imx8mm: how to dynamically change video_pll1?

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imx8mm: how to dynamically change video_pll1?

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adevries
Contributor V

Hello,

I have an imx8m mini that I am trying to make output different HDMI resolutions. The lcdif_pixel clock is sourced from video_pll1, which is currently 594 MHz. However, I want to output at a resolution that uses a 65 MHz pixel clock. When I try to switch to this resolution, I don't get any output, and I think that's because the lcdif_pixel clock is 66 MHz, not 65 MHz. Given the parent clock of 594 MHz, 66 MHz is probably the closest it can get to 65, but why won't video_pll1 simply change from 594 to 650 MHz? The clock rate is defined in the clk-imx8mm.c driver file. Why won't the PLL switch to 650 MHz?

Thanks

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Qmiller
NXP Employee
NXP Employee

How do you change the code for 65Mhz pixel clk?

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adevries
Contributor V

Hi Qmiller,

I have been using the linux modetest utility to test different resolutions. For example, "modetest -M imx-drm -s 35[at]33:1920x1080-60"  outputs a test pattern at 1920x1080 at 60Hz. That needs a pixel clock of 148.5 MHz. However, when I run "modetest -M imx-drm -s 35[at]33:1024x768-60", I don't get any test pattern being output, and the lcdif_pixel clock is 66 MHz instead of 65 MHz.

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