Message-ID: <CAA8EJpqENsojPQmCbma_nQLEZq8nK1fz1K0JdtvLd=kPrH_DBw@mail.gmail.com>
Date: Wed, 8 May 2024 11:10:18 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Varadarajan Narayanan <quic_varada@...cinc.com>
Cc: Georgi Djakov <djakov@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.org>, andersson@...nel.org, 
	mturquette@...libre.com, sboyd@...nel.org, robh@...nel.org, 
	krzk+dt@...nel.org, conor+dt@...nel.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 Wed, 8 May 2024 at 09:53, Varadarajan Narayanan
<quic_varada@...cinc.com> wrote:
>
> On Fri, May 03, 2024 at 04:51:04PM +0300, Georgi Djakov wrote:
> > Hi Varada,
> >
> > Thank you for your work on this!
> >
> > On 2.05.24 12:30, Varadarajan Narayanan wrote:
> > > On Tue, Apr 30, 2024 at 12:05:29PM +0200, Konrad Dybcio wrote:
> > > > On 25.04.2024 12:26 PM, Varadarajan Narayanan wrote:
> > > > > 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.
> > > >
> > > > No, with sync_state it actually does "something" (sets the interconnect
> > > > path bandwidths to zero). And *this* patch does nothing functionally,
> > > > it only makes the dt checker happy.
> > >
> > > I understand.
> > >
> > > > > 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";
> > > >
> > > > Okay. What about USB that's already enabled? And BIMC/MEMNOC?
> > >
> > > For USB, the GCC_ANOC_USB_AXI_CLK is enabled as part of the iface
> > > clock. Hence, interconnect is not specified there.
> > >
> > > MEMNOC to System NOC interfaces seem to be enabled automatically.
> > > Software doesn't have to turn on or program specific clocks.
> > >
> > > > > > 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.
> > > >
> > > > Have you confirmed that the registers are actually written to, and with
> > > > correct values?
> > >
> > > I tried the following combinations:-
> > >
> > > 1. Top of tree linux-next + This patch set
> > >
> > >     * icc_sync_state called
> > >     * No crash or hang observed
> > >     * From /sys/kernel/debug/clk/clk_summary can see the
> > >       relevant clocks are set to the expected rates (compared
> > >       with downstream kernel)
> > >
> > > 2. Top of tree linux-next + This patch set + PCIe enablement
> > >
> > >     * icc_sync_state NOT called
> >
> > If sync_state() is not being called, that usually means that there
> > are interconnect consumers that haven't probed successfully (PCIe?)
> > or their dependencies. That can be checked in /sys/class/devlink/.../status
> > But i am not sure how this works for PCI devices however.
> >
> > You can also manually force a call to sync_state by writing "1" to
> > the interconnect provider's /sys/devices/.../state_synced
> >
> > Anyway, the question is if PCIe and NSS work without this driver?
>
> No.
>
> > If they work, is this because the clocks are turned on by default
> > or by the boot loader?
>
> Initially, the PCIe/NSS driver enabled these clocks directly
> by having them in their DT nodes itself. Based on community
> feedback this was removed and after that PCIe/NSS did not work.
>
> > Then if an interconnect path (clock) gets disabled either when we
> > reach a sync_state (with no bandwidth requests) or we explicitly
> > call icc_set_bw() with 0 bandwidth values, i would expect that
> > these PCIe and NSS devices would not function anymore (it might
> > save some power etc) and if this is unexpected we should see a
> > a crash or hang...
> >
> > Can you confirm this?
>
> With ICC enabled, icc_set_bw (with non-zero values) is called by
> PCIe and NSS drivers. Haven't checked with icc_set_bw with zero
> values.
>
> PCIe:   qcom_pcie_probe -> qcom_pcie_icc_init -> icc_set_bw
> NSS:    ppe_icc_init -> icc_set_bw
>
> I believe sync_state is not getting called since there is a
> non-zero set bandwidth request. Which seems to be aligned with
> your explanation.

This doesn't look correct. sync_state is being called once all
consumers are probed. It doesn't matter whether those consumers have
non-zero bandwidth requests or no.


-- 
With best wishes
Dmitry

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