From f2991d30ff590bf932483a6dfc16c7ebe2f83341 Mon Sep 17 00:00:00 2001
From: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Date: Fri, 13 Apr 2018 12:42:40 +0300
Subject: [PATCH] bus: fsl-mc: add device binding path 'driver_override'

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: Bharat Bhushan <Bharat.Bhushan@nxp.com>
Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
---
 drivers/bus/fsl-mc/fsl-mc-bus.c | 53 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

--- a/drivers/bus/fsl-mc/fsl-mc-bus.c
+++ b/drivers/bus/fsl-mc/fsl-mc-bus.c
@@ -83,6 +83,12 @@ static int fsl_mc_bus_match(struct devic
 	struct fsl_mc_driver *mc_drv = to_fsl_mc_driver(drv);
 	bool found = false;
 
+	/* 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;
 
@@ -147,8 +153,52 @@ static ssize_t modalias_show(struct devi
 }
 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 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 >= (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';
+
+	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 snprintf(buf, PAGE_SIZE, "%s\n", mc_dev->driver_override);
+}
+static DEVICE_ATTR_RW(driver_override);
+
 static struct attribute *fsl_mc_dev_attrs[] = {
 	&dev_attr_modalias.attr,
+	&dev_attr_driver_override.attr,
 	NULL,
 };
 
@@ -749,6 +799,9 @@ EXPORT_SYMBOL_GPL(fsl_mc_device_add);
  */
 void fsl_mc_device_remove(struct fsl_mc_device *mc_dev)
 {
+	kfree(mc_dev->driver_override);
+	mc_dev->driver_override = NULL;
+
 	/*
 	 * The device-specific remove callback will get invoked by device_del()
 	 */