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

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Message-ID: <278f3baa-a760-18cf-1a43-2814793af987@linaro.org>
Date:   Thu, 15 Jun 2023 19:37:21 +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 19:35, Stephen Boyd wrote:
> Quoting Konrad Dybcio (2023-06-15 00:52:07)
>> 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.
>>
> 
> That's the intent. Probe the interconnect driver to get bus clk rate
> setting.
> 
> What are the !bus clocks managed by RPM?
Depending on the platform, that includes IPA, GPU, OCMEM, RF.. everything
that's not been separated out in patch 18.

Konrad