linux-kernel - Re: [PATCH 00/53] icc-rpmh multi-RSC voting groundwork

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Date:   Fri, 15 Sep 2023 09:05:25 -0700
From:   Mike Tipton <quic_mdtipton@...cinc.com>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
CC:     Georgi Djakov <djakov@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        <cros-qcom-dts-watchers@...omium.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 00/53] icc-rpmh multi-RSC voting groundwork

On Fri, Sep 15, 2023 at 03:43:27PM +0200, Konrad Dybcio wrote:
> On 14.09.2023 04:32, Mike Tipton wrote:
> > On Wed, Sep 13, 2023 at 10:31:49AM +0200, Konrad Dybcio wrote:
> >>> The applicable voters should likely be defined in the target-specific
> >>> headers, rather than the common qcom,icc.h. The bit range used for them
> >>> could be common, but each target may only support a small subset of the
> >>> total set of possible voters across all targets.
> >> I'm not sure how client drivers would then choose the
> >> correct path other than
> >>
> >> switch (soc) {
> >> case 8450:
> >> 	tag = QCOM_ICC_TAG_VOTER_8450_HLOS;
> >> 	break;
> >> case 8550:
> >> 	tag = QCOM_ICC_TAG_VOTER_8550_HLOS;
> >> 	break;
> >> ...
> >> }
> >>
> >> which would be unacceptable.
> > 
> > The same general way it's handled for the endpoint bindings, which are
> > already target-specific. 
> > 
> > Any client drivers hardcoding the endpoint bindings in their driver
> > would have to include the appropriate, target-specific binding header
> > (e.g. qcom,sm8550-rpmh.h). That would only be possible if their driver
> > file is itself target-specific. Otherwise, it would have to pull the
> > endpoint bindings from devicetree. Or just use the recommended
> > of_icc_get() and let devicetree do everything for them. Same for the
> > target-specific voter tag bindings.
> > 
> > Clients can also specify their tags in devicetree. They don't actually
> > have to call icc_set_tag() directly. For example:
> > 
> >     #include <dt-bindings/interconnect/qcom,sm8450.h>
> > 
> >     interconnects = <&mmss_noc MASTER_MDP QCOM_ICC_TAG_VOTER_DISP
> >                      &mc_virt SLAVE_EBI1 QCOM_ICC_TAG_VOTER_DISP>;
> > 
> > Then when they call of_icc_get() for this path it'll automatically have
> > QCOM_ICC_TAG_VOTER_DISP set for them.
> I think I'd skew towards the "define everything in the DT" approach.
> 
> One thing that makes me uneasy to go on with this approach is the
> question whether there is a case in which we would want to switch
> from e.g. voting through DISP to voting through APPS (or similar)
> from within a single device.

It shouldn't be common. But it could be done fairly simply by listing
paths for each different voter in the dt properties. 

    interconnects = <&mmss_noc MASTER_MDP QCOM_ICC_TAG_VOTER_APPS
                     &mc_virt SLAVE_EBI1  QCOM_ICC_TAG_VOTER_APPS>,
                    <&mmss_noc MASTER_MDP QCOM_ICC_TAG_VOTER_DISP
                     &mc_virt SLAVE_EBI1  QCOM_ICC_TAG_VOTER_DISP>,
    interconnect-names = "path-apps-voter",
                         "path-disp-voter";