If we have multiple interrupt resources, like for Z8530 clones on the

mac-io bus, we cannot setup FAST interrupt handlers. This because we
use spinlocks to protect the hardware and all interrupt resources are
assigned the same interrupt handler. When the interrupt handler is
invoked for interrupt X, it could be preempted for interrupt Y while
it was holding the lock (where X and Y are the interrupt resources
corresponding a single instance of this driver). This is a deadlock.
By only using a MPSAFE handler in that case we prevent preemption.

1 files changed, 13 insertions, 11 deletions

diff --git a/sys/dev/scc/scc_core.c b/sys/dev/scc/scc_core.c
index c9cda51..1101f8a 100644
--- a/sys/dev/scc/scc_core.c
+++ b/sys/dev/scc/scc_core.c
@@ -102,7 +102,7 @@ scc_bfe_attach(device_t dev)
 	const char *sep;
 	bus_space_handle_t bh;
 	u_long base, size, start;
-	int c, error, mode, sysdev;
+	int c, error, mode, nintr, sysdev;
 
 	/*
 	 * The sc_class field defines the type of SCC we're going to work
@@ -140,11 +140,14 @@ scc_bfe_attach(device_t dev)
 	 */
 	sc->sc_chan = malloc(sizeof(struct scc_chan) * cl->cl_channels,
 	    M_SCC, M_WAITOK | M_ZERO);
+	nintr = 0;
 	for (c = 0; c < cl->cl_channels; c++) {
 		ch = &sc->sc_chan[c];
 		ch->ch_irid = c;
 		ch->ch_ires = bus_alloc_resource_any(dev, SYS_RES_IRQ,
 		    &ch->ch_irid, RF_ACTIVE | RF_SHAREABLE);
+		if (ch->ch_ires != NULL)
+			nintr++;
 	}
 
 	/*
@@ -210,16 +213,18 @@ scc_bfe_attach(device_t dev)
 	 * that our children's are fast as well. We make it MPSAFE as soon
 	 * as a child sets up a MPSAFE interrupt handler.
 	 * Of course, if we can't setup a fast handler, we make it MPSAFE
-	 * right away.
+	 * right away. If we have multiple interrupt resources, we don't
+	 * use fast handlers, because we need to serialize the interrupts.
 	 */
 	for (c = 0; c < cl->cl_channels; c++) {
 		ch = &sc->sc_chan[c];
 		if (ch->ch_ires == NULL)
 			continue;
-		error = bus_setup_intr(dev, ch->ch_ires,
-		    INTR_TYPE_TTY | INTR_FAST, scc_bfe_intr, sc,
-		    &ch->ch_icookie);
-		if (error) {
+		if (nintr == 1)
+			error = bus_setup_intr(dev, ch->ch_ires,
+			    INTR_TYPE_TTY | INTR_FAST, scc_bfe_intr, sc,
+			    &ch->ch_icookie);
+		if (nintr > 1 || error) {
 			error = bus_setup_intr(dev, ch->ch_ires,
 			    INTR_TYPE_TTY | INTR_MPSAFE, scc_bfe_intr, sc,
 			    &ch->ch_icookie);
@@ -231,13 +236,10 @@ scc_bfe_attach(device_t dev)
 			bus_release_resource(dev, SYS_RES_IRQ, ch->ch_irid,
 			    ch->ch_ires);
 			ch->ch_ires = NULL;
+			nintr--;
 		}
 	}
-	sc->sc_polled = 1;
-	for (c = 0; c < cl->cl_channels; c++) {
-		if (sc->sc_chan[0].ch_ires != NULL)
-			sc->sc_polled = 0;
-	}
+	sc->sc_polled = (nintr == 0) ? 1 : 0;
 
 	/*
 	 * Attach all child devices that were probed successfully.