linux-kernel - Re: [PATCH 2/2] PCI: qcom: Add basic interconnect support

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Message-ID: <Y1F8MqeHxj5IaLtx@x1>
Date:   Thu, 20 Oct 2022 12:49:54 -0400
From:   Brian Masney <bmasney@...hat.com>
To:     Johan Hovold <johan+linaro@...nel.org>
Cc:     Stanimir Varbanov <svarbanov@...sol.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Krishna chaitanya chundru <quic_krichai@...cinc.com>,
        quic_vbadigan@...cinc.com, linux-arm-msm@...r.kernel.org,
        linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] PCI: qcom: Add basic interconnect support

On Mon, Oct 17, 2022 at 01:24:49PM +0200, Johan Hovold wrote:
> On Qualcomm platforms like SC8280XP and SA8540P interconnect bandwidth
> must be requested before enabling interconnect clocks.
> 
> Add basic support for managing an optional "pcie-mem" interconnect path
> by setting a low constraint before enabling clocks and updating it after
> the link is up.
> 
> Note that it is not possible for a controller driver to set anything but
> a maximum peak bandwidth as expected average bandwidth will vary with
> use case and actual use (and power policy?). This very much remains an
> unresolved problem with the interconnect framework.
> 
> Also note that no constraint is set for the SC8280XP/SA8540P "cpu-pcie"
> path for now as it is not clear what an appropriate constraint would be
> (and the system does not crash when left unspecified currently).
> 
> Fixes: 70574511f3fc ("PCI: qcom: Add support for SC8280XP")
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>

Reviewed-by: Brian Masney <bmasney@...hat.com>