RE: [PATCH 1/4] documentation: add palmas dts definition

[J, KEERTHY]

Hello Stephen,

Thanks for a detailed review.

> -----Original Message-----
> From: Stephen Warren [mailto:swarren@xxxxxxxxxxxxx]
> Sent: Thursday, February 28, 2013 12:03 AM
> To: J, KEERTHY
> Cc: grant.likely@xxxxxxxxxxxx; rob.herring@xxxxxxxxxxx;
> rob@xxxxxxxxxxx; devicetree-discuss@xxxxxxxxxxxxxxxx; linux-
> doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Cousson, Benoit;
> gg@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH 1/4] documentation: add palmas dts definition
> 
> On 02/17/2013 10:11 PM, J Keerthy wrote:
> > Add the DTS definition for the palmas device including the MFD
> children.
> ...
> > diff --git a/Documentation/devicetree/bindings/mfd/palmas.txt
> > b/Documentation/devicetree/bindings/mfd/palmas.txt
> ...
> > +Texas Instruments Palmas family
> > +
> > +The Palmas familly are Integrated Power Management Chips.
> > +These chips are connected to an i2c bus.
> 
> s/familly/family.

I will correct this.

> 
> > +
> > +Required properties:
> > +- compatible : Must be "ti,palmas";
> 
> Do you need a version number there; will there be Palmas v1 HW, then
> later Palmas v2 HW, and so on?

AFAIK there is no HW version.
 
> 
> > +  For Integrated power-management in the palmas series, twl6035,
> > + twl6037,
> > +  tps65913
> 
> If this binding represents multiple different chips, compatible should
> contain both the most chip-specific value (e.g. ti,twl6035 I guess
> given the above) /and/ the more generic "ti,palmas" value. This will
> allow any device-specific quirks to be implemented if needed in the
> future, without having to retrofit the device-specific compatible value
> into .dts files after the fact.

Ok.

> 
> > +- interrupts : This i2c device has an IRQ line connected to the main
> > +SoC
> > +- interrupt-controller : Since the palmas support several interrupts
> > +internally,
> > +  it is considered as an interrupt controller cascaded to the SoC
> one.
> > +- #interrupt-cells = <1>;
> 
> Why not 2; can't any IRQ flags be represented in DT? 1 seems limiting
> here unless the HW truly can't support configuration of IRQ input
> polarity of edge-vs-level sensitivity.

>From the register manual I see that only GPIO has the edge detect capability.
I agree.

> 
> > +- interrupt-parent : The parent interrupt controller.
> > +
> > +Optional node:
> > +- Child nodes contain in the palmas. The palmas family is made of
> > +several
> > +  variants that support a different number of features.
> > +  The child nodes will thus depend of the capability of the variant.
> 
> Are there DT bindings for those child nodes anywhere?
> 
> Representing each internal component as a separate DT node feels a
> little like designing the DT bindings to model the Linux-internal MFD
> structure. DT bindings should be driven by the HW design and OS-
> agnostic.
> 
> From a DT perspective, is there any need at all to create a separate DT
> node for each component? This would only be needed or useful if the
> child IP blocks (and hence DT bindings for those blocks) could be re-
> used in other top-level devices that aren't represented by this top-
> level ti,palmas DT binding. Are the HW IP blocks here re-used anywhere,
> or will they be?
>

I guess for now I will drop this patch and will be taken up once we
Finalize on the design.
 
> ...
> > +Example:
> > +/*
> > + * Integrated Power Management Chip Palmas  */
> > +palmas@48 {
> 
> There's a considerable mix of TAB and space indentation in this
> example.
> 
> > +    compatible = "ti,palmas";
> > +    reg = <0x48>;
> > +    interrupts = <39>; /* IRQ_SYS_1N cascaded to gic */
> 
> If that's routed to a regular ARM GIC, then I think you need extra
> cells there; #interrupt-cells=<3> for the ARM GIC.
> 
> > +    interrupt-controller;
> > +    #interrupt-cells = <1>;
> > +    interrupt-parent = <&gic>;
> > +    #address-cells = <1>;
> > +    #size-cells = <0>;
> > +
> > +	ti,mux-pad1 = <0x00>;
> > +	ti,mux-pad2 = <0x00>;
> > +	ti,power-ctrl = <0x03>;
> > +
> > +	palmas_pmic {
> 
> Just "pmic" seems simpler, although I dare say the node name isn't
> really used for anything.
> 
> > +		compatible = "ti,palmas_pmic";
> 
> Using _ in compatible values isn't common. "ti,palmas-pmic" instead?
> 
> > +		regulators {
> > +			smps12_reg: smps12 {
> 
> As I mentioned elsewhere, this binding (or a separate binding doc for
> "ti,palmas_pmic") should contain a list of valid values for these node
> names.
> 
> > +				regulator-min-microvolt = < 600000>;
> > +                regulator-max-microvolt = <1500000>;
> > +				regulator-always-on;
> > +				regulator-boot-on;
> > +                ti,warm-sleep = <0>;
> > +                ti,roof-floor = <0>;
> > +                ti,mode-sleep = <0>;
> > +                ti,warm-reset = <0>;
> > +                ti,tstep = <0>;
> > +                ti,vsel = <0>;
> > +			};
> > +		};
> > +		ti,ldo6-vibrator = <0>;
> > +	};
> > +
> > +    palmas_rtc {
> > +        compatible = "ti,palmas_rtc";
> > +        interrupts = <8 9>;
> 
> Are the interrupt outputs of the RTC fed directly to the GIC interrupt
> mentioned in the top-level Palmas node, or do these interrupts feed
> into a top-level IRQ controller in the Palmas device, which then feeds
> into the external IRQ controller?
> 
> If these feed into an on-chip IRQ controller, then you'd need an
> interrupt-parent property here to indicate that.
> 
> If these feed directly into an external IRQ controller, it's almost
> certain that IRQ controller's binding uses #interrupt-cells = <3> it
> is's the ARM GIC, and hence you need some extra cells here.
> 
> > +        reg = <0>;
> > +    };
> > +};

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