linux-kernel - Re: [PATCH v9 01/10] clk: qcom: clk-alpha-pll: Add support for dynamic update for slewing PLLs

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Message-ID: <c37349c0-8ec0-4654-bc82-15190509ddeb@oss.qualcomm.com>
Date: Fri, 27 Jun 2025 17:09:38 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Taniya Das <quic_tdas@...cinc.com>,
        Bjorn Andersson
 <andersson@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>
Cc: Ajit Pandey <quic_ajipan@...cinc.com>,
        Imran Shaik <quic_imrashai@...cinc.com>,
        Jagadeesh Kona <quic_jkona@...cinc.com>, linux-arm-msm@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v9 01/10] clk: qcom: clk-alpha-pll: Add support for
 dynamic update for slewing PLLs

On 6/25/25 12:31 PM, Taniya Das wrote:
> 
> 
> On 6/15/2025 12:20 AM, Konrad Dybcio wrote:
>> On 6/12/25 11:55 AM, Taniya Das wrote:
>>> The alpha PLLs which slew to a new frequency at runtime would require
>>> the PLL to calibrate at the mid point of the VCO. Add the new PLL ops
>>> which can support the slewing of the PLL to a new frequency.
>>>
>>> Reviewed-by: Imran Shaik <quic_imrashai@...cinc.com>
>>> Signed-off-by: Taniya Das <quic_tdas@...cinc.com>
>>> ---

[...]

>>> +	regmap_write(pll->clkr.regmap, PLL_L_VAL(pll), l);
>>> +	regmap_write(pll->clkr.regmap, PLL_ALPHA_VAL(pll), lower_32_bits(a));
>>> +	regmap_write(pll->clkr.regmap, PLL_ALPHA_VAL_U(pll), upper_32_bits(a));
>>> +
>>> +	/* Ensure that the write above goes before slewing the PLL */
>>> +	mb();
>>
>> Here however, the write may not arrive at the clock controller before you
>> proceed to slew_update()
>>
> 
> Yes, it is required here and will keep it.

You should change it to a readback instead

Konrad