HID: uhid: report to user-space whether reports are numbered

This makes UHID_START include a "dev_flags" field that describes details
of the hid-device in the kernel. The first flags we introduce describe
whether a given report-type uses numbered reports. This is useful for
transport layers that force report-numbers and therefore might have to
prefix kernel-provided HID-messages with the report-number.

Currently, only HoG needs this and the spec only talks about "global
report numbers". That is, it's a global boolean not a per-type boolean.
However, given the quirks we already have in kernel-space, a per-type
value seems much more appropriate.
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/uhid.c

@@ -92,8 +92,27 @@ static int uhid_queue_event(struct uhid_device *uhid, __u32 event)
 static int uhid_hid_start(struct hid_device *hid)
 {
 	struct uhid_device *uhid = hid->driver_data;
+	struct uhid_event *ev;
+	unsigned long flags;
+
+	ev = kzalloc(sizeof(*ev), GFP_KERNEL);
+	if (!ev)
+		return -ENOMEM;
+
+	ev->type = UHID_START;
 
-	return uhid_queue_event(uhid, UHID_START);
+	if (hid->report_enum[HID_FEATURE_REPORT].numbered)
+		ev->u.start.dev_flags |= UHID_DEV_NUMBERED_FEATURE_REPORTS;
+	if (hid->report_enum[HID_OUTPUT_REPORT].numbered)
+		ev->u.start.dev_flags |= UHID_DEV_NUMBERED_OUTPUT_REPORTS;
+	if (hid->report_enum[HID_INPUT_REPORT].numbered)
+		ev->u.start.dev_flags |= UHID_DEV_NUMBERED_INPUT_REPORTS;
+
+	spin_lock_irqsave(&uhid->qlock, flags);
+	uhid_queue(uhid, ev);
+	spin_unlock_irqrestore(&uhid->qlock, flags);
+
+	return 0;
 }
 
 static void uhid_hid_stop(struct hid_device *hid)

include/uapi/linux/uhid.h

@@ -54,6 +54,16 @@ struct uhid_create2_req {
 	__u8 rd_data[HID_MAX_DESCRIPTOR_SIZE];
 } __attribute__((__packed__));
 
+enum uhid_dev_flag {
+	UHID_DEV_NUMBERED_FEATURE_REPORTS			= (1ULL << 0),
+	UHID_DEV_NUMBERED_OUTPUT_REPORTS			= (1ULL << 1),
+	UHID_DEV_NUMBERED_INPUT_REPORTS				= (1ULL << 2),
+};
+
+struct uhid_start_req {
+	__u64 dev_flags;
+};
+
 #define UHID_DATA_MAX 4096
 
 enum uhid_report_type {
@@ -182,6 +192,7 @@ struct uhid_event {
 		struct uhid_input2_req input2;
 		struct uhid_set_report_req set_report;
 		struct uhid_set_report_reply_req set_report_reply;
+		struct uhid_start_req start;
 	} u;
 } __attribute__((__packed__));