linux-kernel - Re: [PATCH v7 6/9] interconnect: qcom: rpm: Handle interface clocks

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Message-ID: <CAA8EJpqh+A_YKbhSQB5sWj4EP9eQtNHeohDira9o-jrx3pPRNg@mail.gmail.com>
Date:   Sat, 11 Mar 2023 16:35:44 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     "Bryan O'Donoghue" <bryan.odonoghue@...aro.org>
Cc:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Georgi Djakov <djakov@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 6/9] interconnect: qcom: rpm: Handle interface clocks

On Sat, 11 Mar 2023 at 16:29, Bryan O'Donoghue
<bryan.odonoghue@...aro.org> wrote:
>
> On 11/03/2023 14:01, Dmitry Baryshkov wrote:
> >>
> >> Limit the number of bus_clocks to 2 (which is the maximum that SMD
> >> RPM interconnect supports anyway) and handle non-scaling clocks
> >> separately. Update MSM8996 and SDM660 drivers to make sure they do
> >> not regress with this change.
> >>
> >> This unfortunately has to be done in one patch to prevent either
> >> compile errors or broken bisect.
> >
> > Can we determine somehow if the intf clocks are required for the whole
> > NoC or just for a single node? I don't think that clocks like a0noc_ufs
> > are requiered to be up for the whole aggre_noc. Instead they probably
> > have to be enabled only when UFS makes use of the NoC (in other words
> > when is has voted for the bandwidth).
>
> Its probably worthwhile experimenting to see if the *ufs*_clk can/should
> be added to the UFS device list of clocks.

While we were doing this for some of the clocks (PCIe and USB, if I'm
not mistaken), I think that generally this is not fully correct. In my
opinion it should be in the interconnect driver, who turns
corresponding clocks on and off. These clocks correspond to the SoC
topology, rather than the end-device.

>
> I hadn't realised we were talking about enabling the intf clocks always
> but, actually that is what we are talking about isn't it ?
>
> It seems pretty unlikely that other devices would depend on clocks named
> *ufs*
>
> OTOH "clk-aggre2-noc-clk-no-rate" may be used across different nodes,
> seems like a pretty generic name, though still suspicious it is bundled
> with UFS, likely it is only required for UFS ?!?
>
> Konrad can you try:
>
> 1. Moving the intf_clks/QoS clocks be contained to UFS alone ?
> 2. If that doesn't work just the *ufs* clocks be put there with
> 2a. "clk-aggre2-noc-clk-no-rate" alone added to the intf_clk list
>
> It seems wrong to be enabling ufs related NoC clocks unless we are
> actually switching on UFS.

-- 
With best wishes
Dmitry