netdev - Re: [PATCH v4 2/8] clk: qcom: ipq5332: enable few nssnoc clocks in driver probe

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Date: Tue, 5 Mar 2024 08:41:19 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Kathiravan Thirumoorthy <quic_kathirav@...cinc.com>
Cc: Andrew Lunn <andrew@...n.ch>, Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konrad.dybcio@...aro.org>, Michael Turquette <mturquette@...libre.com>, 
	Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Richard Cochran <richardcochran@...il.com>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org, 
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 2/8] clk: qcom: ipq5332: enable few nssnoc clocks in
 driver probe

On Fri, 23 Feb 2024 at 12:18, Kathiravan Thirumoorthy
<quic_kathirav@...cinc.com> wrote:
>
>
>
> On 2/19/2024 3:53 PM, Dmitry Baryshkov wrote:
> > On Sun, 18 Feb 2024 at 06:29, Kathiravan Thirumoorthy
> > <quic_kathirav@...cinc.com> wrote:
> >>
> >>
> >>
> >> On 2/17/2024 10:15 PM, Dmitry Baryshkov wrote:
> >>> On Sat, 17 Feb 2024 at 17:45, Kathiravan Thirumoorthy
> >>> <quic_kathirav@...cinc.com> wrote:
> >>>>
> >>>>
> >>>> <snip>
> >>>>
> >>>>>> Reason being, to access the NSSCC clocks, these GCC clocks
> >>>>>> (gcc_snoc_nssnoc_clk, gcc_snoc_nssnoc_1_clk, gcc_nssnoc_nsscc_clk)
> >>>>>> should be turned ON. But CCF disables these clocks as well due to the
> >>>>>> lack of consumer.
> >>>>>
> >>>>> This means that NSSCC is also a consumer of those clocks. Please fix
> >>>>> both DT and nsscc driver to handle NSSNOC clocks.
> >>>>
> >>>>
> >>>> Thanks Dmitry. I shall include these clocks in the NSSCC DT node and
> >>>> enable the same in the NSSCC driver probe.
> >>>
> >>> Or use them through pm_clk. This might be better, as the system
> >>> doesn't need these clocks if NSSCC is suspended.
> >>
> >>
> >> IPQ53XX SoC doesn't support the PM(suspend / resume) functionality, so
> >> that, can I enable these clocks in NSSCC driver probe itself?
> >
> > There is a difference between PM (suspend/resume) and runtime PM.
> >
> >
>
> Thanks Dmitry. IIUC your question correctly, runtime PM for the
> peripherals are not supported (except CPU cores which supports DVFS).
> Since these are router based products, once system is powered on, all
> the peripherals are configured to the required frequency and it will be
> never go into low power modes.
>
> Please let me know if this answers your questions.

It seems there is a misunderstanding somewhere. Runtime PM allows the
Linux kernel to disable temporary unused devices at runtime. E.g. if
the NSS is switched off, the kernel can switch NSSCC off too, cutting
the power. It has nothing to do with the frequency of the device /
clock or with the product being a router or a mobile device.


-- 
With best wishes
Dmitry