Allow device hints to wire the unit numbers of devices.

- An "at" hint now reserves a device name.
- A new BUS_HINT_DEVICE_UNIT method is added to the bus interface.  When
  determining the unit number of a device, this method is invoked to
  let the bus driver specify the unit of a device given a specific
  devclass.  This is the only way a device can be given a name reserved
  via an "at" hint.
- Implement BUS_HINT_DEVICE_UNIT() for the acpi(4) and isa(4) bus drivers.
  Both of these busses implement this by comparing the resources for a
  given hint device with the resources enumerated by ACPI/PnPBIOS and
  wire a unit if the hint resources are a subset of the "real" resources.
- Use bus_hinted_children() for adding hinted devices on isa(4) busses
  now instead of doing it by hand.
- Remove the unit kludging from sio(4) as it is no longer necessary.

Prodding from:	peter, imp
OK'd by:	marcel
MFC after:	1 month

1 files changed, 20 insertions, 4 deletions

diff --git a/sys/kern/subr_bus.c b/sys/kern/subr_bus.c
index 93a589a2..10fc81a 100644
--- a/sys/kern/subr_bus.c
+++ b/sys/kern/subr_bus.c
@@ -1315,12 +1315,18 @@ devclass_get_sysctl_tree(devclass_t dc)
  * @retval ENOMEM	memory allocation failure
  */
 static int
-devclass_alloc_unit(devclass_t dc, int *unitp)
+devclass_alloc_unit(devclass_t dc, device_t dev, int *unitp)
 {
+	const char *s;
 	int unit = *unitp;
 
 	PDEBUG(("unit %d in devclass %s", unit, DEVCLANAME(dc)));
 
+	/* Ask the parent bus if it wants to wire this device. */
+	if (unit == -1)
+		BUS_HINT_DEVICE_UNIT(device_get_parent(dev), dev, dc->name,
+		    &unit);
+
 	/* If we were given a wired unit number, check for existing device */
 	/* XXX imp XXX */
 	if (unit != -1) {
@@ -1334,8 +1340,18 @@ devclass_alloc_unit(devclass_t dc, int *unitp)
 	} else {
 		/* Unwired device, find the next available slot for it */
 		unit = 0;
-		while (unit < dc->maxunit && dc->devices[unit] != NULL)
-			unit++;
+		for (unit = 0;; unit++) {
+			/* If there is an "at" hint for a unit then skip it. */
+			if (resource_string_value(dc->name, unit, "at", &s) ==
+			    0)
+				continue;
+
+			/* If this device slot is already in use, skip it. */
+			if (unit < dc->maxunit && dc->devices[unit] != NULL)
+				continue;
+
+			break;
+		}
 	}
 
 	/*
@@ -1397,7 +1413,7 @@ devclass_add_device(devclass_t dc, device_t dev)
 	if (!dev->nameunit)
 		return (ENOMEM);
 
-	if ((error = devclass_alloc_unit(dc, &dev->unit)) != 0) {
+	if ((error = devclass_alloc_unit(dc, dev, &dev->unit)) != 0) {
 		free(dev->nameunit, M_BUS);
 		dev->nameunit = NULL;
 		return (error);