[PATCH v2] HID: rmi: Scan the report descriptor to determine if the device is suitable for the hid-rmi driver

[Andrew Duggan <aduggan@synaptics.com>]

On composite HID devices there may be multiple HID devices on separate interfaces, but hid-rmi
should only bind to the touchpad. The previous version simply checked that the interface protocol
was set to mouse. Unfortuately, it is not always the case that the touchpad has the mouse interface
protocol set. This patch takes a different approach and scans the report descriptor looking for
the Generic Desktop Pointer usage and the Vendor Specific Top Level Collection needed by the
hid-rmi driver to interface with the device.

Signed-off-by: Andrew Duggan <aduggan@synaptics.com>
---
This is a second attempt at the patch I submitted back in October. Instead of looking for specific
HID reports this patch looks for the Generic Desktop Pointer usage. Having that usage along with
the vendor specific collection seems to be a distinctive enough to id the Synaptics touchpad in
the composite USB device.

 drivers/hid/hid-core.c | 21 ++++++++++++++++-----
 include/linux/hid.h    |  4 +++-
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 12b6e67..ba9dc59 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -698,10 +698,20 @@ static void hid_scan_feature_usage(struct hid_parser *parser, u32 usage)
 static void hid_scan_collection(struct hid_parser *parser, unsigned type)
 {
 	struct hid_device *hid = parser->device;
+	int i;
 
 	if (((parser->global.usage_page << 16) == HID_UP_SENSOR) &&
 	    type == HID_COLLECTION_PHYSICAL)
 		hid->group = HID_GROUP_SENSOR_HUB;
+
+	if ((parser->global.usage_page << 16) == HID_UP_GENDESK)
+		for (i = 0; i < parser->local.usage_index; i++)
+			if (parser->local.usage[i] == HID_GD_POINTER)
+				parser->scan_flags
+					|= HID_SCAN_FLAG_GENDESK_POINTER;
+
+	if ((parser->global.usage_page << 16) == HID_UP_MSVENDOR)
+		parser->scan_flags |= HID_SCAN_FLAG_VENDOR_SPECIFIC;
 }
 
 static int hid_scan_main(struct hid_parser *parser, struct hid_item *item)
@@ -783,11 +793,12 @@ static int hid_scan_report(struct hid_device *hid)
 	* Vendor specific handlings
 	*/
 	if ((hid->vendor == USB_VENDOR_ID_SYNAPTICS) &&
-	    (hid->group == HID_GROUP_GENERIC) &&
-	    /* only bind to the mouse interface of composite USB devices */
-	    (hid->bus != BUS_USB || hid->type == HID_TYPE_USBMOUSE))
-		/* hid-rmi should take care of them, not hid-generic */
-		hid->group = HID_GROUP_RMI;
+	    (hid->group == HID_GROUP_GENERIC)) {
+		if ((parser->scan_flags & HID_SCAN_FLAG_VENDOR_SPECIFIC)
+		    && (parser->scan_flags & HID_SCAN_FLAG_GENDESK_POINTER))
+			/* hid-rmi should take care of them, not hid-generic */
+			hid->group = HID_GROUP_RMI;
+	}
 
 	/*
 	 * Vendor specific handlings
diff --git a/include/linux/hid.h b/include/linux/hid.h
index f53c4a9..b019f15 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -547,7 +547,9 @@ static inline void hid_set_drvdata(struct hid_device *hdev, void *data)
 #define HID_GLOBAL_STACK_SIZE 4
 #define HID_COLLECTION_STACK_SIZE 4
 
-#define HID_SCAN_FLAG_MT_WIN_8			0x00000001
+#define HID_SCAN_FLAG_MT_WIN_8			BIT(0)
+#define HID_SCAN_FLAG_VENDOR_SPECIFIC		BIT(1)
+#define HID_SCAN_FLAG_GENDESK_POINTER		BIT(2)
 
 struct hid_parser {
 	struct hid_global     global;
-- 
2.1.0