IMX6 LVDS configuration in u-boot

[AntoineP]

Hi,

I have been struggling to set the LDB clock accordingly to my LVDS display in u-boot, to display a splash screen logo. It's a 1920x1200 display with dual channel LVDS interface.

I have defined my display like this, and this works on my devkit (logo displayed in u-boot), but it doesn't on my custom board. The issue is only located in u-boot, the display works well once in the kernel on my custom board (with the same configuration).

struct display_info_t const displays[] = {{

.bus = -1,

.addr = 0,

.pixfmt = IPU_PIX_FMT_RGB24,

.detect = detect_custom_display,

.enable = lvds_enable_disable, /* lvds_enable_disable */

.mode = {

.name = "CUSTOM-WUXGA",

.refresh = 60,

.xres = 1920,

.yres = 1200,

.pixclock = 6488,

.left_margin = 60,

.right_margin = 60,

.upper_margin = 15,

.lower_margin = 15,

.hsync_len = 40,

.vsync_len = 5,

.sync = 0,

.vmode = FB_VMODE_NONINTERLACED

} }, {

It seems to be linked to the LDB clock which is set at 75 MHz, and the clock required for my screen is 154MHz. How can I change the LDB clock to get 150MHz? Default options seem to be in the range 50-75MHz.

/* set LDB0, LDB1 clk select to 011/011 */

reg = readl(&mxc_ccm->cs2cdr);

reg &= ~(MXC_CCM_CS2CDR_LDB_DI0_CLK_SEL_MASK

| MXC_CCM_CS2CDR_LDB_DI1_CLK_SEL_MASK);

/* 1 -> ~50MHz , 2 -> ~56MHz, 3 -> ~75MHz, 4 -> ~68MHz */

reg |= (3 << MXC_CCM_CS2CDR_LDB_DI0_CLK_SEL_OFFSET)

| (3 << MXC_CCM_CS2CDR_LDB_DI1_CLK_SEL_OFFSET);

writel(reg, &mxc_ccm->cs2cdr);

Thanks,

[AldoG]

Hello,

For dual channel example you could refer to the following patch:

https://community.nxp.com/t5/i-MX-Processors/imx6q-and-lvds/m-p/391391#525359

Best regards,
Aldo.

[AntoineP]

I checked at the oscilloscope and the LVDS clock is the same in u-boot and in the kernel, so it's probably not a clock issue. What could be the reason then? The use of a dual channel LVDS instead of a single one?

I use the same timing configuration in u-boot and in the kernel for my screen and it doesn't work in u-boot, but it does once in the kernel. Also, the display works in u-boot on the devkit screen (which is a single channel LVDS).

The issue is definitely linked to the u-boot configuration of the 1920x1200 screen.