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

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Message-ID: <ZL0InL6slLRNcVkI@gerhold.net>
Date:   Sun, 23 Jul 2023 13:01:48 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
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 Fri, Jul 21, 2023 at 02:03:16PM +0200, Konrad Dybcio wrote:
> 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.

You mean something like the IPA clock that must be active to do the QoS
writes?

Wouldn't it already crash before .sync_state() then, when the initial
max bandwidth votes are being made?

> 
> > 
> >> 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.

Ack, so I guess you're going to add them together with the actual
consumers?

I think the patch itself is fine. Only the commit message is a bit
misleading. The actual change that is being done here is enabling the
bandwidth scaling (dropping the max bandwidth votes after
.sync_state()). Can you try to clarify the commit message a bit?

Thanks,
Stephan