dts: silabs: use 'aliases' to remove dts_fixup defines

[mnkp]

Following PR is a request for comments. The change is implemented for efr32fg1p SoC only.

By adding 'aliases' node in SoC .dtsi file it is possible to generate DT_ defines which specify a logical name rather than relay on a module location on APB bus. E.g. DT_SILABS_GECKO_USART_40010000_LABEL becomes DT_SILABS_GECKO_USART_USART_0_LABEL. Thus it is possible to remove dts_fixup.h defines. There is no limit on adding aliases for a given node and user is free to add a different one. Nordic family SoCs use the same approach.

Another possibility to avoid adding dts_fixup entries is to modify the script which generates DT_ defines. A DTS node is defined as

[label:] node-name[@unit-address] {
	[properties definitions]
	[child nodes]
}

e.g.

usart0: usart@40010000 { /* USART0 */
		[...]
};

where usart0 is a node label. If a script used a node label rather than a unit address the resulting defines would relay on logical names and not on part number dependent, fixed addresses. However, since this approach was not implemented by maintainers of DTS scripts there may be a good reason to avoid it.

[mnkp]

@ekarlso, @diegosueiro, @mtuxpe I've prepared another PR as an RFC with a goal to remove reliance on dts_fixup.h file. The change was done for efr32fg1p series only. If this approach is accepted remaining SiLabs series would also need to be updated. Your comments are welcome.

[diegosueiro]

The USART string repetition in the generated #define seems unnecessary to me.
@galak, is there a way to avoid this?

[mnkp]

This pattern was established by #11180. The first part 'SILABS_GECKO_USART' is equal to the 'compatible' property of the node for which the define is generated. What follows is the extracted property itself.

One could argue that this is not the right choice for the define generated from an alias node since according to the device tree specification "The alias node shall be at the root of the devicetree". That means it belongs to the global namespace.

[diegosueiro]

@mnkp,

I definitely agree on using aliases over dts_fixup. It is just strange for me (almost hurt my eyes) seeing this string repetitions.

[codecov-io]

Codecov Report

Merging #11707 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #11707   +/-   ##
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  Coverage    48.2%    48.2%           
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  Files         280      280           
  Lines       43323    43323           
  Branches    10374    10374           
=======================================
  Hits        20886    20886           
  Misses      18289    18289           
  Partials     4148     4148

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[chrta]

I have one question, maybe related to this. I plan to implement an spi driver that uses the usart peripheral.
In the device tree, this could use the same base node, e.g. usart@40010000, right?

[mnkp]

Yes, DTS describes underlying hardware and its structure. Since both drivers use the same hardware module they will use the same dts node.

One example that I know of where the same hardware module is used by several drivers is sercom peripheral on Atmel SAMD21 device. Best place to start looking into the code is here.

[chrta]

Thank you

[chrta]

I prefer using aliases over dts_fixup.h

[mnkp]

I've pushed a new version that implements required changes for all SiLabs SoCs and boards. This PR is now suitable for merging.

I confirmed that all SiLabs boards compile with no error. However, some more testing would definitely be welcomed. Especially verifying that i2c, usart, uart, leuart modules work in real life on the board.

[mnkp]

@galak, @MaureenHelm The discussion regarding the best method to remove dts_fixup files is still ongoing, however the aliases are already used by the Nordic SoCs. Even if we choose to handle generation of DTS defines differently it's easier to update defines within a few device drivers rather than maintain dts_fixup files. Could we review and merge this PR?