LVDS crtc field and connection to framebuffer

[danmacdonald]

I am working on connecting an LVDS to my project, with no success as of yet. I am a bit lost when it comes to the crtc field in the device tree.

I am working off kernel 3.14.79

I have modified the hummingboard2 device tree's entry for ldb to suit the timings of my display, to look like this: 

/* old mxcfb1 setting for HDMI - POSTED here for clarity */

/* 

mxcfb1: fb@0 {
      compatible = "fsl,mxc_sdc_fb";
      disp_dev = "hdmi";
      interface_pix_fmt = "RGB24";
      mode_str ="1920x1080M@60";
      default_bpp = <32>;
      int_clk = <0>;
      late_init = <0>;
      status = "okay";
};

*/

/* new fb1 setting for LVDS */

&mxcfb1 {
      disp_dev = "ldb";
      interface_pix_fmt = "RGB666";
      default_bpp = <16>;
      int_clk = <0>;
      late_init = <0>;
      mode_str ="1280x720M@60";
      status = "okay";
};

&ldb {
           status = "okay";

           lvds-channel@0 {
                crtc = "ipu1-di0";   // ipu2-di0  has errors in dmesg on boot

                /* Ive observed the following properties in other posts, which I assume

                 * are specific to splitting the LVDS due to larger displays and the limitations of the clock

                 * but I am unsure if its necessary for a singular display */
                ipu_id = <0>;        
                disp_id = <1>;      
                ext_ref = <1>;      
                mode = "sin0";     
                sec_ipu_id = <0>;
                sec_disp_id = <0>;

                status = "okay";

                display-timings {
                          native-mode = <&timing0>;

                          /* overwrite timings for Tianma TM070JDHG30 */
                          timing0: hsd100pxn1 { 
                                     clock-frequency = <75210590>;
                                     hactive = <1280>;
                                     vactive = <720>;
                                     hback-porch = <5>;
                                     hfront-porch = <64>;
                                     vback-porch = <2>;
                                     vfront-porch = <40>;
                                     hsync-len = <69>;

                                     hsync-len = <69>;
                                     vsync-len = <42>;
                            }; // ~timing0
                }; // ~display-timings
        }; //~lvds-channel@0
}; // ~ldb

I've read that the crtc is supposed to point to the IPU device to connect the LVDS to, but I cannot find any documentation on this property, and/or what other supporting nodes need to be configured for this to work. 

as i mentioned in the comment ipu2_di0 provides errors in dmesg (invalid or unspecified crtc), but ipu1_di0 seems to run okay in the dmesg:

[ 0.414411] mxc_sdc_fb fb.32: registered mxc display driver ldb IPU1_DISP0
[ 0.414424] mxc_sdc_fb fb.32: registered mxc display driver ldb

To summarize :

I can't get my LVDS working, and at this point everything I try is a shot in the dark, so my basic questions are:

1) What value should I be putting for the crtc property?

2) What other supporting (device tree or other) configurations are needed to support the crtc property?

3) How does this magically link to a frame buffer? Thus far I've been catting' to the frame buffers to see if theres any changes on my displays, but have yet to have any luck.

Thanks in advance

[danmacdonald · Accepted solution]

For a sense of completion, I was able to get it working!

My problem was a hardware problem. After that was solved and a slight timing adjustment, using boundary device's timing for the Tianma (I'm using the same display, but not their Boundary U-Boot). For those struggling, here is my device tree node:

&ldb {
    status = "okay";
    lvds-channel@0 {
        crtc = "ipu1-di0";
        ipu_id = <0>;
        disp_id = <0>;
        status = "okay";
        fsl,data-width = <24>;
    
        display-timings {
            native-mode = <&timing1>;
            timing1: tianma {
            clock-frequency = <68152388>;
            hactive = <1280>;
            vactive = <800>;
            hback-porch = <5>;
            hfront-porch = <63>;
            vback-porch = <2>;
            vfront-porch = <39>;
            hsync-len = <1>;
            vsync-len = <1>;
            }; //~display-timings
        }; //~display-timings
    };//~lvds-channel
};//~ldb
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[igorpadykov]

Hi Dan

what processor used in the case, as i.MX6DL has only one IPU,

while i.MX6Q - two. For crtc one can look at ldb driver in

linux/drivers/video/fbdev/mxc/ldb.c and description in attached Linux Manual.

Best regards
igor
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[danmacdonald]

igorpadykov Its an i.MXDL. I have discovered there were hardware issues. I am working to resolve those and then will revisit. In the meantime, it may be a silly question, but is it possible to use the same IPU to provide the same data to two displays simultaneously ? i.e. to HDMI and LVDS ?

EDIT:

nevermind. I see all variants support dual displays here.

https://www.solid-run.com/freescale-imx6-family/imx6-som/imx6-som-specifications/ 

[igorpadykov]

Hi Dan

please look at

Best regards
igor