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

Varadarajan Narayanan
2024-05-08T06:53:10Z

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@linaro.org>
> > > > > > Signed-off-by: Varadarajan Narayanan <quic_varada@quicinc.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.

Thanks
Varada

>
> Thanks,
> Georgi
>
> > * 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)
> >
> > Does this answer your question? Please let me know if you were
> > looking for some other information.
> >
> > Thanks
> > Varada
> >
>