Two LVDS channels in separate mode on i.MX6Q running Linux v3.14

[HectorPalacios]

Hello,

I'm running Freescale's BSP for Linux kernel v3.14 (branch imx_3.14.28_1.0.0_ga) and wanted to have two LVDS channels in separate mode:

IPU1:DI0 --> LVDS0

IPU1:DI1 --> LVDS1

I have my LVDS display working if I only enable one channel, either LVDS0 or LVDS1.

I also have dual display working if I enable both channels and use the property dual-mode, thus having cloned image on LVDS0 and LVDS1.

However, if I enable both LVDS channels in separate mode (without either property dual-mode or split-mode the kernel hangs.

My device tree (omitting some data) looks like:

&ldb {
    lvds-channel@0 {
        crtc = "ipu1-di0";
        status = "okay";
        primary;
    };
    lvds-channel@1 {
        crtc = "ipu1-di1";
        status = "okay";
    };
};

The kernel hangs around the fb_set_var() call in this piece of code in the function mxcfb_register() of mxc_ipuv3_fb.c driver:

if (!mxcfbi->late_init) {
    fbi->var.activate |= FB_ACTIVATE_FORCE;
    console_lock();
    fbi->flags |= FBINFO_MISC_USEREVENT;
    ret = fb_set_var(fbi, &fbi->var);
    fbi->flags &= ~FBINFO_MISC_USEREVENT;
    console_unlock();
    if (ret < 0) {
        dev_err(fbi->device, "Error fb_set_var ret:%d\n", ret);
        goto err3;
    }
    ...

Has anybody tested LVDS0 and LVDS1 in separate mode?

[alejandrolozan1]

Hi,

Which modifications did you perform to configure both LVDS in separate mode?

Best Regards,

Alejnadro

[HectorPalacios]

Hi,

I didn't do any modification than what the Device Tree I posted. By not having either the 'dual-mode' or 'spli-mode' boolean properties and having the 'crtc' property on each LVDS channel to a different DI, I expect the driver is able to route a different framebuffer to each LVDS channel.

Here are my framebuffers linked to ldb display:

	mxcfb2: fb@1 {
	compatible = "fsl,mxc_sdc_fb";
	disp_dev = "ldb";
	interface_pix_fmt = "RGB666";
	default_bpp = <16>;
	int_clk = <0>;
	late_init = <0>;
	status = "okay";

    };

    mxcfb4: fb@3 {

	compatible = "fsl,mxc_sdc_fb";
	disp_dev = "ldb";
	interface_pix_fmt = "RGB666";
	default_bpp = <16>;
	int_clk = <0>;
	late_init = <0>;
	status = "okay";

    };

Has Freescale tested separate dual display with LDB?

Thank you.

[alejandrolozan1 · Accepted solution]

Hi Héctor,

Below is what I was answered back from the experts:

The default 3.14.28 GA BSP can support separate mode directly, you just need set the video mode in kernel command line as followed:

video=mxcfb0:dev=ldb,LDB-XGA,if=RGB666 video=mxcfb1:dev=ldb,LDB-XGA,if=RGB666 video=mxcfb2:off video=mxcfb3:off

For iMX6Q SabreSD, arch/arm/boot/dts/imx6q-sabresd.dts, the default is:

&ldb {
lvds-channel@0 {
  crtc = "ipu2-di0";
};

lvds-channel@1 {
  crtc = "ipu2-di1";
};
};

You can change them to followed for IPU1:

&ldb {
lvds-channel@0 {
  crtc = "ipu1-di0";
};

lvds-channel@1 {
  crtc = "ipu1-di1";
};
};

After booted, you can use "echo 0 > /sys/class/graphics/fb2/blank" to enable the second LVDS display, then you can use the memtool to check the setting from registers:

/unit_tests/memtool -32 0x020e0008 1    (LDB_CTRL)

/unit_tests/memtool -32 0x020e000c 1    (IOMUXC_GPR3, LVDSx_MUX_CTL)

/Alejandro

[HectorPalacios]

Hi Alejandro,

The kernel hang was due to a wrong patch I had on ldb.c driver. After fixing it, separate mode worked fine. Thanks.