linux-kernel - [PATCH v2] clk: qcom: clk-alpha-pll: fix rate setting for Stromer PLLs

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Date: Tue, 26 Mar 2024 13:15:51 +0100
From: Gabor Juhos <j4g8y7@...il.com>
To: Bjorn Andersson <andersson@...nel.org>, 
 Konrad Dybcio <konrad.dybcio@...aro.org>, 
 Michael Turquette <mturquette@...libre.com>, 
 Stephen Boyd <sboyd@...nel.org>, 
 Varadarajan Narayanan <quic_varada@...cinc.com>, 
 Sricharan R <quic_srichara@...cinc.com>, 
 Kathiravan T <quic_kathirav@...cinc.com>
Cc: linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org, 
 linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
 Gabor Juhos <j4g8y7@...il.com>
Subject: [PATCH v2] clk: qcom: clk-alpha-pll: fix rate setting for Stromer
 PLLs

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@...r.kernel.org
Fixes: e47a4f55f240 ("clk: qcom: clk-alpha-pll: Add support for Stromer PLLs")
Signed-off-by: Gabor Juhos <j4g8y7@...il.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 | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/clk/qcom/clk-alpha-pll.c b/drivers/clk/qcom/clk-alpha-pll.c
index 8a412ef47e163..8e98198d4b4b6 100644
--- a/drivers/clk/qcom/clk-alpha-pll.c
+++ b/drivers/clk/qcom/clk-alpha-pll.c
@@ -2490,6 +2490,10 @@ 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);
+
+	if (ALPHA_REG_BITWIDTH > ALPHA_BITWIDTH)
+		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: 5eab983c5e31e5f0bf2d583731e320e21814d1b7
change-id: 20240324-alpha-pll-fix-stromer-set-rate-472376e624f0

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