linux-kernel - Re: [PATCH v9 6/6] arm64: dts: qcom: ipq9574: Add icc provider ability to gcc

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Message-ID: <Ziov6bWBXYXJ4Zp8@hu-varada-blr.qualcomm.com>
Date: Thu, 25 Apr 2024 15:56:49 +0530
From: Varadarajan Narayanan <quic_varada@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@...aro.org>
CC: <andersson@...nel.org>, <mturquette@...libre.com>, <sboyd@...nel.org>,
        <robh@...nel.org>, <krzk+dt@...nel.org>, <conor+dt@...nel.org>,
        <djakov@...nel.org>, <dmitry.baryshkov@...aro.org>,
        <quic_anusha@...cinc.com>, <linux-arm-msm@...r.kernel.org>,
        <linux-clk@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v9 6/6] arm64: dts: qcom: ipq9574: Add icc provider
 ability to gcc

On Tue, Apr 23, 2024 at 02:58:41PM +0200, Konrad Dybcio wrote:
>
>
> On 4/18/24 11:23, Varadarajan Narayanan wrote:
> > IPQ SoCs dont involve RPM in managing NoC related clocks and
> > there is no NoC scaling. Linux itself handles these clocks.
> > However, these should not be exposed as just clocks and align
> > with other Qualcomm SoCs that handle these clocks from a
> > interconnect provider.
> >
> > Hence include icc provider capability to the gcc node so that
> > peripherals can use the interconnect facility to enable these
> > clocks.
> >
> > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > Signed-off-by: Varadarajan Narayanan <quic_varada@...cinc.com>
> > ---
>
> If this is all you do to enable interconnect (which is not the case,
> as this patch only satisfies the bindings checker, the meaningful
> change happens in the previous patch) and nothing explodes, this is
> an apparent sign of your driver doing nothing.

It appears to do nothing because, we are just enabling the clock
provider to also act as interconnect provider. Only when the
consumers are enabled with interconnect usage, this will create
paths and turn on the relevant NOC clocks.

This interconnect will be used by the PCIe and NSS blocks. When
those patches were posted earlier, they were put on hold until
interconnect driver is available.

Once this patch gets in, PCIe for example will make use of icc.
Please refer to https://lore.kernel.org/linux-arm-msm/20230519090219.15925-5-quic_devipriy@quicinc.com/.

The 'pcieX' nodes will include the following entries.

	interconnects = <&gcc MASTER_ANOC_PCIE0 &gcc SLAVE_ANOC_PCIE0>,
			<&gcc MASTER_SNOC_PCIE0 &gcc SLAVE_SNOC_PCIE0>;
	interconnect-names = "pcie-mem", "cpu-pcie";

> The expected reaction to "enabling interconnect" without defining the
> required paths for your hardware would be a crash-on-sync_state, as all
> unused (from Linux's POV) resources ought to be shut down.
>
> Because you lack sync_state, the interconnects silently retain the state
> that they were left in (which is not deterministic), and that's precisely
> what we want to avoid.

I tried to set 'sync_state' to icc_sync_state to be invoked and
didn't see any crash.

Thanks
Varada