linux-kernel - Re: [PATCH v2 1/5] clk: qcom: cmnpll: Account for reference clock divider

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Message-ID: <d03335ba-2870-483b-aa35-89be284c219e@oss.qualcomm.com>
Date: Thu, 8 Jan 2026 11:23:38 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Jie Luo <jie.luo@....qualcomm.com>,
        Bjorn Andersson
 <andersson@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, Luo Jie <quic_luoj@...cinc.com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        quic_kkumarcs@...cinc.com, quic_linchen@...cinc.com,
        quic_leiwei@...cinc.com, quic_pavir@...cinc.com,
        quic_suruchia@...cinc.com
Subject: Re: [PATCH v2 1/5] clk: qcom: cmnpll: Account for reference clock
 divider

On 1/8/26 7:39 AM, Jie Luo wrote:
> 
> 
> On 1/7/2026 8:16 PM, Konrad Dybcio wrote:
>> On 1/7/26 6:35 AM, Luo Jie wrote:
>>> The clk_cmn_pll_recalc_rate() function must account for the reference clock
>>> divider programmed in CMN_PLL_REFCLK_CONFIG. Without this fix, platforms
>>> with a reference divider other than 1 calculate incorrect CMN PLL rates.
>>> For example, on IPQ5332 where the reference divider is 2, the computed rate
>>> becomes twice the actual output.
>>>
>>> Read CMN_PLL_REFCLK_DIV and divide the parent rate by this value before
>>> applying the 2 * FACTOR scaling. This yields the correct rate calculation:
>>> rate = (parent_rate / ref_div) * 2 * factor.
>>>
>>> Maintain backward compatibility with earlier platforms (e.g. IPQ9574,
>>> IPQ5424, IPQ5018) that use ref_div = 1.
>>>
>>> Fixes: f81715a4c87c ("clk: qcom: Add CMN PLL clock controller driver for IPQ SoC")
>>> Signed-off-by: Luo Jie <jie.luo@....qualcomm.com>
>>> ---
>>>  drivers/clk/qcom/ipq-cmn-pll.c | 11 +++++++++--
>>>  1 file changed, 9 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/clk/qcom/ipq-cmn-pll.c b/drivers/clk/qcom/ipq-cmn-pll.c
>>> index dafbf5732048..369798d1ce42 100644
>>> --- a/drivers/clk/qcom/ipq-cmn-pll.c
>>> +++ b/drivers/clk/qcom/ipq-cmn-pll.c
>>> @@ -185,7 +185,7 @@ static unsigned long clk_cmn_pll_recalc_rate(struct clk_hw *hw,
>>>  					     unsigned long parent_rate)
>>>  {
>>>  	struct clk_cmn_pll *cmn_pll = to_clk_cmn_pll(hw);
>>> -	u32 val, factor;
>>> +	u32 val, factor, ref_div;
>>>  
>>>  	/*
>>>  	 * The value of CMN_PLL_DIVIDER_CTRL_FACTOR is automatically adjusted
>>> @@ -193,8 +193,15 @@ static unsigned long clk_cmn_pll_recalc_rate(struct clk_hw *hw,
>>>  	 */
>>>  	regmap_read(cmn_pll->regmap, CMN_PLL_DIVIDER_CTRL, &val);
>>>  	factor = FIELD_GET(CMN_PLL_DIVIDER_CTRL_FACTOR, val);
>>> +	if (WARN_ON(factor == 0))
>>> +		factor = 1;
>>
>> FWIW the docs tell me the value of this field is '192' on IPQ5332..
>>
>> Konrad
> 
> Although the register description lists the default value as 192, the
> actual runtime value is 125 on IPQ5332, as shown in the dump below.
> 
> # devmem 0x9B794
> 0x00006C7D
> 
> # cat /sys/kernel/debug/clk/clk_summary | grep cmn_pll -B 2
>  xo-clk                              1       1        0        48000000
>   0          0     50000      Y   deviceless
> no_connection_id
>     ref-48mhz-clk                    2       2        0        48000000
>   0          0     50000      Y      deviceless
> no_connection_id
>        cmn_pll                       3       3        0
> 6000000000  0          0     50000      Y         deviceless
>          no_connection_id

Aaah I totally forgot about the xo rate in the calculations.. 1 vs 2
vs 100-something threw me off :)

Reviewed-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>

Konrad