linux-kernel - Re: [PATCH v6 00/22] Restructure RPM SMD ICC

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Date:   Thu, 15 Jun 2023 09:52:07 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Stephen Boyd <sboyd@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Evan Green <evgreen@...omium.org>,
        Georgi Djakov <djakov@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Stephan Gerhold <stephan@...hold.net>
Subject: Re: [PATCH v6 00/22] Restructure RPM SMD ICC

On 15.06.2023 02:49, Stephen Boyd wrote:
> Quoting Konrad Dybcio (2023-06-14 11:04:19)
>> This series reshuffles things around, moving the management of SMD RPM
>> bus clocks to the interconnect framework where they belong. This helps
>> us solve a couple of issues:
>>
>> 1. We can work towards unused clk cleanup of RPMCC without worrying
>>    about it killing some NoC bus, resulting in the SoC dying.
>>    Deasserting actually unused RPM clocks (among other things) will
>>    let us achieve "true SoC-wide power collapse states", also known as
>>    VDD_LOW and VDD_MIN.
>>
>> 2. We no longer have to keep tons of quirky bus clock ifs in the icc
>>    driver. You either have a RPM clock and call "rpm set rate" or you
>>    have a single non-RPM clock (like AHB_CLK_SRC) or you don't have any.
>>
>> 3. There's less overhead - instead of going through layers and layers of
>>    the CCF, ratesetting comes down to calling max() and sending a single
>>    RPM message. ICC is very very dynamic so that's a big plus.
>>
>> The clocks still need to be vaguely described in the clk-smd-rpm driver,
>> as it gives them an initial kickoff, before actually telling RPM to
>> enable DVFS scaling.  After RPM receives that command, all clocks that
>> have not been assigned a rate are considered unused and are shut down
>> in hardware, leading to the same issue as described in point 1.
> 
> Why can't we move the enable of DVFS scaling call to the interconnect
> driver as well? We want the clk driver to not reference the interconnect
> resources at all.
That would result in no rpmcc ratesetting on platforms without a functional
interconnect driver. The DVFS call concerns both bus and !bus clocks.

Konrad