Calculation of important parameters for RK3288 EDP debugging
edp-panel {
status = "okay";
reset-delay-ms = <20>;
init-delay-ms = <20>;
enable-delay-ms = <120>;
prepare-delay-ms = <120>;
unprepare-delay-ms = <20>;
display-timings {
timing-edp {
clock-frequency = <143078400>;
hactive = <1920>;
vactive = <1080>;
hfront-porch = <64>;
hsync-len = <16>;
hback-porch = <80>;
vfront-porch = <11>;
vsync-len = <4>;
vback-porch = <16>;
hsync-active = <0>;
vsync-active = <0>;
de-active = <0>;
pixelclk-active = <0>;
};
};
};
Important parameter calculation results in the device tree
clock-frequency= horizontal resolution*vertical resolution*refresh frame rate
For example clock-frequency=1920*1080*60
clock-frequency=143078400
Note : In actual use, it is found that it is generally smaller than the calculated value. If it is too high, the screen will flicker.
device tree
Any writing of the three values of hback-porch , hfront-porch, and hsync-len must satisfy
Calculate according to the type in the above figure
Horizontal Period - Horizontal valid=2080-1920 =160
hback-porch+hfront-porch+hsync-len = Horizontal Period - Horizontal valid
80+64 +16 =160
Any writing of the three values of vback-porch vfront-porch vsync-len must satisfy the following calculation formula
Calculate according to the type in the above figure
Vertical Period - Vertical valid=1111-1080=31
vback-porch + vfront-porch + vsync-len = Vertical Period - Vertical valid
16+11+4=31
Note :
vback-porch and hback-porch generally take a large value, and others are freely allocated, but the above two conditions must be met.
possible problems
1. The backlight is not bright
Main modification: pwms attribute, including "period" and "pwm polarity".
2. No picture
-
Adjust the clock-frequency period
-
shrink hsync-len and vsync-len
3. Boot splash screen
No need to specify: bus-format attribute