[PATCH v3 0/3] clk: meson: Fix an issue with inaccurate hifi_pll frequency

[Chuan Liu via B4 Relay]

Some PLLS with fractional multipliers have fractional denominators with
fixed values, instead of the previous "(1 << pll-> frc.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.

Signed-off-by: Chuan Liu <chuan.liu@xxxxxxxxxxx>
---
Changes in v3:
- Drop the call to unlikely().
- Link to v2: https://lore.kernel.org/r/20240906-fix_clk-v2-0-7a3941eb2cdf@xxxxxxxxxxx

Changes in v2:
- Added frac_max to the pll parameter instead of flag.
- frac_max is added to hifi_pll for C3 and S4.
- Link to v1: https://lore.kernel.org/r/20240906-fix_clk-v1-0-2977ef0d72e7@xxxxxxxxxxx

---
Chuan Liu (3):
      clk: meson: Support PLL with fixed fractional denominators
      clk: meson: c3: pll: fix frac maximum value for hifi_pll
      clk: meson: s4: pll: fix frac maximum value for hifi_pll

 drivers/clk/meson/c3-pll.c  | 1 +
 drivers/clk/meson/clk-pll.c | 8 +++++---
 drivers/clk/meson/clk-pll.h | 1 +
 drivers/clk/meson/s4-pll.c  | 1 +
 4 files changed, 8 insertions(+), 3 deletions(-)
---
base-commit: 80344f4c1a1edec507a20adca476af84ea58cd4c
change-id: 20240904-fix_clk-668f7a1a2b16

Best regards,
-- 
Chuan Liu <chuan.liu@xxxxxxxxxxx>