Input: joystick - use ktime for measuring timing

The current codes in gameport and analog joystick drivers for the time
accounting have a long-standing problem when the system is running
with CPU freq; since the timing is measured via TSC or sample counter,
the calculation isn't reliable.

In this patch, as a simple fix, use the standard ktime to measure the
timing.  In case where no high resolution timer is available,
use_ktime bool option is provided to both modules.  Setting
use_ktime=false switches to the old methods.

Tested-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

1 files changed, 40 insertions, 1 deletions

diff --git a/drivers/input/gameport/gameport.c b/drivers/input/gameport/gameport.c
index 24c41ba7d4e0..e29c04e2aff4 100644
--- a/drivers/input/gameport/gameport.c
+++ b/drivers/input/gameport/gameport.c
@@ -23,6 +23,7 @@
 #include <linux/workqueue.h>
 #include <linux/sched.h>	/* HZ */
 #include <linux/mutex.h>
+#include <linux/timekeeping.h>
 
 /*#include <asm/io.h>*/
 
@@ -30,6 +31,10 @@ MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
 MODULE_DESCRIPTION("Generic gameport layer");
 MODULE_LICENSE("GPL");
 
+static bool use_ktime = true;
+module_param(use_ktime, bool, 0400);
+MODULE_PARM_DESC(use_ktime, "Use ktime for measuring I/O speed");
+
 /*
  * gameport_mutex protects entire gameport subsystem and is taken
  * every time gameport port or driver registrered or unregistered.
@@ -76,6 +81,38 @@ static unsigned int get_time_pit(void)
 
 static int gameport_measure_speed(struct gameport *gameport)
 {
+	unsigned int i, t, tx;
+	u64 t1, t2, t3;
+	unsigned long flags;
+
+	if (gameport_open(gameport, NULL, GAMEPORT_MODE_RAW))
+		return 0;
+
+	tx = ~0;
+
+	for (i = 0; i < 50; i++) {
+		local_irq_save(flags);
+		t1 = ktime_get_ns();
+		for (t = 0; t < 50; t++)
+			gameport_read(gameport);
+		t2 = ktime_get_ns();
+		t3 = ktime_get_ns();
+		local_irq_restore(flags);
+		udelay(i * 10);
+		t = (t2 - t1) - (t3 - t2);
+		if (t < tx)
+			tx = t;
+	}
+
+	gameport_close(gameport);
+	t = 1000000 * 50;
+	if (tx)
+		t /= tx;
+	return t;
+}
+
+static int old_gameport_measure_speed(struct gameport *gameport)
+{
 #if defined(__i386__)
 
 	unsigned int i, t, t1, t2, t3, tx;
@@ -521,7 +558,9 @@ static void gameport_add_port(struct gameport *gameport)
 	if (gameport->parent)
 		gameport->parent->child = gameport;
 
-	gameport->speed = gameport_measure_speed(gameport);
+	gameport->speed = use_ktime ?
+		gameport_measure_speed(gameport) :
+		old_gameport_measure_speed(gameport);
 
 	list_add_tail(&gameport->node, &gameport_list);