Preprocessor arithmetic in dtsi files (base + offset)

Preprocessor arithmetic in dtsi files (base + offset)

[Mason]

Hello,

In the device tree for my ARM platform, I have several nodes with
addresses within the SCU block:

	scu: scu@20000000 {
		compatible = "arm,cortex-a9-scu";
		reg = <0x20000000 0x100>;

	gic: interrupt-controller@20001000 {
		compatible = "arm,cortex-a9-gic";
		reg = <0x20001000 0x1000>, <0x20000100 0x0100>;

	twd-timer@20000600 {
		compatible = "arm,cortex-a9-twd-timer";
		reg = <0x20000600 0x10>;

Can I use preprocessor arithmetic to abstract the base address,
as would be done in C?

#define SCU_BASE 0x20000000

	scu: scu@XXX {
		compatible = "arm,cortex-a9-scu";
		reg = <SCU_BASE 0x100>;
	
	gic: interrupt-controller@XXX {
		compatible = "arm,cortex-a9-gic";
		reg = <SCU_BASE+0x1000 0x1000>, <SCU_BASE+0x100 0x0100>;

	twd-timer@XXX {
		compatible = "arm,cortex-a9-twd-timer";
		reg = <SCU_BASE+0x600 0x10>;

Are the @XXX important? Can they be removed altogether?

Regards.
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Re: Preprocessor arithmetic in dtsi files (base + offset)

[Mark Rutland]

On Thu, Nov 26, 2015 at 02:16:16PM +0100, Mason wrote:
> Hello,
> 
> In the device tree for my ARM platform, I have several nodes with
> addresses within the SCU block:
> 
> 	scu: scu@20000000 {
> 		compatible = "arm,cortex-a9-scu";
> 		reg = <0x20000000 0x100>;
> 
> 	gic: interrupt-controller@20001000 {
> 		compatible = "arm,cortex-a9-gic";
> 		reg = <0x20001000 0x1000>, <0x20000100 0x0100>;
> 
> 	twd-timer@20000600 {
> 		compatible = "arm,cortex-a9-twd-timer";
> 		reg = <0x20000600 0x10>;
> 
> Can I use preprocessor arithmetic to abstract the base address,
> as would be done in C?
> 
> #define SCU_BASE 0x20000000
> 
> 	scu: scu@XXX {
> 		compatible = "arm,cortex-a9-scu";
> 		reg = <SCU_BASE 0x100>;
> 	
> 	gic: interrupt-controller@XXX {
> 		compatible = "arm,cortex-a9-gic";
> 		reg = <SCU_BASE+0x1000 0x1000>, <SCU_BASE+0x100 0x0100>;

The pre-processor would only do substitution, not arithmetic. So the '+'
would flow all the way to DTC.

DTC does have some basic integer expression support (see [1]), but it
looks like it can only work at the cell level, so generally it needs to
be avoided (in case #address-cells >1, for example).

So generally I think that such arithmetic should be avoided.

> 	twd-timer@XXX {
> 		compatible = "arm,cortex-a9-twd-timer";
> 		reg = <SCU_BASE+0x600 0x10>;
> 
> Are the @XXX important? Can they be removed altogether?

The bit after the @ is called the unit-address.

It's meant to be there (matching the base address of the first reg
entry) to disambiguate nodes and make it simple to figure out where a
node lives in the physical address space.

They should stay.

Thanks,
Mark.

[1] https://git.kernel.org/cgit/linux/kernel/git/jdl/dtc.git/commit/?id=5f0c3b2d6235dec65fff1628a97f45e21680b36d
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Re: Preprocessor arithmetic in dtsi files (base + offset)

[Russell King - ARM Linux]

On Thu, Nov 26, 2015 at 02:16:16PM +0100, Mason wrote:
> #define SCU_BASE 0x20000000
> 
> 	scu: scu@XXX {
> 		compatible = "arm,cortex-a9-scu";
> 		reg = <SCU_BASE 0x100>;
> 	
> 	gic: interrupt-controller@XXX {
> 		compatible = "arm,cortex-a9-gic";
> 		reg = <SCU_BASE+0x1000 0x1000>, <SCU_BASE+0x100 0x0100>;

You don't get preprocessor arithmetic here.  What you get is this passed
to DTC:

		reg = <0x20000000+0x1000 0x1000>...

The only time the preprocessor does arithmetic is when it needs to
evaluate an expression, eg, in an #if statement.

The @XXX are part of the requirements from ePAPR, and are required to
be conformant with the spec.

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Re: Preprocessor arithmetic in dtsi files (base + offset)

[Mason]

On 26/11/2015 14:59, Russell King - ARM Linux wrote:
> On Thu, Nov 26, 2015 at 02:16:16PM +0100, Mason wrote:
>> #define SCU_BASE 0x20000000
>>
>> 	scu: scu@XXX {
>> 		compatible = "arm,cortex-a9-scu";
>> 		reg = <SCU_BASE 0x100>;
>> 	
>> 	gic: interrupt-controller@XXX {
>> 		compatible = "arm,cortex-a9-gic";
>> 		reg = <SCU_BASE+0x1000 0x1000>, <SCU_BASE+0x100 0x0100>;
> 
> You don't get preprocessor arithmetic here.  What you get is this passed
> to DTC:
> 
> 		reg = <0x20000000+0x1000 0x1000>...
> 
> The only time the preprocessor does arithmetic is when it needs to
> evaluate an expression, eg, in an #if statement.

