asmc: try PIO before MMIO to avoid false T2 detection

Add hw.asmc.system-state and hw.asmc.board-id read-only sysctls to
expose the T2 system state register and Mac board identifier via SMC.

Try PIO access before MMIO during probe to prevent false T2 detection
on Macs that happen to have something mapped at the T2 BAR address.

Reviewed by:	adrian
Differential Revision:	https://reviews.freebsd.org/D57844

3 files changed, 33 insertions, 26 deletions

diff --git a/sys/dev/asmc/asmc.c b/sys/dev/asmc/asmc.c
index 055f98e06892..1796867786e5 100644
--- a/sys/dev/asmc/asmc.c
+++ b/sys/dev/asmc/asmc.c
@@ -418,43 +418,50 @@ asmc_probe(device_t dev)
 	return (rv);
 }
 
+/*
+ * Try PIO first; fall back to MMIO for T2 Macs.
+ */
 static int
-asmc_attach(device_t dev)
+asmc_try_probe(device_t dev)
 {
-	int i, j;
-	int ret;
-	char name[2];
 	struct asmc_softc *sc = device_get_softc(dev);
-	struct sysctl_ctx_list *sysctlctx;
-	struct sysctl_oid *sysctlnode;
 
-	/*
-	 * Try MMIO first (T2 Macs expose SMC via memory-mapped I/O).
-	 * Fall back to standard I/O port if MMIO is not available.
-	 */
+	sc->sc_ioport = bus_alloc_resource_any(dev, SYS_RES_IOPORT,
+	    &sc->sc_rid_port, RF_ACTIVE);
+	if (sc->sc_ioport != NULL)
+		return (0);
+
 	sc->sc_rid_mem = 0;
 	sc->sc_iomem = bus_alloc_resource_any(dev, SYS_RES_MEMORY,
 	    &sc->sc_rid_mem, RF_ACTIVE);
 	if (sc->sc_iomem != NULL) {
 		if (asmc_mmio_probe(dev) == 0) {
-			sc->sc_is_mmio = 1;
+			sc->sc_is_mmio = true;
 			device_printf(dev, "using MMIO backend (T2)\n");
-		} else {
-			bus_release_resource(dev, SYS_RES_MEMORY,
-			    sc->sc_rid_mem, sc->sc_iomem);
-			sc->sc_iomem = NULL;
+			return (0);
 		}
+		bus_release_resource(dev, SYS_RES_MEMORY,
+		    sc->sc_rid_mem, sc->sc_iomem);
+		sc->sc_iomem = NULL;
 	}
 
-	if (!sc->sc_is_mmio) {
-		sc->sc_ioport = bus_alloc_resource_any(dev, SYS_RES_IOPORT,
-		    &sc->sc_rid_port, RF_ACTIVE);
-		if (sc->sc_ioport == NULL) {
-			device_printf(dev, "unable to allocate IO port\n");
-			ret = ENOMEM;
-			goto err;
-		}
-	}
+	device_printf(dev, "unable to allocate IO port\n");
+	return (ENOMEM);
+}
+
+static int
+asmc_attach(device_t dev)
+{
+	int i, j;
+	int ret;
+	char name[2];
+	struct asmc_softc *sc = device_get_softc(dev);
+	struct sysctl_ctx_list *sysctlctx;
+	struct sysctl_oid *sysctlnode;
+
+	ret = asmc_try_probe(dev);
+	if (ret != 0)
+		goto err;
 
 	sysctlctx = device_get_sysctl_ctx(dev);
 	sysctlnode = device_get_sysctl_tree(dev);
diff --git a/sys/dev/asmc/asmcmmio.c b/sys/dev/asmc/asmcmmio.c
index 016c50f6170f..237e8ec4ed52 100644
--- a/sys/dev/asmc/asmcmmio.c
+++ b/sys/dev/asmc/asmcmmio.c
@@ -307,7 +307,7 @@ asmc_mmio_detach(device_t dev, struct asmc_softc *sc)
 		    sc->sc_iomem);
 		sc->sc_iomem = NULL;
 	}
-	sc->sc_is_mmio = 0;
+	sc->sc_is_mmio = false;
 	sc->sc_is_t2 = 0;
 }
 
diff --git a/sys/dev/asmc/asmcvar.h b/sys/dev/asmc/asmcvar.h
index bc0c624eb7a2..70485c32ea88 100644
--- a/sys/dev/asmc/asmcvar.h
+++ b/sys/dev/asmc/asmcvar.h
@@ -56,7 +56,7 @@ struct asmc_softc {
 	/* MMIO backend (T2 Macs) */
 	int			sc_rid_mem;
 	struct resource		*sc_iomem;
-	int			sc_is_mmio;
+	bool			sc_is_mmio;
 	int			sc_is_t2;	/* T2 fan float + per-fan manual */
 	int 			sc_sms_intrtype;
 	struct taskqueue 	*sc_sms_tq;