[PATCH 1/5] clk: meson: Fix an issue with inaccurate hifi_pll frequency

[chuan.liu]

From: Chuan Liu <chuan.liu@xxxxxxxxxxx>

Some PLLs with fractional multipliers have fractional denominators that
are fixed to "100000" instead of the previous "(1 << pll->frac.width)".

The hifi_pll for both C3 and S4 supports a fractional multiplier and has
a fixed fractional denominator of "100000".

Here are the results of the C3-based command tests (already defined
CLOCK_ALLOW_WRITE_DEBUGFS):
# echo 491520000 > /sys/kernel/debug/clk/hifi_pll/clk_rate
# cat /sys/kernel/debug/clk/hifi_pll/clk_rate
491520000
# echo 1 > /sys/kernel/debug/clk/hifi_pll/clk_prepare_enable
# cat /sys/kernel/debug/meson-clk-msr/clks/hifi_pll_clk
491515625       +/-15625Hz
# devmem 0xfe008100 32
0xD00304A3
# devmem 0xfe008104 32
0x00014820

Based on the register information read above, it can be obtained:
m = 0xA3 = 0d163;
n = 0x1 = 0d1
frac = 0x14820 = 0d84000
od = 0x3 = 0d3

hifi_pll calculates the output frequency:
calc_rate = xtal_rate / n * (m + (frac / frac_max)) >> od;
calc_rate = 24000000 / 1 * (163 + (84000 / 100000)) >> 3;
calc_rate = 491520000

clk_rate, msr_rate, and calc_rate all match.

The test and calculation results of S4 are consistent with those of C3,
which will not be repeated here.

To: Neil Armstrong <neil.armstrong@xxxxxxxxxx>
To: Jerome Brunet <jbrunet@xxxxxxxxxxxx>
To: Michael Turquette <mturquette@xxxxxxxxxxxx>
To: Stephen Boyd <sboyd@xxxxxxxxxx>
To: Kevin Hilman <khilman@xxxxxxxxxxxx>
To: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx>
Cc:  <linux-amlogic@xxxxxxxxxxxxxxxxxxx>
Cc:  <linux-clk@xxxxxxxxxxxxxxx>
Cc:  <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>
Cc:  <linux-kernel@xxxxxxxxxxxxxxx>
Signed-off-by: Chuan Liu <chuan.liu@xxxxxxxxxxx>


--- b4-submit-tracking ---
# This section is used internally by b4 prep for tracking purposes.
{
  "series": {
    "revision": 1,
    "change-id": "20240904-fix_clk-668f7a1a2b16",
    "prefixes": []
  }
}
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2.42.0