Question: device_t related code vs. FDT's lack of define before use/reference requirements: is there a normal FreeBSD technique to deal with such?

From: Mark Millard <marklmi_at_yahoo.com>
Date: Thu, 15 Dec 2022 22:29:21 UTC 
While the RPi4B's provide the example here, as far as
I can tell, nothing here need be RPi* specific: the
question is more general for FDT involvement in the
device_t related activity.

Modern RPi4B live FDT's have the sequencing:

		mmc@7e300000 {
			compatible = "brcm,bcm2835-mmc", "brcm,bcm2835-sdhci";
			. . .
			dmas = <0x0000000c 0x0000000b>;
			. . .
		};
. . .
. . . Note: the brcm,bcm2835-mmc related attach attempts to use the later dma@7e007000
. . .       instance of brcm,bcm2835-dma. (Note the 0x0000000c phandle referenced is
. . .       defined below as well: reference before definition.)
. . .       The result is a kernel crash from a bad dereference of bcm_dma_sc->sc_mtx
. . .       (really sc=bcm_dma_sc then later sc->sc_mtx).
. . .
		dma@7e007000 {
			compatible = "brcm,bcm2835-dma";
			. . .
			interrupt-names = "dma0", "dma1", "dma2", "dma3", "dma4", "dma5", "dma6", "dma7", "dma8", "dma9", "dma10";
			#dma-cells = <0x00000001>;
			brcm,dma-channel-mask = <0x000007f5>;
			phandle = <0x0000000c>;
		};
. . .
		mmcnr@7e300000 {
			compatible = "brcm,bcm2835-mmc", "brcm,bcm2835-sdhci";
			. . .
			dmas = <0x0000000c 0x0000000b>;
			dma-names = "rx-tx";
			. . .
		};

How is the device_t related probing and attachment of
FreeBSD devices supposed to work for such a FDT
ordering of the information? Are there one or more
identified ways of handling such?

Or does FreeBSD effectively require define before
use/reference in FDT's in general?
 

The code happened to not fail back when the RPi* firmware
happened to have the FDT sequencing (phandle 0x0000000b
for this example):

		dma@7e007000 {
			compatible = "brcm,bcm2835-dma";
			. . .
			interrupt-names = "dma0", "dma1", "dma2", "dma3", "dma4", "dma5", "dma6", "dma7", "dma8", "dma9", "dma10";
			#dma-cells = <0x00000001>;
			brcm,dma-channel-mask = <0x000007f5>;
			phandle = <0x0000000b>;
		};
. . .
		mmc@7e300000 {
			compatible = "brcm,bcm2835-mmc", "brcm,bcm2835-sdhci";
			. . .
			dmas = <0x0000000b 0x0000000b>;
			dma-names = "rx-tx";
			. . .
		};
		mmcnr@7e300000 {
			compatible = "brcm,bcm2835-mmc", "brcm,bcm2835-sdhci";
			. . .
			dmas = <0x0000000b 0x0000000b>;
			dma-names = "rx-tx";
			. . .
		};

(which happens to be: define before use/reference).

===
Mark Millard
marklmi at yahoo.com