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

[Chuan Liu]

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On 2024/9/4 15:18, chuan.liu at amlogic.com wrote:
> From: Chuan Liu <chuan.liu at amlogic.com>
>
> 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 at linaro.org>
> To: Jerome Brunet <jbrunet at baylibre.com>
> To: Michael Turquette <mturquette at baylibre.com>
> To: Stephen Boyd <sboyd at kernel.org>
> To: Kevin Hilman <khilman at baylibre.com>
> To: Martin Blumenstingl <martin.blumenstingl at googlemail.com>
> Cc:  <linux-amlogic at lists.infradead.org>
> Cc:  <linux-clk at vger.kernel.org>
> Cc:  <linux-arm-kernel at lists.infradead.org>
> Cc:  <linux-kernel at vger.kernel.org>
> Signed-off-by: Chuan Liu <chuan.liu at amlogic.com>
>
>
> --- b4-submit-tracking ---
> # This section is used internally by b4 prep for tracking purposes.
> {
>    "series": {
>      "revision": 1,
>      "change-id": "20240904-fix_clk-668f7a1a2b16",
>      "prefixes": []
>    }
> }