Messages in this thread | | | From | Adam Ford <> | Date | Mon, 12 Jun 2023 11:11:21 -0500 | Subject | Re: [PATCH] clk: imx: composite-8m: Add imx8m_divider_determine_rate |
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On Mon, Jun 12, 2023 at 11:08 AM Maxime Ripard <maxime@cerno.tech> wrote: > > On Sun, Jun 11, 2023 at 12:02:42PM -0500, Adam Ford wrote: > > On Tue, Jun 6, 2023 at 1:45 PM Fabio Estevam <festevam@gmail.com> wrote: > > > > > > 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. > > > > > > > > + Maxime > > > > > > 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> > > > > > > > Peng / Abel, > > > > Any suggestions on how we can move this forward? Looking at the > > clk-composite-8m driver, imx8m_clk_composite_compute_dividers uses the > > max values which is basically what my patch does. There was some > > discussion about making determine_rate mandatory for muxes[1] and this > > patch should help with this in addition to making it easier to sync > > more video resolutions on the 8m Mini and Nano. > > Those patches have been queued by Stephen for 6.6 :)
One of the patches in the older series was reverted, but this was to address the patch that was reverted.
adam > > Maxime
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