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

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Date:   Wed, 13 Sep 2023 19:32:39 -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 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.