Changes between Version 8 and Version 9 of ventana/LVDS


Ignore:
Timestamp:
07/17/2019 10:46:35 PM (5 months ago)
Author:
Bobby Jones
Comment:

Add backlight troubleshooting section

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  • ventana/LVDS

    v8 v9  
    152152 * touchscreen's are typically I2C or USB based devices with drivers in the {{{drivers/input/touchscreen}}} directory
    153153
    154 
    155154[=#troubleshooting]
     155=== Troubleshooting Backlight Portion ===
     156In some cases the device tree node used by the linux {{{pwm-backlight}}} driver may need to be adjusted if
     157"flickering" exists ([https://i.stack.imgur.com/LF3Y4.jpg example]). This phenomenon is caused by a pwm frequency setting that is too low for the connected display's backlight which creates a visual artifact that may be detectable by the human eye.
     158
     159As described in the pwm device tree bindings [https://raw.githubusercontent.com/torvalds/linux/master/Documentation/devicetree/bindings/pwm/pwm.txt documentation], the backlight node of the device tree has a property labelled {{{pwms}}}. This property has includes the {{{pwm-specifier}}} which typically encodes the chip-relative PWM number and the PWM
     160period in nanoseconds.
     161{{{
     162backlight {
     163        compatible = "pwm-backlight";
     164        pwms = <&pwm1 0 5000000>;               /* 1 / (5000000 / 1000000000) = 200 Hz */
     165        brightness-levels = <
     166                0  1  2  3  4  5  6  7  8  9
     167                10 11 12 13 14 15 16 17 18 19
     168                20 21 22 23 24 25 26 27 28 29
     169                30 31 32 33 34 35 36 37 38 39
     170                40 41 42 43 44 45 46 47 48 49
     171                50 51 52 53 54 55 56 57 58 59
     172                60 61 62 63 64 65 66 67 68 69
     173                70 71 72 73 74 75 76 77 78 79
     174                80 81 82 83 84 85 86 87 88 89
     175                90 91 92 93 94 95 96 97 98 99
     176                100
     177                >;
     178        default-brightness-level = <100>;
     179};
     180}}}
     181
     182If you want to make an adjustment to this frequency, you can use the {{{fixfdt}}} script in the bootloader. For example, to change the backlight frequency to {{{10kHz}}} you would run the following command from the bootloader:
     183{{{#!bash
     184# The third value of the pwms property is in nanoseconds so to convert to Hz:
     185# 1 / (100000 / 1000000000) = 10 kHz
     186setenv fixfdt "fdt addr ${fdt_addr}; fdt set /backlight pwms <0x3d 0 100000>"
     187}}}
     188
    156189=== Troubleshooting Touchscreen Portion ===
    157190There is a command line tool called {{{evtest}}} that can be used to check for touch events.