linux-kernel - Re: [PATCH V4 12/16] Documentation: DT: bindings: Add power domain info for NVIDIA PMC

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Date:	Tue, 08 Dec 2015 11:07:06 -0800
From:	Kevin Hilman <khilman@...nel.org>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Philipp Zabel <p.zabel@...gutronix.de>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	Rafael Wysocki <rjw@...ysocki.net>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Vince Hsu <vinceh@...dia.com>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH V4 12/16] Documentation: DT: bindings: Add power domain info for NVIDIA PMC

Jon Hunter <jonathanh@...dia.com> writes:

> Add power-domain binding documentation for the NVIDIA PMC driver in
> order to support generic power-domains.
>
> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
>
> ---
>
> Please note that I have been debating whether I add this
> "nvidia,powergate-clock-disable" property or just leave the clocks
> disabled by default. Some downstream kernels leave the clocks enabled
> for the audio power-domain because the clocks required for powering up
> the power-domain are needed by all modules within the power-domain.
> However are the same time there are other power-domains that may need
> to be on, but not always clocked and so having the ability to specify if
> the clocks should be disabled seems useful. However, I can also remove
> this and just have the appropriate devices turn on the clocks as well.
> ---
>  .../bindings/arm/tegra/nvidia,tegra20-pmc.txt      | 61 ++++++++++++++++++++++
>  1 file changed, 61 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt
> index 838e1a69ec0a..8e4641db51a9 100644
> --- a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt
> +++ b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt
> @@ -1,5 +1,7 @@
>  NVIDIA Tegra Power Management Controller (PMC)
>  
> +== Power Management Controller Node ==
> +
>  The PMC block interacts with an external Power Management Unit. The PMC
>  mostly controls the entry and exit of the system from different sleep
>  modes. It provides power-gating controllers for SoC and CPU power-islands.
> @@ -69,6 +71,10 @@ Optional properties for hardware-triggered thermal reset (inside 'i2c-thermtrip'
>                       Defaults to 0. Valid values are described in section 12.5.2
>                       "Pinmux Support" of the Tegra4 Technical Reference Manual.
>  
> +Optional nodes:
> +- pm-domains : This node contains a hierarchy of PM domain nodes, which should
> +	       match the power-domains on the Tegra SoC.
> +
>  Example:
>  
>  / SoC dts including file
> @@ -114,3 +120,58 @@ pmc@...0f400 {
>  	};
>  	...
>  };
> +
> +
> +== PM Domain Nodes ==
> +
> +Each of the PM domain nodes represents a power-domain on the Tegra SoC
> +that can be power-gated by the PMC and should be named appropriately.
> +
> +Required properties:
> +  - clocks: Must contain an entry for each clock required by the PMC for
> +    controlling a power-gate. See ../clocks/clock-bindings.txt for details.

We've had this discussiona for a couple of other SoCs, so I need to
ask...

Presumably these are not device clocks that a runtime PM enabled driver
should be managing for a device, right?  IOW, We want to make sure that the
PM domain isn't managing clocks for drivers that should be doing it.

I understand there are legitimate reasons for the PM domain to manage
clocks in addition to device drivers (e.g. for synchronous reset), but
just want to be sure it's not a shortcut for having a proper driver.

Kevin
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