linux-kernel - Re: [PATCH 2/2] interconnect: qcom: qcm2290: Enable sync state

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Date:   Fri, 21 Jul 2023 14:03:16 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Stephan Gerhold <stephan@...hold.net>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Georgi Djakov <djakov@...nel.org>,
        Shawn Guo <shawn.guo@...aro.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] interconnect: qcom: qcm2290: Enable sync state

On 20.07.2023 21:52, Stephan Gerhold wrote:
> On Thu, Jul 20, 2023 at 08:24:01PM +0200, Konrad Dybcio wrote:
>> Very surprisingly, qcm2290 does not seem to require any interface
>> clocks.
> 
> What does this mean exactly? The interconnect .sync_state() is
> responsible to drop the initial maximum bandwidth votes, with the
> assumption that all active devices have voted for the bandwidth they
> need. How does this relate to "requiring interface clocks"?
If it required such clocks to be present, sync_state could not
complete, as trying to access some nodes would crash the platform
due to unclocked access.

> 
>> It's therefore safe to enable sync_state to park unused devices.
>> Do so.
> 
> Doesn't this make everything painfully slow? There are no interconnect
> consumers at all in qcm2290.dtsi. I would expect that all bandwidths
> end up at minimum.
There are no interconnect providers defined in qcm2290.dtsi.

Konrad