linux-kernel - Re: [PATCH v7 01/16] clk: tegra: Add binding for the Tegra124 DFLL clocksource

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Message-ID: <54E19804.9080003@iki.fi>
Date:	Mon, 16 Feb 2015 09:11:00 +0200
From:	Tuomas Tynkkynen <tuomas.tynkkynen@....fi>
To:	Thierry Reding <thierry.reding@...il.com>,
	Mikko Perttunen <mikko.perttunen@...si.fi>
CC:	swarren@...dotorg.org, gnurou@...il.com, pdeschrijver@...dia.com,
	rjw@...ysocki.net, viresh.kumar@...aro.org, mturquette@...aro.org,
	pwalmsley@...dia.com, vinceh@...dia.com, pgaikwad@...dia.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	tuomas.tynkkynen@....fi, Tuomas Tynkkynen <ttynkkynen@...dia.com>
Subject: Re: [PATCH v7 01/16] clk: tegra: Add binding for the Tegra124 DFLL
 clocksource

On 02/13/2015 12:42 AM, Thierry Reding wrote:
> On Thu, Jan 08, 2015 at 03:22:04PM +0200, Mikko Perttunen wrote:
>> From: Tuomas Tynkkynen <ttynkkynen@...dia.com>
>>
>> The DFLL is the main clocksource for the fast CPU cluster on Tegra124
>> and also provides automatic CPU rail voltage scaling as well. The DFLL
>> is a separate IP block from the usual Tegra124 clock-and-reset
>> controller, so it gets its own node in the device tree.
>>
>> Signed-off-by: Tuomas Tynkkynen <ttynkkynen@...dia.com>
>> Signed-off-by: Mikko Perttunen <mikko.perttunen@...si.fi>
>> ---
>>   .../bindings/clock/nvidia,tegra124-dfll.txt        | 69 ++++++++++++++++++++++
>>   1 file changed, 69 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/clock/nvidia,tegra124-dfll.txt
>>
...
>> +Required properties:
>> +- compatible : should be "nvidia,tegra124-dfll-fcpu"
>> +- reg : Defines the following set of registers, in the order listed:
>> +        - registers for the DFLL control logic.
>> +        - registers for the I2C output logic.
>> +        - registers for the integrated I2C master controller.
>> +        - look-up table RAM for voltage register values.
>
> Why do these all need to be separate sets? According to the TRM this is
> a single IP block with a single register region, why the need to split
> them apart?

On Tegra132, some of those register blocks (IIRC the first one) has 
moved to a different place (somewhere in the CAR register area). The TRM 
description indeed gives a single list of registers for the Tegra124 
implementation of the DFLL. The split into 4 blocks was to make the 
binding more future-proof and to be closer to the real hardware design.
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