HID: Add HID Report Descriptor to sysfs

Add a new binary sysfs entry called report_descriptor which contains
the HID report descriptor.
Signed-off-by: Alan Ott <alan@signal11.us>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/ABI/testing/sysfs-driver-hid

+What:		For USB devices	: /sys/bus/usb/devices/<busnum>-<devnum>:<config num>.<interface num>/<hid-bus>:<vendor-id>:<product-id>.<num>/report_descriptor
+		For BT devices	: /sys/class/bluetooth/hci<addr>/<hid-bus>:<vendor-id>:<product-id>.<num>/report_descriptor
+		Symlink		: /sys/class/hidraw/hidraw<num>/device/report_descriptor
+Date:		Jan 2011
+KernelVersion:	2.0.39
+Contact:	Alan Ott <alan@signal11.us>
+Description:	When read, this file returns the device's raw binary HID
+		report descriptor.
+		This file cannot be written.
+Users:		HIDAPI library (http://www.signal11.us/oss/hidapi)

drivers/hid/hid-core.c

@@ -1159,6 +1159,32 @@ static bool hid_hiddev(struct hid_device *hdev)
 	return !!hid_match_id(hdev, hid_hiddev_list);
 }
 
+
+static ssize_t
+read_report_descriptor(struct file *filp, struct kobject *kobj,
+		struct bin_attribute *attr,
+		char *buf, loff_t off, size_t count)
+{
+	struct device *dev = container_of(kobj, struct device, kobj);
+	struct hid_device *hdev = container_of(dev, struct hid_device, dev);
+
+	if (off >= hdev->rsize)
+		return 0;
+
+	if (off + count > hdev->rsize)
+		count = hdev->rsize - off;
+
+	memcpy(buf, hdev->rdesc + off, count);
+
+	return count;
+}
+
+static struct bin_attribute dev_bin_attr_report_desc = {
+	.attr = { .name = "report_descriptor", .mode = 0444 },
+	.read = read_report_descriptor,
+	.size = HID_MAX_DESCRIPTOR_SIZE,
+};
+
 int hid_connect(struct hid_device *hdev, unsigned int connect_mask)
 {
 	static const char *types[] = { "Device", "Pointer", "Mouse", "Device",
@@ -1169,6 +1195,7 @@ int hid_connect(struct hid_device *hdev, unsigned int connect_mask)
 	char buf[64];
 	unsigned int i;
 	int len;
+	int ret;
 
 	if (hdev->quirks & HID_QUIRK_HIDDEV_FORCE)
 		connect_mask |= (HID_CONNECT_HIDDEV_FORCE | HID_CONNECT_HIDDEV);
@@ -1230,6 +1257,11 @@ int hid_connect(struct hid_device *hdev, unsigned int connect_mask)
 		bus = "<UNKNOWN>";
 	}
 
+	ret = device_create_bin_file(&hdev->dev, &dev_bin_attr_report_desc);
+	if (ret)
+		hid_warn(hdev,
+			 "can't create sysfs report descriptor attribute err: %d\n", ret);
+
 	hid_info(hdev, "%s: %s HID v%x.%02x %s [%s] on %s\n",
 		 buf, bus, hdev->version >> 8, hdev->version & 0xff,
 		 type, hdev->name, hdev->phys);
@@ -1240,6 +1272,7 @@ EXPORT_SYMBOL_GPL(hid_connect);
 
 void hid_disconnect(struct hid_device *hdev)
 {
+	device_remove_bin_file(&hdev->dev, &dev_bin_attr_report_desc);
 	if (hdev->claimed & HID_CLAIMED_INPUT)
 		hidinput_disconnect(hdev);
 	if (hdev->claimed & HID_CLAIMED_HIDDEV)