cdx: add sysfs for bus reset

Add sysfs interface reset to reset all the devices on the CDX bus.

Signed-off-by: Abhijit Gangurde <abhijit.gangurde@amd.com>
Link: https://lore.kernel.org/r/20231017160505.10640-7-abhijit.gangurde@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: abhijitG-xlnx

Documentation/ABI/testing/sysfs-bus-cdx

@@ -45,10 +45,10 @@ What:		/sys/bus/cdx/devices/.../reset
 Date:		March 2023
 Contact:	nipun.gupta@amd.com
 Description:
-		Writing y/1/on to this file resets the CDX device.
-		On resetting the device, the corresponding driver is notified
-		twice, once before the device is being reset, and again after
-		the reset has been complete.
+		Writing y/1/on to this file resets the CDX device or all devices
+		on the bus. On resetting the device, the corresponding driver is
+		notified twice, once before the device is being reset, and again
+		after the reset has been complete.
 
 		For example::
 

drivers/cdx/cdx.c

@@ -110,6 +110,20 @@ int cdx_dev_reset(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(cdx_dev_reset);
 
+/**
+ * reset_cdx_device - Reset a CDX device
+ * @dev: CDX device
+ * @data: This is always passed as NULL, and is not used in this API,
+ *    but is required here as the device_for_each_child() API expects
+ *    the passed function to have this as an argument.
+ *
+ * Return: -errno on failure, 0 on success.
+ */
+static int reset_cdx_device(struct device *dev, void *data)
+{
+	return cdx_dev_reset(dev);
+}
+
 /**
  * cdx_unregister_device - Unregister a CDX device
  * @dev: CDX device
@@ -343,6 +357,7 @@ static DEVICE_ATTR_WO(remove);
 static ssize_t reset_store(struct device *dev, struct device_attribute *attr,
 			   const char *buf, size_t count)
 {
+	struct cdx_device *cdx_dev = to_cdx_device(dev);
 	bool val;
 	int ret;
 
@@ -352,11 +367,13 @@ static ssize_t reset_store(struct device *dev, struct device_attribute *attr,
 	if (!val)
 		return -EINVAL;
 
-	ret = cdx_dev_reset(dev);
-	if (ret)
-		return ret;
+	if (cdx_dev->is_bus)
+		/* Reset all the devices attached to cdx bus */
+		ret = device_for_each_child(dev, NULL, reset_cdx_device);
+	else
+		ret = cdx_dev_reset(dev);
 
-	return count;
+	return ret < 0 ? ret : count;
 }
 static DEVICE_ATTR_WO(reset);
 
@@ -461,6 +478,7 @@ static const struct attribute_group cdx_dev_group = {
 
 static struct attribute *cdx_bus_dev_attrs[] = {
 	&dev_attr_enable.attr,
+	&dev_attr_reset.attr,
 	NULL,
 };