Message-ID: <20140821165357.GC1172@ulmo>
Date:	Thu, 21 Aug 2014 18:53:58 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Mikko Perttunen <mperttunen@...dia.com>,
	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 Thu, Aug 21, 2014 at 09:38:29AM -0600, Stephen Warren wrote:
> On 08/21/2014 12:58 AM, Thierry Reding wrote:
> >On Wed, Aug 20, 2014 at 02:16:49PM -0600, Stephen Warren wrote:
> >>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...)
> >
> >I originally requested this to be changed. It seems wrong to duplicate
> >information about the PMIC in both the PMIC device tree node and the
> >i2c-thermtrip node if we can get the same information from the driver
> >directly (via the phandle). It certainly requires a little more code,
> >but at the advantage of not having to figure out the I2C controller
> >hardware number and I2C slave addresses when writing the i2c-thermtrip
> >node.
> 
> I cant see that argument, but surely the PMIC driver can also supply the
> "reg-addr" and "reg-data" values too, if it's already being queried for the
> I2C device address and bus number? The binding above appears to duplicate
> part of the information, while requiring querying of the other part.

I suppose that could be done. It would take a new function to do that,
though, since I'm not aware of a generic mechanism to query this kind of
information from a PMIC (there's no generic PMIC API, either, so perhaps
it would be a good time to create one?). The I2C controller and I2C
slave are generic I2C properties, whereas the register and data to power
off the device are very device specific.

Thierry

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