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Subject: Re: [PATCH v4 1/3] arm64: dts: qcom: sc7280: Add proxy interconnect
 requirements for modem
To:     Stephen Boyd <swboyd@chromium.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>
CC:     <robh+dt@kernel.org>, <krzysztof.kozlowski+dt@linaro.org>,
        <ohad@wizery.com>, <agross@kernel.org>,
        <mathieu.poirier@linaro.org>, <linux-arm-msm@vger.kernel.org>,
        <linux-remoteproc@vger.kernel.org>, <devicetree@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <mka@chromium.org>
References: <1652978825-5304-1-git-send-email-quic_sibis@quicinc.com>
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 <CAE-0n53hDDoetQW0Bz7noq4peuNCyrGsXaJdjFj=4sMkGeZFgw@mail.gmail.com>
From:   Sibi Sankar <quic_sibis@quicinc.com>
Message-ID: <3e7e8263-fdc1-ffa8-7b7f-188bb027fadf@quicinc.com>
Date:   Thu, 26 May 2022 16:46:51 +0530
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On 5/21/22 12:37 AM, Stephen Boyd wrote:
> Quoting Sibi Sankar (2022-05-20 11:08:52)
>> Hey Bjorn,
>> Thanks for taking time to review the series.
>>
>> On 5/20/22 2:05 AM, Bjorn Andersson wrote:
>>> On Thu 19 May 09:47 PDT 2022, Sibi Sankar wrote:
>>>
>>>> Add interconnects that are required to be proxy voted upon during modem
>>>> bootup on SC7280 SoCs.
>>>
>>> This looks reasonable, but how come the vote is only for DDR frequency?
>>> What about the buses between modem and ddr?
>>
>> The proxy votes that are put in aren't for perf related reasons, the
>> modem was getting llcc timeouts while trying to read contents from
>> memory. The hw team recommended the proxy votes as the fix.
> 
> Presumably the bootloader sets up some initial modem and ddr bus
> bandwidth requests? Or the modem bootloader stage (MSA?) handles that
> part?

Stephen/Bjorn,
Sorry for the delay, took a while to dig this up. The modem interconnect
is connected directly to gemnoc ddr. The path info from modem --> ddr is
split up into modem --> llcc and llcc --> ddr (Similar to CPUs) i.e. in
the end scaling of the path involves scaling of the two clocks, gemnoc
and ddr. There isn't any default vote for modem --> llcc as such but it
gets implicitly scaled when we vote max for llcc --> ddr path due to
dependency maintained between the two clocks by rpmh.

-Sibi

>