[PATCH v3] clk: qcom: clk-alpha-pll: fix rate setting for Stromer PLLs

[Gabor Juhos <j4g8y7@gmail.com>]

The clk_alpha_pll_stromer_set_rate() function writes inproper
values into the ALPHA_VAL{,_U} registers which results in wrong
clock rates when the alpha value is used.

The broken behaviour can be seen on IPQ5018 for example, when
dynamic scaling sets the CPU frequency to 800000 KHz. In this
case the CPU cores are running only at 792031 KHz:

  # cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
  800000
  # cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
  792031

This happens because the function ignores the fact that the alpha
value calculated by the alpha_pll_round_rate() function is only
32 bits wide which must be extended to 40 bits if it is used on
a hardware which supports 40 bits wide values.

Extend the clk_alpha_pll_stromer_set_rate() function to convert
the alpha value to 40 bits before wrinting that into the registers
in order to ensure that the hardware really uses the requested rate.

After the change the CPU frequency is correct:

  # cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
  800000
  # cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
  800000

Cc: stable@vger.kernel.org
Fixes: e47a4f55f240 ("clk: qcom: clk-alpha-pll: Add support for Stromer PLLs")
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Gabor Juhos <j4g8y7@gmail.com>
---
Changes in v3:
  - remove constants' comparison (Konrad)
  - Link to v2: https://lore.kernel.org/r/20240326-alpha-pll-fix-stromer-set-rate-v2-1-48ae83af71c8@gmail.com

Changes in v2:
  - fix subject prefix
  - rebase on v6.9-rc1
  - Link to v1: https://lore.kernel.org/r/20240324-alpha-pll-fix-stromer-set-rate-v1-1-335b0b157219@gmail.com

Depends on the following patch:
  https://lore.kernel.org/r/20240315-apss-ipq-pll-ipq5018-hang-v2-1-6fe30ada2009@gmail.com
---
 drivers/clk/qcom/clk-alpha-pll.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/clk/qcom/clk-alpha-pll.c b/drivers/clk/qcom/clk-alpha-pll.c
index 8a412ef47e16..8a8abb429577 100644
--- a/drivers/clk/qcom/clk-alpha-pll.c
+++ b/drivers/clk/qcom/clk-alpha-pll.c
@@ -2490,6 +2490,8 @@ static int clk_alpha_pll_stromer_set_rate(struct clk_hw *hw, unsigned long rate,
 	rate = alpha_pll_round_rate(rate, prate, &l, &a, ALPHA_REG_BITWIDTH);
 
 	regmap_write(pll->clkr.regmap, PLL_L_VAL(pll), l);
+
+	a <<= ALPHA_REG_BITWIDTH - ALPHA_BITWIDTH;
 	regmap_write(pll->clkr.regmap, PLL_ALPHA_VAL(pll), a);
 	regmap_write(pll->clkr.regmap, PLL_ALPHA_VAL_U(pll),
 		     a >> ALPHA_BITWIDTH);

---
base-commit: 4cece764965020c22cff7665b18a012006359095
change-id: 20240324-alpha-pll-fix-stromer-set-rate-472376e624f0

Best regards,
-- 
Gabor Juhos <j4g8y7@gmail.com>