Porting LVDS LCD With Low Resolution to i.MX6

Document created by Wigros Sun Employee on Aug 17, 2015Last modified by Wigros Sun Employee on Aug 18, 2015
Version 3Show Document
  • View in full screen mode

Some customers often use LVDS LCD with low resolution on i.MX6 platform, such as 320x240, but by defualt , linux bsp doesn't support low frequency pixel clock for LVDS module input.


    When we port LVDS LCD with 320x240 resolution to android4.2.2, we found pixel clock is not correct, it always output 38.9MHz, it is no probem for big resolution , for example 1024x768, but the clock we need for 320x240 LCD is 6.4MHz.

    According to the quesiton, Let us check IPU & LDB clock in i.MX6 datasheet at first :






From above table, if ldb clock is from IPU, we will not get 6.4MHz pixel clock, so we will have to adjust its source clock:


The following steps are procedure that ports LVDS LCD with 320x240 resolution to i.MX6Q.

1. Adding LVDS LCD timing structure to ldb.c

static struct fb_videomode ldb_modedb[] = {
      "LDB-XGA", 60, 320, 240, 155914,
      38, 20,
      15, 4,
      30, 3,



     "LDB-1080P60", 60, 1920, 1080, 7692,

     100, 40,

     30, 3,

     10, 2,





2.Modifying clock source of ldb module

Checking /arch/arm/mach-mx6/clock.c, we can find there are 3 ldb's clock source : &pll5_video_main_clk, &pll2_pfd_352M, &pll2_pfd_400M,

static int _clk_ldb_di1_set_parent(struct clk *clk, struct clk *parent)


       u32 reg, mux;

       int rev = mx6q_revision();


       reg = __raw_readl(MXC_CCM_CS2CDR)

              & ~MXC_CCM_CS2CDR_LDB_DI1_CLK_SEL_MASK;


       mux = _get_mux6(parent, &pll5_video_main_clk,

              &pll2_pfd_352M, &pll2_pfd_400M,

              (rev == IMX_CHIP_REVISION_1_0) ?

               &pll3_pfd_540M :       /* MX6Q TO1.0 */

               &mmdc_ch1_axi_clk[0],     /* MX6Q TO1.1 and MX6DL */

              &pll3_usb_otg_main_clk, NULL);

       reg |= (mux << MXC_CCM_CS2CDR_LDB_DI1_CLK_SEL_OFFSET);


       __raw_writel(reg, MXC_CCM_CS2CDR);


       return 0;



By default, pll2_pfd_352M is configured as the clock source of ldb:

clk_set_parent(&ldb_di0_clk, &pll2_pfd_352M);

       clk_set_parent(&ldb_di1_clk, &pll2_pfd_352M);

We should change the clock source to be pll5_video_main_clk

clk_set_parent(&ldb_di0_clk, &pll5_video_main_clk,);

       clk_set_parent(&ldb_di1_clk, &pll5_video_main_clk,);

3. Configuring initial clock in board-mx6q_sabresd.c

static struct ipuv3_fb_platform_data sabresd_fb_data[] = {

       { /*fb0*/

       .disp_dev = "ldb",

       .interface_pix_fmt = IPU_PIX_FMT_RGB666,

       .mode_str = "LDB-XGA",

       .default_bpp = 16,

       .int_clk = false,

       .late_init = false,


int_clk=false means LDB clock is from PLL2_PFD_352 or pll5_video_main_clk; int_clk=true mean LDB clock if from IPU.



OK, after doing above steps, LVDS LCD with low resolution should normally work.



Freescale TICS team



2 people found this helpful