCD(800x600 BA104S01-100 ) 10.4 inches panel (datasheet avalaible here).
...
| Code Block |
|---|
name = LBD-SVGA-BA Clock-frequency = 39600000 Hactive = 800 Vactive = 600 Hback = 45 Hfront = 45 |
...
Vback = 25 |
...
|
...
Vfront = |
...
25 |
...
Hsync = |
...
10 |
...
Vsync = 10 |
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).
| Code Block |
|---|
cd u-boot-seco/cmd/
vi cmd_seco_config.c |
Add the custom resolution settings by appending new items into the following structure:
| Code Block | ||
|---|---|---|
| ||
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", "", Hfront = 451 }, { "WXGA [1368x768]", "LDB-WXGA", "RGB24", Vback = 25 "datamap=jeida", "", 1 }, { "WXGAP60 [1280x800]", Vfront = 25 "LDB-1280P60", "RGB24,bpp=32","datamap=spwg", "", 1 }, { "SXGA [1280x1024]", "LDB-SXGA", Hsync ="RGB24", 10 "datamap=jeida", "", 1 }, { Vsync = 10 |
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 steps below described:
The target file to edit is u-boot-seco/cmd/cmd_seco_config.c. This last contains the list of available LVDS resolutions to pass to kernel via bootargs (selection is performed via seco_config command).
| Code Block |
|---|
cd u-boot-seco/cmd/
vi cmd_seco_config.c |
Add the custom resolution settings by appending new items into the following structure:
| Code Block | ||
|---|---|---|
| ||
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>}
}; |
The fields <DISPLAY NAME>, <KERNEL DISPLAY NAME>, <PIXEL FORMAT>, <DATA MAPPING>, "LDB SETTING", <CHANNEL NUMBER> are here described:
...
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 ($name variable)
...
PIXEL FORMAT
Display interface pixel format:
...
"HD1080 [1920x1080]", "LDB-1080P60", "RGB24", "datamap=spwg", "ldb=spl0", 2 },
{<DISPLAY NAME>, <KERNEL DISPLAY NAME>, <PIXEL FORMAT>, <DATA MAPPING>, "LDB SETTING", <CHANNEL NUMBER>}
}; |
The fields <DISPLAY NAME>, <KERNEL DISPLAY NAME>, <PIXEL FORMAT>, <DATA MAPPING>, "LDB SETTING", <CHANNEL NUMBER> are described in the table below:
Field | Description | ||
|---|---|---|---|
DISPLAY NAME | Name shown into the resolution list when seco_config command is used | ||
KERNEL DISPLAY NAME | Name of the resolution added into the kernel file arch/arm/boot/dts/imx6qdl-seco_lvds_display.dtsi ($name variable) | ||
PIXEL FORMAT | Display interface pixel format:
| ||
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) |
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 |
|---|---|
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 |
| Code Block |
|---|
}, { .bus = -1, .addr = -1, .pixfmt = IPU_PIX_FMT_ |
...
RGB24, |
...
.detect = NULL, |
...
|
...
.enable = enable_lvds, |
...
.mode = { |
...
|
...
// Rif. |
...
Panel 1024x768 Panel UMSH-8596MD-15T |
...
|
...
|
...
.name |
...
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)
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. Under the sub-structure
...
= "LDB-1280P60", .refresh = 60, .xres = 1280, .yres = 800, .pixclock = 15128, |
...
. |
...
left_margin = |
...
220, . |
...
right_margin = |
...
40, . |
...
upper_margin = |
...
21, . |
...
lower_margin = |
...
7, . |
...
hsync_len |
...
|
...
= 60, |
...
|
...
|
...
.vsync_len = 10, |
...
.sync |
...
|
...
|
...
|
...
= 0, . |
...
vmode |
...
= |
...
FB_VMODE_NONINTERLACED } }, { |
...
. |
...
bus |
...
= |
...
-1, .addr = -1, .pixfmt = |
...
IPU_PIX_FMT_RGB24, .detect |
...
= |
...
NULL, .enable = enable_lvds, .mode = { |
...
|
...
|
...
// new data structure . |
...
name |
...
|
...
= "NEW CUSTOM RESOLUTION", .refresh |
...
= <custom |
...
refresh>, .xres |
...
= |
...
<custom horiz. resolution>, .yres |
...
= |
...
<custom vert. resolution>, . |
...
pixclock |
...
|
...
= <pixel clock in us>, |
...
. |
...
left_ |
...
margin = <horiz. |
...
back |
...
porch>, |
...
.right_margin = <horiz. front |
...
porch>, .upper_margin = <vert. back porch>, |
...
|
...
|
...
.lower_margin = <vert. front porch>, . |
...
hsync_len = <horiz. |
...
SYNC lenght>, |
...
.vsync_len = <vert. SYNC |
...
Insert the new custom resolution, starting from the one above and edit the sub-structure "mode", 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
...
lenght>,
.sync = 0,
.vmode = FB_VMODE_NONINTERLACED
} |
4. Boot with new resolution
Set the right resolution at U-Boot:
| Code Block |
|---|
setenv panel "<resolution name> saveen |
Set the right resolution at kernel, using
seco_configcommand:
| Code Block |
|---|
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]
8) NEW_RESOLUTION
> 8
...
Saving Environment to MMC... Writing to MMC(1)... OK |
| Tip |
|---|
The board has now successfully been loaded with new custom LVDS resolution |
...
Display Customization Guide for i.MX8
...
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:
| Code Block |
|---|
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.
| Code Block |
|---|
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:
| Code Block |
|---|
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):
| Code Block |
|---|
linux-seco/arch/arm64/boot/dts/seco/overlays/seco-imx8mm-c61-lcdif-sn65dsi84-overlay.dts |
...
| Code Block |
|---|
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:
...
| Note |
|---|
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
...