[PATCH v4 2/7] staging: fsl_-mc: add device binding path 'driver_override'

["J. German Rivera" <German.Rivera@freescale.com>]

From: Bharat Bhushan <bharat.bhushan@freescale.com>

This patch is required for vfio-fsl-mc meta driver to successfully bind
layerscape container devices for device passthrough. This patch adds
a mechanism to allow a layerscape device to specify a driver rather than
a layerscape driver provide a device match.

This patch is based on following proposed patches for PCI and platform devices
- https://lkml.org/lkml/2014/4/8/571  :- For Platform devices
- http://lists-archives.com/linux-kernel/28030441-pci-introduce-new-device-binding-path-using-pci_dev-driver_override.html  :- For PCI devices

Example to allow a device (dprc.1) to specifically bind
with driver (vfio-fsl-mc):-
- echo vfio-fsl-mc > /sys/bus/fsl-mc/devices/dprc.1/driver_override
- echo dprc.1 > /sys/bus/fsl-mc/drivers/fsl_mc_dprc/unbind
- echo dprc.1 > /sys/bus/fsl-mc/drivers/vfio-fsl-mc/bind

Signed-off-by: J. German Rivera <German.Rivera@freescale.com>
Reviewed-by: Stuart Yoder <stuart.yoder@freescale.com>
Tested-by: Stuart Yoder <stuart.yoder@freescale.com>
---
 drivers/staging/fsl-mc/bus/mc-bus.c | 67 +++++++++++++++++++++++++++++++++++++
 drivers/staging/fsl-mc/include/mc.h |  2 ++
 2 files changed, 69 insertions(+)

diff --git a/drivers/staging/fsl-mc/bus/mc-bus.c b/drivers/staging/fsl-mc/bus/mc-bus.c
index 9d98828..fdd3d17 100644
--- a/drivers/staging/fsl-mc/bus/mc-bus.c
+++ b/drivers/staging/fsl-mc/bus/mc-bus.c
@@ -58,6 +58,12 @@ static int fsl_mc_bus_match(struct device *dev, struct device_driver *drv)
 	if (WARN_ON(!fsl_mc_bus_type.dev_root))
 		goto out;

+	/* When driver_override is set, only bind to the matching driver */
+	if (mc_dev->driver_override) {
+		found = !strcmp(mc_dev->driver_override, mc_drv->driver.name);
+		goto out;
+	}
+
 	if (!mc_drv->match_id_table)
 		goto out;

@@ -116,10 +122,69 @@ static int fsl_mc_bus_uevent(struct device *dev, struct kobj_uevent_env *env)
 	return 0;
 }

+static ssize_t driver_override_store(struct device *dev,
+				     struct device_attribute *attr,
+				     const char *buf, size_t count)
+{
+	struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
+	const char *driver_override, *old = mc_dev->driver_override;
+	char *cp;
+
+	if (WARN_ON(dev->bus != &fsl_mc_bus_type))
+		return -EINVAL;
+
+	if (count > PATH_MAX)
+		return -EINVAL;
+
+	driver_override = kstrndup(buf, count, GFP_KERNEL);
+	if (!driver_override)
+		return -ENOMEM;
+
+	cp = strchr(driver_override, '\n');
+	if (cp)
+		*cp = '\0';
+
+	if (strlen(driver_override)) {
+		mc_dev->driver_override = driver_override;
+	} else {
+		kfree(driver_override);
+		mc_dev->driver_override = NULL;
+	}
+
+	kfree(old);
+
+	return count;
+}
+
+static ssize_t driver_override_show(struct device *dev,
+				    struct device_attribute *attr, char *buf)
+{
+	struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
+
+	return sprintf(buf, "%s\n", mc_dev->driver_override);
+}
+
+static DEVICE_ATTR_RW(driver_override);
+
+static struct attribute *fsl_mc_dev_attrs[] = {
+	&dev_attr_driver_override.attr,
+	NULL,
+};
+
+static const struct attribute_group fsl_mc_dev_group = {
+	.attrs = fsl_mc_dev_attrs,
+};
+
+static const struct attribute_group *fsl_mc_dev_groups[] = {
+	&fsl_mc_dev_group,
+	NULL,
+};
+
 struct bus_type fsl_mc_bus_type = {
 	.name = "fsl-mc",
 	.match = fsl_mc_bus_match,
 	.uevent = fsl_mc_bus_uevent,
+	.dev_groups = fsl_mc_dev_groups,
 };
 EXPORT_SYMBOL_GPL(fsl_mc_bus_type);

@@ -492,6 +557,8 @@ void fsl_mc_device_remove(struct fsl_mc_device *mc_dev)
 			fsl_mc_bus_type.dev_root = NULL;
 	}

+	kfree(mc_dev->driver_override);
+	mc_dev->driver_override = NULL;
 	if (!mc_bus)
 		kmem_cache_free(mc_dev_cache, mc_dev);
 	else
diff --git a/drivers/staging/fsl-mc/include/mc.h b/drivers/staging/fsl-mc/include/mc.h
index c543a84..322b594 100644
--- a/drivers/staging/fsl-mc/include/mc.h
+++ b/drivers/staging/fsl-mc/include/mc.h
@@ -145,6 +145,7 @@ struct fsl_mc_device_irq {
  * @regions: pointer to array of MMIO region entries
  * @irqs: pointer to array of pointers to interrupts allocated to this device
  * @resource: generic resource associated with this MC object device, if any.
+ * @driver_override: Driver name to force a match
  *
  * Generic device object for MC object devices that are "attached" to a
  * MC bus.
@@ -177,6 +178,7 @@ struct fsl_mc_device {
 	struct resource *regions;
 	struct fsl_mc_device_irq **irqs;
 	struct fsl_mc_resource *resource;
+	const char *driver_override;
 };

 #define to_fsl_mc_device(_dev) \
--
2.3.3