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AM572x custom LCD

Michel Catudal
Genius 3825 points

Other Parts Discussed in Thread: AM5728

I am trying to figure out what values to change to get the LCD from US Micro to work.

Here is the setup in am57xx-evm-common.dtsi for the 7 inch display. I removed the supply control since it is not used and the gpio to turn it on as it is always on.

       lcd0: display {
                compatible = "osddisplays,osd070t1718-19ts", "panel-dpi";

                label = "lcd";


                panel-timing {
                        clock-frequency = <33000000>;
                        hactive = <800>;
                        vactive = <480>;
                        hfront-porch = <210>;
                        hback-porch = <16>;  
                        hsync-len = <30>;    
                        vback-porch = <10>;  
                        vfront-porch = <22>;
                        vsync-len = <13>;    
                        hsync-active = <0>;  
                        vsync-active = <0>;  
                        de-active = <1>;   
                        pixelclk-active = <1>;
                };

                port {
                        lcd_in: endpoint {
                                remote-endpoint = <&dpi_out>;
                        };
                };
        };

        backlight {
                compatible = "pwm-backlight";
                pwms = <&ehrpwm1 0 50000 0>;

                /* Anything lower than 241 is no longer visible */
                brightness-levels = <0 243 245 247 249 251 252 253 255>;

                default-brightness-level = <8>;
        };

The LCD display is LVDS and we use THCC63LVD823B device to convert to LVDS

Resolution is 1920x720


How do I calculate the other values and what should I put in the compatible section.

For the backlight on the schematic it shows ehrpwm2A but here it says ehrpwm1, I am not sure how to interpret this one.

We did connect the backlight to the same one as on the 7 inch.

Michel

  • 0
    Genius 3825 points
    I have too many C in the part. It is THC63LVD823B

    Michel
  • 0 in reply to Michel Catudal
    TI__Guru**** 393215 points
    The software team have been notified. They will respond here.
  • 0
    TI__Guru*** 125430 points

    Michel Catudal said:
           lcd0: display {
                    compatible = "osddisplays,osd070t1718-19ts", "panel-dpi";

    The important one there is panel-dpi.  It is documented at <linux>/Documentation/devicetree/bindings/display/panel/panel-dpi.txt.  The other one is just informational as far as I can tell.  I assume it's in the compatible field rather than just a comment so that it can be observed easily at run-time (i.e. through <targetfs>/proc/device-tree/display/compatible).

    Michel Catudal said:
    How do I calculate the other values and what should I put in the compatible section.

    You will need to work with your display vendor and/or MIPI bridge vendor to determine the appropriate timings.

    Michel Catudal said:
    For the backlight on the schematic it shows ehrpwm2A but here it says ehrpwm1, I am not sure how to interpret this one.

    The hardware numbers these subsystems 1,2,3 but the dra7.dtsi file names them 0,1,2.  Unfortunately it would cause such a disruption to change the definitions at this point, that it's likely to stick around indefinitely.

  • 0 in reply to Brad Griffis
    Genius 3825 points
    I have a strange issue with our 12 inch LCD.
    It is an LVDS display 1920x720

    It is connected to the am5728 evm board using a THC63LVD823B device.
    It works perfectly on the command line, except for the cursor bug also present on the TI 7 inch board.
    The cursor goes to the top when you reach the bottom of the screen. I had mentioned that bug to TI but nothing came out of it. Anyhow that is not what concerns me at the moment.

    When I load the weston desktop I only see about a 1/8 of the vertical display, Horizontally I get all pixels
    It becomes a 1920x90 display. When I go back to the command line with ctrl F1, it is perfect display.

    Do you have any clue at to what is happening with Weston. This is using the very latest SDK as of early November.

    It works without issue with the HDMI display.

    Here is a part of the devicetree

    aliases {
    display0 = &lcd0;
    };

    lcd0: display {

    status = "okay";
    compatible = "", "panel-dpi";

    label = "lcd";

    panel-timing {
    clock-frequency = <93688800>;
    hactive = <1920>;
    vactive = <720>;
    hfront-porch = <115>;
    hback-porch = <20>;
    hsync-len = <5>;
    vback-porch = <3>;
    vfront-porch = <32>;
    vsync-len = <3>;
    hsync-active = <0>;
    vsync-active = <0>;
    de-active = <1>;
    pixelclk-active = <1>;
    };

    port {
    lcd_in: endpoint {
    remote-endpoint = <&dpi_out>;
    };
    };
    };

    backlight {
    status = "okay";
    compatible = "pwm-backlight";
    pwms = <&ehrpwm1 0 22000 0>;
    pwm-names = "LCD";

    enable-gpios = <&gpio6 11 GPIO_ACTIVE_HIGH>;

    /* Anything lower than 241 is no longer visible */
    brightness-levels = <0 243 245 247 249 251 252 253 255>;

    default-brightness-level = <8>;
    };




    Michel
  • 0 in reply to Michel Catudal
    Genius 3825 points
    One interesting observation, when I shut the app down (crtrl C from ssh) I see a full screen with correct picture for a few seconds.
    Moving the mouse will refresh the screen.

    Michel