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Message-ID: <8568eead-90f6-ce15-d483-4d72dbab6294@linaro.org>
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
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