When the initarm_* routines were renamed to platform_* and moved to their

own header file, the lovely block of comments explaining what the generic
init code expects of the soc implementations got lost, restore it.

sys/arm/include/platform.h

@@ -29,6 +29,34 @@
 #ifndef	_MACHINE_PLATFORM_H_
 #define	_MACHINE_PLATFORM_H_
 
+/*
+ * Initialization functions called by the common initarm() function in
+ * arm/machdep.c (but not necessarily from the custom initarm() functions of
+ * older code).
+ *
+ *  - platform_probe_and_attach() is called very early, after parsing the boot
+ *    params and after physical memory has been located and sized.
+ *
+ *  - platform_devmap_init() is called as one of the last steps of early virtual
+ *    memory initialization, shortly before the new page tables are installed.
+ *
+ *  - platform_lastaddr() is called after platform_devmap_init(), and must return
+ *    the address of the first byte of unusable KVA space.  This allows a
+ *    platform to carve out of the top of the KVA space whatever reserves it
+ *    needs for things like static device mapping, and this is called to get the
+ *    value before calling pmap_bootstrap() which uses the value to size the
+ *    available KVA.
+ *
+ *  - platform_gpio_init() is called after the static device mappings are
+ *    established and just before cninit().  The intention is that the routine
+ *    can do any hardware setup (such as gpio or pinmux) necessary to make the
+ *    console functional.
+ *
+ *  - platform_late_init() is called just after cninit().  This is the first of
+ *    the init routines that can use printf() and expect the output to appear on
+ *    a standard console.
+ *
+ */
 void platform_probe_and_attach(void);
 int platform_devmap_init(void);
 vm_offset_t platform_lastaddr(void);