clk: imx: composite-8m: Add imx8m_divider_determine_rate

Browse source

[ Upstream commit 8208181fe5 ]

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: 690dccc4a0 ("Revert "clk: imx: composite-8m: Add support to determine_rate"")
Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Abel Vesa <abel.vesa@linaro.org>
Tested-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20230506195325.876871-1-aford173@gmail.com
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

...

This commit is contained in:

Adam Ford 2023-05-06 14:53:25 -05:00 • committed by Greg Kroah-Hartman

parent 1635eb05c3

commit ae86e657d5

1 changed files with 31 additions and 0 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

31

drivers/clk/imx/clk-composite-8m.c

View file