linux-kernel - Re: [PATCH v3 4/6] clk: qcom: clk-rcg2: don't re-search config on rcg2_set

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Date:   Thu, 30 Mar 2023 01:01:55 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Stephen Boyd <sboyd@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Christian Marangi <ansuelsmth@...il.com>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/6] clk: qcom: clk-rcg2: don't re-search config on
 rcg2_set_rate

On 29/03/2023 22:52, Stephen Boyd wrote:
> Quoting Christian Marangi (2023-01-17 05:54:57)
>> Currently the rcg2 driver search the rate to apply 2 times.
>> - In _freq_tbl_determine_rate for the determine_rate function used by
>>    core clk to understand the best rate to set with set_rate
>> - In rcg2_set_rate where the suggested rate is not trusted and searched
>>    another time using a CEIL or FLOOR policy.
>>
>> This is fundamentally wrong as we are ignoring what core clock is
>> deciding and just setting whatever clock configuration we want for the
>> suggested clock. The problem is in the fact that the correct clock
>> should have already be searched and selected with the determine_rate
>> function and set_rate should just apply whatever clock was provided.
> 
> It sounds like you're assuming the rate coming into the set_rate clk_op
> is rounded? Don't make that assumption. The set_rate clk_op should round
> the rate again. The parent rate could have changed.

My fault, I suggested this some time ago on the basis that... "CCF 
switching the parent rate during the clk_set_rate() call. Then the 
second lookup might end up selecting different parent/mnd configuration."

-- 
With best wishes
Dmitry