s390/cio: introduce driver_override on the css bus

Sometimes, we want to control which of the matching drivers
binds to a subchannel device (e.g. for subchannels we want to
handle via vfio-ccw).

For pci devices, a mechanism to do so has been introduced in
782a985d7af2 ("PCI: Introduce new device binding path using
pci_dev.driver_override"). It makes sense to introduce the
driver_override attribute for subchannel devices as well, so
that we can easily extend the 'driverctl' tool (which makes
use of the driver_override attribute for pci).

Note that unlike pci we still require a driver override to
match the subchannel type; matching more than one subchannel
type is probably not useful anyway.

Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

2 files changed, 54 insertions, 0 deletions

diff --git a/drivers/s390/cio/cio.h b/drivers/s390/cio/cio.h
index 4d6c7d16416e..ba7d2480613b 100644
--- a/drivers/s390/cio/cio.h
+++ b/drivers/s390/cio/cio.h
@@ -113,6 +113,7 @@ struct subchannel {
 	enum sch_todo todo;
 	struct work_struct todo_work;
 	struct schib_config config;
+	char *driver_override; /* Driver name to force a match */
 } __attribute__ ((aligned(8)));
 
 DECLARE_PER_CPU_ALIGNED(struct irb, cio_irb);
diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index 7159933d9d3e..e1f2d0eed544 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -167,6 +167,7 @@ static void css_subchannel_release(struct device *dev)
 
 	sch->config.intparm = 0;
 	cio_commit_config(sch);
+	kfree(sch->driver_override);
 	kfree(sch->lock);
 	kfree(sch);
 }
@@ -323,9 +324,57 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
 
 static DEVICE_ATTR_RO(modalias);
 
+static ssize_t driver_override_store(struct device *dev,
+				     struct device_attribute *attr,
+				     const char *buf, size_t count)
+{
+	struct subchannel *sch = to_subchannel(dev);
+	char *driver_override, *old, *cp;
+
+	/* We need to keep extra room for a newline */
+	if (count >= (PAGE_SIZE - 1))
+		return -EINVAL;
+
+	driver_override = kstrndup(buf, count, GFP_KERNEL);
+	if (!driver_override)
+		return -ENOMEM;
+
+	cp = strchr(driver_override, '\n');
+	if (cp)
+		*cp = '\0';
+
+	device_lock(dev);
+	old = sch->driver_override;
+	if (strlen(driver_override)) {
+		sch->driver_override = driver_override;
+	} else {
+		kfree(driver_override);
+		sch->driver_override = NULL;
+	}
+	device_unlock(dev);
+
+	kfree(old);
+
+	return count;
+}
+
+static ssize_t driver_override_show(struct device *dev,
+				    struct device_attribute *attr, char *buf)
+{
+	struct subchannel *sch = to_subchannel(dev);
+	ssize_t len;
+
+	device_lock(dev);
+	len = snprintf(buf, PAGE_SIZE, "%s\n", sch->driver_override);
+	device_unlock(dev);
+	return len;
+}
+static DEVICE_ATTR_RW(driver_override);
+
 static struct attribute *subch_attrs[] = {
 	&dev_attr_type.attr,
 	&dev_attr_modalias.attr,
+	&dev_attr_driver_override.attr,
 	NULL,
 };
 
@@ -1348,6 +1397,10 @@ static int css_bus_match(struct device *dev, struct device_driver *drv)
 	struct css_driver *driver = to_cssdriver(drv);
 	struct css_device_id *id;
 
+	/* When driver_override is set, only bind to the matching driver */
+	if (sch->driver_override && strcmp(sch->driver_override, drv->name))
+		return 0;
+
 	for (id = driver->subchannel_type; id->match_flags; id++) {
 		if (sch->st == id->type)
 			return 1;