Nothing apart from only being used by arm64 platforms today, which is
circumstantial.

quoted

I understand you need to find a place to add the:

acpi_indirect_io_scan_init()

to be called from core ACPI code because ACPI can't handle probe
dependencies in any other way but other than that this patch is
a Hisilicon ACPI driver - there is nothing generic in it (or at
least there are no standard bindings to make it so).

Whether a callback from ACPI core code (acpi_scan_init()) to a driver
specific hook is sane or not that's the question and the only reason
why you want to add this in drivers/acpi/arm64 rather than, say,
drivers/bus (as you do for the DT driver).

I do not know Rafael's opinion on the above, I would like to help
you make forward progress but please understand my concerns, mostly
on FW side.

I did mention an alternative in my "ping" in v12 patch 7/9 (Feb 1), but
no response to this specific note so I kept on the same path.

Here's what I then wrote:
"I think another solution - which you may prefer - is to avoid adding
this scan handler (and all this other scan code) and add a check like
acpi_is_serial_bus_slave() [which checks the device parent versus a list
of known indirectIO hosts] to not enumerate these children, and do it
from the LLDD host probe instead (https://lkml.org/lkml/2017/6/16/250)"

Hi Rafael, Lorenzo,

I can avoid adding the scan handler in acpi_indirectio.c by skipping the 
child enumeration, like with this change in scan.c:

+static const struct acpi_device_id indirect_io_hosts[] = {
+    {"HISI0191", 0},    /* HiSilicon LPC host */
+    {},
+};
+
+static bool acpi_is_indirect_io_slave(struct acpi_device *device)
+{
+    struct acpi_device *parent = dev->parent;
+
+    if (!parent || acpi_match_device_ids(parent, indirect_io_hosts))
+        return false;
+
+    return true;
+}
+
  static bool acpi_is_serial_bus_slave(struct acpi_device *device)
  {
      struct list_head resource_list;
      bool is_serial_bus_slave = false;

+    if (acpi_is_indirect_io_slave(device))
+        return true;
+
      /* Macs use device properties in lieu of _CRS resources */


This means I can move all this scan code into the LLDD.

What do you think? Please let me know.

John