linux-kernel - Re: [PATCH 1/2] DT: add binding for mxs regulator

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Date:	Mon, 29 Sep 2014 13:53:22 +0200
From:	Stefan Wahren <stefan.wahren@...e.com>
To:	Mark Rutland <mark.rutland@....com>
CC:	"lgirdwood@...il.com" <lgirdwood@...il.com>,
	"broonie@...nel.org" <broonie@...nel.org>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"festevam@...il.com" <festevam@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: Re: [PATCH 1/2] DT: add binding for mxs regulator

Hi Mark,

Am 29.09.2014 um 13:09 schrieb Mark Rutland:
> On Sat, Sep 27, 2014 at 01:59:47AM +0100, Stefan Wahren wrote:
>> This patch adds the Device tree bindings for the Freescale MXS
>> on-chip regulators.
>>
>> Signed-off-by: Stefan Wahren <stefan.wahren@...e.com>
>> ---
>>  .../bindings/regulator/mxs-regulator.txt           |   36 ++++++++++++++++++++
>>  1 file changed, 36 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/regulator/mxs-regulator.txt
>>
>> diff --git a/Documentation/devicetree/bindings/regulator/mxs-regulator.txt b/Documentation/devicetree/bindings/regulator/mxs-regulator.txt
>> new file mode 100644
>> index 0000000..e3133a4
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/regulator/mxs-regulator.txt
>> @@ -0,0 +1,36 @@
>> +MXS regulators
>> +
>> +Required node properties:
>> +- compatible: Should be "simple-bus"
> This does not look like an appropriate use of simple-bus.
>
> Why do you want the parent node to be a simple-bus?

the current parent node in imx28.dtsi looks like a placeholder for the
power sub system:

power: power@...44000 {
	reg = <0x80044000 0x2000>;
	status = "disabled";
};

I want to trigger the probing of the child nodes (regulators) without
writing a driver for the complete power sub system. The simple-bus
avoids that.

Do we need a extra driver?

>
>> +- #address-cells: Number of cells required to define regulator register,
>> +  must be 1
>> +- #size-cells: Number of cells required to define register size, must be 1
> Why must this be the case, given that the child node expects an absolute
> physical address?

I need a property to define the control register for the regulators
without defining vendor specific properties like "fsl,mxs-control-reg"
or something.

> What's wrong with #address-cells = <2>, for example?

Nothing

>
>> +- reg: Absolute physical address and size of the register set for the device
> Why is this here _and_ in the child node(s)?

The parent of the power node is also a simple bus. I use this to
calculate the power status register per offset.

> What is the difference between this node and its children?

The parent node represent the power sub system and the regulators are
part of this sub system.

> Can there be more than one sub-node?

In the i.MX28 are at least 4 voltage regulators, 1 current regulator and
many more. At first, the driver should implement only 3 voltage
regulators (vddd, vdda, vddio).

> Mark.
>

Best regards

Stefan
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