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i.MX6Q LVDS Wrong clock issue

Question asked by Ettore Chimenti on May 17, 2015
Latest reply on Oct 8, 2015 by Laszlo Timko

Hi all,

 

I have a custom iMX6q derived from SABRE and I wanted to use a 7 inches 800x480 WVGA monitor attached to the LVDS channel 0.

The monitor works with an operating clock freq at 33.26 MHz, but it works well even with 38MHz (tested).

 

I'm using kernel 3.14.28_ga, I've modified the original SABRE DTS specifing:

        mxcfb1: fb@0 {
            compatible = "fsl,mxc_sdc_fb";
            disp_dev = "ldb";
            interface_pix_fmt = "RGB666";
            mode_str ="LDB-WVGA";
            default_bpp = <32>;
            int_clk = <0>;
            late_init = <0>;
            status = "okay";
        };

 

&ldb {
    status = "okay";
    primary;
    
    lvds-channel@0 {
        reg = <0>;
        fsl,data-mapping = "spwg";
        fsl,data-width = <18>;
        status = "okay";
        crtc = "ipu1-di0";
        display-timings {
            native-mode = <&timing1>;
            timing1: 800x480 {
                clock-frequency = <38000000>;
                hactive = <800>;
                vactive = <480>;
                hback-porch = <56>;
                hfront-porch = <50>;
                vback-porch = <23>;
                vfront-porch = <20>;
                hsync-len = <150>;
                vsync-len = <2>;
            };
        };
    };
};

 

From dmesg output:

 

mxc_sdc_fb fb.18: registered mxc display driver ldb
Console: switching to colour frame buffer device 100x30

 

The LVDS manages to light up, but remains blank.

Testing with an oscilloscope it seems the clock output is giving 76MHz instead!

 

How can I set the right clock frequency?

 

Any ideas?

 

- ec

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