Messages in this thread | | | From | Fabio Estevam <> | Date | Tue, 6 Jun 2023 15:45:15 -0300 | Subject | Re: [PATCH] clk: imx: composite-8m: Add imx8m_divider_determine_rate |
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On Sat, May 6, 2023 at 4:53 PM Adam Ford <aford173@gmail.com> wrote: > > Currently, certain clocks are derrived as a divider from their > parent clock. For some clocks, even when CLK_SET_RATE_PARENT > is set, the parent clock is not properly set which can lead > to some relatively inaccurate clock values. > > Unlike imx/clk-composite-93 and imx/clk-divider-gate, it > cannot rely on calling a standard determine_rate function, > because the 8m composite clocks have a pre-divider and > post-divider. Because of this, a custom determine_rate > function is necessary to determine the maximum clock > division which is equivalent to pre-divider * the > post-divider. > > With this added, the system can attempt to adjust the parent rate > when the proper flags are set which can lead to a more precise clock > value. > > On the imx8mplus, no clock changes are present. > On the Mini and Nano, this can help achieve more accurate > lcdif clocks. When trying to get a pixel clock of 31.500MHz > on an imx8m Nano, the clocks divided the 594MHz down, but > left the parent rate untouched which caused a calulation error. > > Before: > video_pll 594000000 > video_pll_bypass 594000000 > video_pll_out 594000000 > disp_pixel 31263158 > disp_pixel_clk 31263158 > > Variance = -236842 Hz > > After this patch: > video_pll 31500000 > video_pll_bypass 31500000 > video_pll_out 31500000 > disp_pixel 31500000 > disp_pixel_clk 31500000 > > Variance = 0 Hz > > All other clocks rates and parent were the same. > Similar results on imx8mm were found. > > Fixes: 690dccc4a0bf ("Revert "clk: imx: composite-8m: Add support to determine_rate"") > Signed-off-by: Adam Ford <aford173@gmail.com>
This works fine on my imx8mm-evk, so:
Tested-by: Fabio Estevam <festevam@gmail.com>
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