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

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Date: Tue, 26 Mar 2024 14:26:16 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Gabor Juhos <j4g8y7@...il.com>
Cc: 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>, linux-arm-msm@...r.kernel.org, 
	linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org
Subject: Re: [PATCH v2] clk: qcom: clk-alpha-pll: fix rate setting for Stromer PLLs

On Tue, 26 Mar 2024 at 14:16, Gabor Juhos <j4g8y7@...il.com> wrote:
>
> 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(+)

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

-- 
With best wishes
Dmitry