linux-kernel - Re: [PATCH v10 5/6] soc: qcom: Add support for Core Power Reduction v3, v4 and Hardened

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Date:   Tue, 28 Feb 2023 09:19:24 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>,
        Niklas Cassel <nks@...wful.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Robert Marko <robimarko@...il.com>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-pm@...r.kernel.org,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>
Subject: Re: [PATCH v10 5/6] soc: qcom: Add support for Core Power Reduction
 v3, v4 and Hardened

Il 27/02/23 14:20, Dmitry Baryshkov ha scritto:
> On Mon, 27 Feb 2023 at 15:06, AngeloGioacchino Del Regno
> <angelogioacchino.delregno@...labora.com> wrote:
>>
>> Il 27/02/23 13:01, Dmitry Baryshkov ha scritto:
>>>
>>> I took a glance at the 'cpufreq: qcom-hw: Implement CPRh aware OSM programming'
>>> patch, it doesn't seem to use the header (maybe I checked the older version of the
>>> patch). As for me, this is another signal that cpr_ext_data should come together
>>> with the LUT programming rather than with the CPRh itself.
>>>
>>>> Konrad, perhaps you can send the cpufreq-hw commits in a separate series, in
>>>> which cover letter you mention a dependency on this one?
>>>> That would *clearly* show the full picture to reviewers.
>>>
>>> Yes, that would be great. A small note regarding those patches. I see that you
>>> patched the qcom-cpufreq-hw.c. This way first the driver programs the LUT, then it
>>> reads it back to setup the OPPs. Would it be easier to split OSM-not-programmed
>>> driver?
>>>
>>
>> When I engineered that solution, I kept the cpufreq-hw reading *again* the values
>> from OSM to keep the driver *fully* compatible with the bootloader-programmed OSM
>> flow, which makes one thing (in my opinion) perfectly clear: that programming
>> sequence is exactly the same as what happens "under the hood" on SDM845 (and later)
>> but performed here-instead-of-there (linux instead of bootloader), with the actual
>> scaling driver being 100% the same between the two flows in the end.
>>
>> Having two drivers as you suggested would indeed achieve the same, but wouldn't be
>> any easier... if you do that, you'd have to *somehow* make sure that the
>> programming driver does its job before the cpufreq driver tries to read the OSM
>> status, adding one more link to an already long chain.
>>
>> Besides, I remember that this question got asked a while ago on the mailing lists
>> and there was a short discussion about it:
>>
>> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2555580.html
> 
> Ack, I see. Maybe splitting LUT programming to a separate source file
> would emphasise the fact that it is only required for some (older)

Maybe. I'm not sure it's worth adding a new helper file, but I don't really have
any strong arguments against...

Konrad, your call.

Cheers!
Angelo

> SoCs. Other than that, I have no additional comments for that series.
>