HID: usbhid: extend the polling interval configuration to keyboards

For mouse and joystick devices user can change the polling interval
via usbhid.mousepoll and usbhid.jspoll.
Implement the same thing for keyboards, so user can
reduce(or increase) input latency this way.

This has been tested with a Cooler Master Devastator with
kbpoll=32, resulting in delay between events of 32 ms(values were taken
from evtest).

Signed-off-by: Filip Alac <filipalac@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/admin-guide/kernel-parameters.txt

@@ -4352,6 +4352,9 @@
 	usbhid.jspoll=
 			[USBHID] The interval which joysticks are to be polled at.
 
+	usbhid.kbpoll=
+			[USBHID] The interval which keyboards are to be polled at.
+
 	usb-storage.delay_use=
 			[UMS] The delay in seconds before a new device is
 			scanned for Logical Units (default 1).

drivers/hid/usbhid/hid-core.c

@@ -56,6 +56,10 @@ static unsigned int hid_jspoll_interval;
 module_param_named(jspoll, hid_jspoll_interval, uint, 0644);
 MODULE_PARM_DESC(jspoll, "Polling interval of joysticks");
 
+static unsigned int hid_kbpoll_interval;
+module_param_named(kbpoll, hid_kbpoll_interval, uint, 0644);
+MODULE_PARM_DESC(kbpoll, "Polling interval of keyboards");
+
 static unsigned int ignoreled;
 module_param_named(ignoreled, ignoreled, uint, 0644);
 MODULE_PARM_DESC(ignoreled, "Autosuspend with active leds");
@@ -1094,7 +1098,9 @@ static int usbhid_start(struct hid_device *hid)
 				hid->name, endpoint->bInterval, interval);
 		}
 
-		/* Change the polling interval of mice and joysticks. */
+		/* Change the polling interval of mice, joysticks
+		 * and keyboards.
+		 */
 		switch (hid->collection->usage) {
 		case HID_GD_MOUSE:
 			if (hid_mousepoll_interval > 0)
@@ -1104,6 +1110,10 @@ static int usbhid_start(struct hid_device *hid)
 			if (hid_jspoll_interval > 0)
 				interval = hid_jspoll_interval;
 			break;
+		case HID_GD_KEYBOARD:
+			if (hid_kbpoll_interval > 0)
+				interval = hid_kbpoll_interval;
+			break;
 		}
 
 		ret = -ENOMEM;