[RFC 4/5] hid: Add idtags to modalias

["Henrik Rydberg" <rydberg@euromail.se>]

HID devices are only partially presented to userland.  Hotplugged
devices emit events containing a modalias based on the basic bus,
vendor and product entities. However, in practise a hid device can
depend on details such as a single usb interface or a particular item
in a report descriptor.

This patch adds a special interface tag to the hid device id, and
broadcasts it using both uevent and modalias. Matching ids are
introduced for the hid-multitouch driver. As a consequence, generic
hid will no longer match multitouch devices, and udev will
automatically load hid-multitouch instead.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
---
 drivers/hid/hid-core.c          |   28 +++++++++++++++++++++++++---
 drivers/hid/hid-multitouch.c    |    7 ++++++-
 include/linux/hid.h             |    7 +++++++
 include/linux/mod_devicetable.h |    2 +-
 scripts/mod/file2alias.c        |    2 ++
 5 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 8a7b59e..1cf6cb5 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -205,6 +205,10 @@ static int hid_add_usage(struct hid_parser *parser, unsigned usage)
 		parser->collection_stack_ptr ?
 		parser->collection_stack[parser->collection_stack_ptr - 1] : 0;
 	parser->local.usage_index++;
+
+	if (usage == HID_DG_CONTACTID)
+		parser->device->idtags |= HID_IDTAG_MULTITOUCH;
+
 	return 0;
 }
 
@@ -1154,7 +1158,7 @@ EXPORT_SYMBOL_GPL(hid_input_report);
 static bool hid_match_one_id(struct hid_device *hdev,
 		const struct hid_device_id *id)
 {
-	return id->bus == hdev->bus &&
+	return id->bus == hdev->bus && id->idtags == hdev->idtags &&
 		(id->vendor == HID_ANY_ID || id->vendor == hdev->vendor) &&
 		(id->product == HID_ANY_ID || id->product == hdev->product);
 }
@@ -1723,6 +1727,23 @@ static int hid_device_remove(struct device *dev)
 	return 0;
 }
 
+static ssize_t modalias_show(struct device *dev, struct device_attribute *a,
+			     char *buf)
+{
+	struct hid_device *hdev = container_of(dev, struct hid_device, dev);
+	int len;
+
+	len = snprintf(buf, PAGE_SIZE, "hid:b%04Xi%04Xv%08Xp%08X\n",
+		       hdev->bus, hdev->idtags, hdev->vendor, hdev->product);
+
+	return (len >= PAGE_SIZE) ? (PAGE_SIZE - 1) : len;
+}
+
+static struct device_attribute hid_dev_attrs[] = {
+	__ATTR_RO(modalias),
+	__ATTR_NULL,
+};
+
 static int hid_uevent(struct device *dev, struct kobj_uevent_env *env)
 {
 	struct hid_device *hdev = container_of(dev, struct hid_device, dev);
@@ -1740,8 +1761,8 @@ static int hid_uevent(struct device *dev, struct kobj_uevent_env *env)
 	if (add_uevent_var(env, "HID_UNIQ=%s", hdev->uniq))
 		return -ENOMEM;
 
-	if (add_uevent_var(env, "MODALIAS=hid:b%04Xv%08Xp%08X",
-			hdev->bus, hdev->vendor, hdev->product))
+	if (add_uevent_var(env, "MODALIAS=hid:b%04Xi%04Xv%08Xp%08X",
+			   hdev->bus, hdev->idtags, hdev->vendor, hdev->product))
 		return -ENOMEM;
 
 	return 0;
@@ -1749,6 +1770,7 @@ static int hid_uevent(struct device *dev, struct kobj_uevent_env *env)
 
 static struct bus_type hid_bus_type = {
 	.name		= "hid",
+	.dev_attrs	= hid_dev_attrs,
 	.match		= hid_bus_match,
 	.probe		= hid_device_probe,
 	.remove		= hid_device_remove,
diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
index 421b16c..80ceab5 100644
--- a/drivers/hid/hid-multitouch.c
+++ b/drivers/hid/hid-multitouch.c
@@ -104,7 +104,7 @@ struct mt_device {
 #define MT_DEFAULT_MAXCONTACT	10
 
 #define HID_USB_MT_DEVICE(v, p)						\
-	HID_USB_DEVICE(v, p)
+	.idtags = HID_IDTAG_MULTITOUCH, HID_USB_DEVICE(v, p)
 
 /*
  * these device-dependent functions determine what slot corresponds
@@ -886,6 +886,11 @@ static const struct hid_device_id mt_devices[] = {
 		HID_USB_MT_DEVICE(USB_VENDOR_ID_XIROKU,
 			USB_DEVICE_ID_XIROKU_CSR2) },
 
+	/* Generic MT device */
+	{ .driver_data = MT_CLS_DEFAULT,
+		HID_USB_MT_DEVICE(HID_ANY_ID,
+			HID_ANY_ID) },
+
 	{ }
 };
 MODULE_DEVICE_TABLE(hid, mt_devices);
diff --git a/include/linux/hid.h b/include/linux/hid.h
index 5b3be43..1e68543 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -62,6 +62,12 @@
 
 #define HID_MAX_DESCRIPTOR_SIZE		4096
 
+/*
+ * HID identifying tags extracted from reports
+ */
+#define HID_IDTAG_MULTITOUCH		0x0001
+
+
 #ifdef __KERNEL__
 
 #include <linux/types.h>
@@ -473,6 +479,7 @@ struct hid_device {							/* device report descriptor */
 	unsigned maxcollection;						/* Number of parsed collections */
 	unsigned maxapplication;					/* Number of applications */
 	__u16 bus;							/* BUS ID */
+	__u16 idtags;							/* Identifying tags extracted from reports */
 	__u32 vendor;							/* Vendor ID */
 	__u32 product;							/* Product ID */
 	__u32 version;							/* HID version */
diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index 83ac071..25446f0 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -135,7 +135,7 @@ struct usb_device_id {
 
 struct hid_device_id {
 	__u16 bus;
-	__u16 pad1;
+	__u16 idtags;
 	__u32 vendor;
 	__u32 product;
 	kernel_ulong_t driver_data
diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
index b89efe6..d0c3a2b 100644
--- a/scripts/mod/file2alias.c
+++ b/scripts/mod/file2alias.c
@@ -336,10 +336,12 @@ static int do_hid_entry(const char *filename,
 			     struct hid_device_id *id, char *alias)
 {
 	id->bus = TO_NATIVE(id->bus);
+	id->idtags = TO_NATIVE(id->idtags);
 	id->vendor = TO_NATIVE(id->vendor);
 	id->product = TO_NATIVE(id->product);
 
 	sprintf(alias, "hid:b%04X", id->bus);
+	ADD(alias, "i", true, id->idtags);
 	ADD(alias, "v", id->vendor != HID_ANY_ID, id->vendor);
 	ADD(alias, "p", id->product != HID_ANY_ID, id->product);
 
-- 
1.7.9.5