acpi_spmc(4): Check DSMs only on attach, do not return 0 on probe

Once we have recognized a device by PNP ID, declare support
unconditionally on probe, and only check for DSMs in attach.

We do this for these reasons:
1. PNP0D80 is de-facto a device supposed to hold DSMs related to
   suspend-to-idle, so we assume it cannot be used for other purposes.
   And if that changes, we need another architecture anyway (e.g., have
   a new driver claiming those devices and behaving like a bus, to which
   this driver would be a sub-driver).
2. If there are no DSMs that we support on such a device, then a new DSM
   was added that the driver does not know about and which "replaces"
   (in terms of functionality) the known ones, or the firmware is buggy.
   In both cases, failing the attach instead of the probe is reasonable,
   as that leads to printing some error which we (and probably users
   too) would like to know about.
3. This is a step to enable multiple instances of this driver (just to
   be a good citizen, and also to be future proof against weird
   firmwares that would, e.g., implement the Microsoft DSM on another
   device than the Intel one).

Reviewed by:    imp (older version), obiwac
Sponsored by:   The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D56810

sys/dev/acpica/acpi_spmc.c

@@ -340,10 +340,7 @@ static void	acpi_spmc_resume(device_t dev, enum power_stype stype);
 static int
 acpi_spmc_probe(device_t dev)
 {
-	char			*name;
-	ACPI_HANDLE		 handle;
-	struct acpi_spmc_softc	*sc;
-	char			 buf[32];
+	char *name;
 
 	/* Check that this is an enabled device. */
 	if (acpi_get_type(dev) != ACPI_TYPE_DEVICE || acpi_disabled("spmc"))
@@ -357,41 +354,42 @@ acpi_spmc_probe(device_t dev)
 		return (ENXIO);
 	}
 
-	handle = acpi_get_handle(dev);
-	/* ACPI_ID_PROBE() above cannot succeed without a handle. */
-	MPASS(handle != NULL);
+	device_set_desc(dev, "System Power Management Controller");
 
-	sc = device_get_softc(dev);
-	sc->dev = dev;
-
-	/* Check which DSMs are supported. */
-	sc->dsms = 0;
-
-	for (int i = 0; i < nitems(dsms); ++i)
-		acpi_spmc_check_dsm(sc, handle, dsms[i]);
-
-	if (sc->dsms == 0)
-		return (ENXIO);
-
-	print_bit_field(buf, sizeof(buf), sc->dsms, "DSM", pbf_dsm_name, NULL);
-	device_set_descf(dev, "System Power Management Controller (DSMs %s)",
-	    buf);
-
-	return (0);
+	return (BUS_PROBE_DEFAULT);
 }
 
 static int
 acpi_spmc_attach(device_t dev)
 {
-	struct acpi_spmc_softc *sc = device_get_softc(dev);
+	struct acpi_spmc_softc *const sc = device_get_softc(dev);
+	const ACPI_HANDLE handle = acpi_get_handle(dev);
+	char buf[32];
 
-	sc->handle = acpi_get_handle(dev);
-	if (sc->handle == NULL)
+	/*
+	 * ACPI_ID_PROBE() in acpi_spmc_probe() cannot succeed without a handle.
+	 */
+	MPASS(handle != NULL);
+
+	sc->dev = dev;
+	sc->handle = handle;
+
+	for (int i = 0; i < nitems(dsms); ++i) {
+		KASSERT(dsms[i] != NULL, ("%s: Sparse dsms[]!", __func__));
+		KASSERT(dsms[i]->index == i,
+		    ("%s: Inconsistent indices for DSM %s", __func__,
+		    dsms[i]->name));
+
+		acpi_spmc_check_dsm(sc, handle, dsms[i]);
+	}
+
+	if (sc->dsms == 0) {
+		device_printf(dev, "No DSM supported!");
 		return (ENXIO);
+	}
 
-	sc->constraints_populated = false;
-	sc->constraint_count = 0;
-	sc->constraints = NULL;
+	print_bit_field(buf, sizeof(buf), sc->dsms, "DSM", pbf_dsm_name, NULL);
+	device_printf(dev, "DSMs supported: %s\n", buf);
 
 	/* Get device constraints. We can only call this once so do this now. */
 	acpi_spmc_get_constraints(dev);