Fix numerous issues in iic(4) and iicbus(4):

--Allow multiple open iic fds by storing addressing state in cdevpriv
--Fix, as much as possible, the baked-in race conditions in the iic
ioctl interface by requesting bus ownership on I2CSTART, releasing it on
I2CSTOP/I2CRSTCARD, and requiring bus ownership by the current cdevpriv
to use the I/O ioctls
--Reduce internal iic buffer size and remove 1K read/write limit by
iteratively calling iicbus_read/iicbus_write
--Eliminate dynamic allocation in I2CWRITE/I2CREAD
--Move handling of I2CRDWR to separate function and improve error handling
--Add new I2CSADDR ioctl to store address in current cdevpriv so that
I2CSTART is not needed for read(2)/write(2) to work
--Redesign iicbus_request_bus() and iicbus_release_bus():
    --iicbus_request_bus() no longer falls through if the bus is already
owned by the requesting device.  Multiple threads on the same device may
want exclusive access.  Also, iicbus_release_bus() was never
device-recursive anyway.
    --Previously, if IICBUS_CALLBACK failed in iicbus_release_bus(), but
the following iicbus_poll() call succeeded, IICBUS_CALLBACK would not be
issued again
    --Do not hold iicbus mtx during IICBUS_CALLBACK call.  There are
several drivers that may sleep in IICBUS_CALLBACK, if IIC_WAIT is passed.
    --Do not loop in iicbus_request_bus if IICBUS_CALLBACK returns
EWOULDBLOCK; instead pass that to the caller so that it can retry if so
desired.

Differential Revision:	https://reviews.freebsd.org/D2140
Reviewed by:	imp, jhb, loos
Approved by:	kib (mentor)

1 files changed, 39 insertions, 32 deletions

diff --git a/sys/dev/iicbus/iiconf.c b/sys/dev/iicbus/iiconf.c
index 940760b..09edb39 100644
--- a/sys/dev/iicbus/iiconf.c
+++ b/sys/dev/iicbus/iiconf.c
@@ -71,7 +71,6 @@ iicbus_poll(struct iicbus_softc *sc, int how)
 
 	default:
 		return (EWOULDBLOCK);
-		break;
 	}
 
 	return (error);
@@ -90,31 +89,32 @@ iicbus_request_bus(device_t bus, device_t dev, int how)
 	struct iicbus_softc *sc = (struct iicbus_softc *)device_get_softc(bus);
 	int error = 0;
 
-	/* first, ask the underlying layers if the request is ok */
 	IICBUS_LOCK(sc);
-	do {
-		error = IICBUS_CALLBACK(device_get_parent(bus),
-						IIC_REQUEST_BUS, (caddr_t)&how);
-		if (error)
-			error = iicbus_poll(sc, how);
-	} while (error == EWOULDBLOCK);
 
-	while (!error) {
-		if (sc->owner && sc->owner != dev) {
-
-			error = iicbus_poll(sc, how);
-		} else {
-			sc->owner = dev;
+	while ((error == 0) && (sc->owner != NULL))
+		error = iicbus_poll(sc, how);
+
+	if (error == 0) {
+		sc->owner = dev;
+		/* 
+		 * Drop the lock around the call to the bus driver. 
+		 * This call should be allowed to sleep in the IIC_WAIT case.
+		 * Drivers might also need to grab locks that would cause LOR
+		 * if our lock is held.
+		 */
+		IICBUS_UNLOCK(sc);
+		/* Ask the underlying layers if the request is ok */
+		error = IICBUS_CALLBACK(device_get_parent(bus),
+		    IIC_REQUEST_BUS, (caddr_t)&how);
+		IICBUS_LOCK(sc);
 
-			IICBUS_UNLOCK(sc);
-			return (0);
+		if (error != 0) {
+			sc->owner = NULL;
+			wakeup_one(sc);
 		}
-
-		/* free any allocated resource */
-		if (error)
-			IICBUS_CALLBACK(device_get_parent(bus), IIC_RELEASE_BUS,
-					(caddr_t)&how);
 	}
+
+
 	IICBUS_UNLOCK(sc);
 
 	return (error);
@@ -131,12 +131,6 @@ iicbus_release_bus(device_t bus, device_t dev)
 	struct iicbus_softc *sc = (struct iicbus_softc *)device_get_softc(bus);
 	int error;
 
-	/* first, ask the underlying layers if the release is ok */
-	error = IICBUS_CALLBACK(device_get_parent(bus), IIC_RELEASE_BUS, NULL);
-
-	if (error)
-		return (error);
-
 	IICBUS_LOCK(sc);
 
 	if (sc->owner != dev) {
@@ -144,13 +138,26 @@ iicbus_release_bus(device_t bus, device_t dev)
 		return (EACCES);
 	}
 
-	sc->owner = NULL;
-
-	/* wakeup waiting processes */
-	wakeup(sc);
+	/* 
+	 * Drop the lock around the call to the bus driver. 
+	 * This call should be allowed to sleep in the IIC_WAIT case.
+	 * Drivers might also need to grab locks that would cause LOR
+	 * if our lock is held.
+	 */
 	IICBUS_UNLOCK(sc);
+	/* Ask the underlying layers if the release is ok */
+	error = IICBUS_CALLBACK(device_get_parent(bus), IIC_RELEASE_BUS, NULL);
 
-	return (0);
+	if (error == 0) {
+		IICBUS_LOCK(sc);
+		sc->owner = NULL;
+
+		/* wakeup a waiting thread */
+		wakeup_one(sc);
+		IICBUS_UNLOCK(sc);
+	}
+
+	return (error);
 }
 
 /*