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IMX6 IPU Display Clock Configuration Help

ranaya , 01-10-2017, 07:07 PM
Hi All,
I am having a trouble setting up the the clock rate of IPU1DI0 of IMX6Q. Currently the parent clock of IPU1DI0 is set to PLL5_vid_dev (76MHz), and the clock divider being 2 (38MHz) according to clock summary result. I want to bring this IPU clock rate to a lower value (to interface with a low resolution LCD - pxclk of 27MHz), by increasing the clock divider. I am aware that the relevant value should be written to CCM_CHSCCDR (base+0x34) as per IMX6QRM, but where do I need to make the changes (in U-boot or kernel and what are the source files) ?

There is this parent clock assignment line in clk-imx6q.c :
clk[IMX6QDL_CLK_IPU1_DI0_PRE] = imx_clk_divider(“ipu1_di0_pre”, “ipu1_di0_pre_sel”, base + 0x34, 3, 3);

imx_clk_set_parent(clk[IMX6QDL_CLK_IPU1_DI0_PRE_SEL], clk[IMX6QDL_CLK_PLL5_VIDEO_DIV]);
imx_clk_set_parent(clk[IMX6QDL_CLK_IPU1_DI0_SEL], clk[IMX6QDL_CLK_IPU1_DI0_PRE]);

If I'm not mistaken, the imx_clk_divider should return the divider value. But here how the divisor is determined ? I don't want to change the parent clock, but to change the clock divider to 3 ! Specifically what do 3, 3 parameters passed into imx_clk_divider() mean ?

Thanks in Advance
robertferanec , 01-11-2017, 11:45 AM
It will depend on what software you are using, but here is an example how we changed clock in Kernel 3.0.35. Maybe it will help you (check out the arch/arm/mach-mx6/clock.c): https://github.com/FEDEVEL/imx6rex-l...7671698d88197d
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