Doh! Brain malfunction. No arithmetic indeed.
Working with the preprocessor would have to involve token-pasting.

#define SCU_BASE(OFFSET)	2000##OFFSET
#define SCU_BASEX(OFFSET)	0x2000##OFFSET

	gic: interrupt-controller@SCU_BASE(1000) {
		reg = <SCU_BASEX(1000) 0x1000>, <SCU_BASEX(0100) 0x0100>;
	};

My very own abomination!

Regards.

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Re: Preprocessor arithmetic in dtsi files (base + offset)

[Geert Uytterhoeven]

On Thu, Nov 26, 2015 at 3:44 PM, Mason <slash.tmp-GANU6spQydw@public.gmane.org> wrote:
> On 26/11/2015 14:59, Russell King - ARM Linux wrote:
>> On Thu, Nov 26, 2015 at 02:16:16PM +0100, Mason wrote:
>>> #define SCU_BASE 0x20000000
>>>
>>>      scu: scu@XXX {
>>>              compatible = "arm,cortex-a9-scu";
>>>              reg = <SCU_BASE 0x100>;
>>>
>>>      gic: interrupt-controller@XXX {
>>>              compatible = "arm,cortex-a9-gic";
>>>              reg = <SCU_BASE+0x1000 0x1000>, <SCU_BASE+0x100 0x0100>;
>>
>> You don't get preprocessor arithmetic here.  What you get is this passed
>> to DTC:
>>
>>               reg = <0x20000000+0x1000 0x1000>...
>>
>> The only time the preprocessor does arithmetic is when it needs to
>> evaluate an expression, eg, in an #if statement.
>
> Doh! Brain malfunction. No arithmetic indeed.
> Working with the preprocessor would have to involve token-pasting.
>
> #define SCU_BASE(OFFSET)        2000##OFFSET
> #define SCU_BASEX(OFFSET)       0x2000##OFFSET
>
>         gic: interrupt-controller@SCU_BASE(1000) {
>                 reg = <SCU_BASEX(1000) 0x1000>, <SCU_BASEX(0100) 0x0100>;
>         };
>
> My very own abomination!

Yeah! ;-)

I guess this would work, too?

scu_container@20000000 {
        compatible = "simple-bus";

        ranges = <0x0 0x20000000 0x10000>;
        #address-cells = <1>;
        #size-cells = <1>;

        scu: scu@0 {
                compatible = "arm,cortex-a9-scu";
                reg = <0x0000 0x100>;

        gic: interrupt-controller@1000 {
                compatible = "arm,cortex-a9-gic";
                reg = <0x1000 0x1000>, <0x0100 0x0100>;

        twd-timer@0600 {
                compatible = "arm,cortex-a9-twd-timer";
                reg = <0x0600 0x10>;
};

No more explicit arithmetic needed, just substitue "20000000".

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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Re: Preprocessor arithmetic in dtsi files (base + offset)

[Robin Murphy]

On 26/11/15 16:23, Geert Uytterhoeven wrote:
[...]
> I guess this would work, too?
>
> scu_container@20000000 {
>          compatible = "simple-bus";
>
>          ranges = <0x0 0x20000000 0x10000>;
>          #address-cells = <1>;
>          #size-cells = <1>;
>
>          scu: scu@0 {
>                  compatible = "arm,cortex-a9-scu";
>                  reg = <0x0000 0x100>;
>
>          gic: interrupt-controller@1000 {
>                  compatible = "arm,cortex-a9-gic";
>                  reg = <0x1000 0x1000>, <0x0100 0x0100>;
>
>          twd-timer@0600 {
>                  compatible = "arm,cortex-a9-twd-timer";
>                  reg = <0x0600 0x10>;
> };
>
> No more explicit arithmetic needed, just substitue "20000000".

Which, funnily enough, ends up looking an awful lot like the definition 
in the hardware documentation[1] too ;)

Robin.

[1]:http://infocenter.arm.com/help/topic/com.arm.doc.ddi0407i/CACCJFCJ.html

> Gr{oetje,eeting}s,
>
>                          Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                  -- Linus Torvalds
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>

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Re: Preprocessor arithmetic in dtsi files (base + offset)

[Mason]

On 26/11/2015 17:23, Geert Uytterhoeven wrote:

> I guess this would work, too?
> 
> scu_container@20000000 {
>         compatible = "simple-bus";
> 
>         ranges = <0x0 0x20000000 0x10000>;
>         #address-cells = <1>;
>         #size-cells = <1>;
> 
>         scu: scu@0 {
>                 compatible = "arm,cortex-a9-scu";
>                 reg = <0x0000 0x100>;
> 
>         gic: interrupt-controller@1000 {
>                 compatible = "arm,cortex-a9-gic";
>                 reg = <0x1000 0x1000>, <0x0100 0x0100>;
> 
>         twd-timer@0600 {
>                 compatible = "arm,cortex-a9-twd-timer";
>                 reg = <0x0600 0x10>;
> };
> 
> No more explicit arithmetic needed, just substitute "20000000".

I like it! Only one address to change in the next chip.
Minimizes the risk of missing something.

(I see that armada did something similar, but they also grouped
unrelated stuff. And bcm5301x did exactly what you suggested.)

Wondering if there are macro definitions for the intra-SCU offsets?
So I could have symbolic names, such as

  twd-timer@0600 {
    reg = <TWD_OFFSET 0x10>

Didn't see anything appropriate in include and arch/arm.
Should I include my own definitions at the top of the dtsi?

Regards.

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