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

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Date: Wed, 27 Mar 2024 18:19:36 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Gabor Juhos <j4g8y7@...il.com>, Bjorn Andersson <andersson@...nel.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
Subject: Re: [PATCH v2] clk: qcom: clk-alpha-pll: fix rate setting for Stromer
 PLLs

On 26.03.2024 11:16 PM, Gabor Juhos wrote:
> 2024. 03. 26. 21:51 keltezéssel, Konrad Dybcio írta:
> 
> ...
>>> 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;
>>
>> Uh.. that's not right, this is comparing two constants
>>
>> Did you mean to use pll_alpha_width()?
> 
> No, not in this patch at least.
> 
> The clk_alpha_pll_stromer_set_rate() function assumes that the alpha register is
> 40 bits wide, and currently it does not use pll_alpha_width() at all.
> Originally, I have converted the function to use it, but that made the change
> unnecessarily complex since it was a mix of a fix and of a rework.
> 
> The current patch is a simplified version of that, but i forgot to drop the
> comparison at the end of the process.
> 
> In order to keep this fix as simple as possible and backportable to stable
> kernels, I would rather remove the comparison to reduce the change to a
> single-line addition. Then modifying the code to use pll_alpha_width() can be
> done in a separate change.

Sounds good

Konrad