linux-kernel - Re: [PATCH v2 1/5] of: Add descriptions of thermtrip properties to Tegra PMC bindings

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Date:	Wed, 20 Aug 2014 14:16:49 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Mikko Perttunen <mperttunen@...dia.com>, thierry.reding@...il.com
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-tegra@...r.kernel.org, wni@...dia.com
Subject: Re: [PATCH v2 1/5] of: Add descriptions of thermtrip properties to
 Tegra PMC bindings

On 08/13/2014 06:41 AM, Mikko Perttunen wrote:
> Hardware-triggered thermal reset requires configuring the I2C
> reset procedure. This configuration is read from the device tree,
> so document the relevant properties in the binding documentation.

> diff --git a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt

> +Hardware-triggered thermal reset:
> +On Tegra30, Tegra114 and Tegra124, if the 'i2c-thermtrip' subnode exists,
> +hardware-triggered thermal reset will be enabled.

"will be enabled" sounds like SW behaviour, whereas DT is suppose to 
describe HW, and leave SW to define its own behaviour. I would suggest:

Optional sub-nodes:
i2c-thermtrip: Describes how to power off the system in the event of a
   thermal emergency.

> +Required properties for hardware-triggered thermal reset (inside 'i2c-thermtrip'):

Simpler might be:

Required properties for i2c-thermtrip node:

> +- nvidia,pmu : Phandle to power management unit / PMIC handling poweroff
> +- nvidia,reg-addr : I2C register address to write poweroff command to
> +- nvidia,reg-data : Poweroff command to write to PMU

Why are both the PMU/PMIC phandle and the register address/data 
required? I thought the purpose of having the phandle was to allow the 
register address and data to be queried from the PMU/PMIC driver.

To me, it seems much simpler to get rid of the phandle and just 
hard-code the I2C bus number, address, and data into this node, rather 
than having to go query it from the PMU/PMIC driver, then find the I2C 
controller, then query it for its ID (and hope that all HW modules that 
talk to I2C controllers directly use the same numbering scheme...)
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