i.mx6 33.26MHz LVDS panel cannot display in u-boot

[jerrylain]

Hi,

I'm trying to porting a panel on i.mx6dl which is LB070WV8-SL02. Typical DCLK is 33.26MHz. I'm trying to set .pixclock to 30066, then measure LVDS1_CLK_P/LVDS1_CLK_N which output is 33.26MHz. But it only has backlight without any data, if I modify .pixclock to 22222, which output clock will be 45MHz. Then display will be normal. But from spec, frequency should between 31.95MHz~34.60MHz.

Because I also use 33.26MHz in kernel, and display does not have any problems. So suspect it should be uboot code problems, but don't have any ideas.

Try to compare below related registers in u-boot between 33MHz and 45MHz, it seems nothing special.

a. IPU related registers.

b. LDB register

c. CCM registers <-- only different are CCM_ANALOG_PLL_VIDEO_NUM and CCM_ANALOG_PLL_VIDEO because set different clock.

Below is panel table.

.bus = -1,
.addr = 0,
.pixfmt = IPU_PIX_FMT_RGB24,
.detect = NULL,
.enable = enable_lvds,
.mode = {
   .name = "LG-LB070WV8",
   .refresh = 60,
   .xres = 800,
   .yres = 480,
   .pixclock = 30066,
   .left_margin = 100,
   .right_margin = 100,
   .upper_margin = 20,
   .lower_margin = 20,
   .hsync_len = 56,
   .vsync_len = 5,
   .sync = FB_SYNC_EXT,
   .vmode = FB_VMODE_NONINTERLACED

   }

u-boot version is U-Boot 2015.04-gd239e2d, which does not enable PLL5 clock, so we try to enable PLL5 clock by ourselves and it seems workable.

kernel version is 3.14.52.

If anyone has any suggestions, that will be very helpful. Thanks in advance.

[jerrylain · Accepted solution]

Thanks for reply. Actually, I have solved this issue.

First of all, the error happens at 

clk_set_rate(g_pixel_clk[disp], rounded_pixel_clk);

in ipu_disp.c

Above will use g_pixel_clk set_rate function to set clock rate which approach panel pixel rate we defined in display structure. In set_rate function, it will use g_pixel_clk parent, which is g_ldb_clk as a divider to calculate. After calculate, it will set DI_BS_CLKGEN0 and DI_BS_CLKGEN1 register to let IPU pixel clock sync with LDB clock. But g_ldb_clock has been always set to 65MHz, that means a lot of clock rate cannot be divide, then IPU pixel clock will not sync with LDB clock, so display cannot output anything.

As I know, g_pixel_clk which should use same clock parent as ldb clock. That is what kernel did.

So for short term, just modify g_ldb_clock.rate to same as your ldb clock rate, then ipu_pixel_clk_set_rate can divide clock rate correctly.

[joanxie]

pls refer to the document as below:

https://community.nxp.com/docs/DOC-172312?sr=search&searchId=30afbc13-c544-4fa5-bdce-e7eb986cc3c1&se... 

hope helpful for you