Re: [PATCH 1/2] SOUND: kill gameport bits

[Takashi Iwai]

At Wed, 20 Aug 2014 09:05:58 +0200,
Takashi Iwai wrote:
> 
> > > > > Also, I'm left wondering why e.g. my Athlon XP system (a very popular
> > > > > choice for longer times) would be affected by Cpufreq...
> > > > > And there are no details on how exactly cpufreq is a problem or how this
> > > > > timing issue could be fixed...
> > > > 
> > > > If you take a look at gameport_measure_speed() in gameport.c you will see that
> > > > it counts cycles for timing, which obviously does not work that well when CPU
> > > > frequency changes.
> > > > 
> > > > The bugs have been opened in bugzilla/reported on lists ages ago but nobody
> > > > stepped up to fix that.
> > > 
> > > Hm, can't we just use the standard ktime for measuring the time diff?
> > 
> > We could use high-res timers, if they are available. Are they available on such
> > old hardware and are they sufficiently fast to provide needed timings? I
> > definitely do not have any hardware to est with.
> 
> The boards aren't necessarily bound with the old hardware.  PCI boards
> run fine on the modern machines if they still have a PCI slot (how
> lucky).  And, the highres timer itself isn't so new...

I did a quick hack and it seems working on my box.
The patch is below.


thanks,

Takashi

-- 8< --
From: Takashi Iwai <tiwai@xxxxxxx>
Subject: [PATCH] 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.

Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
 drivers/input/gameport/gameport.c | 38 ++++++++++++++++++++-
 drivers/input/joystick/analog.c   | 70 ++++++++++++++++++++++++++++-----------
 2 files changed, 88 insertions(+), 20 deletions(-)

diff --git a/drivers/input/gameport/gameport.c b/drivers/input/gameport/gameport.c
index 24c41ba7d4e0..48d91f12e397 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 +31,9 @@ MODULE_AUTHOR("Vojtech Pavlik <vojtech@xxxxxx>");
 MODULE_DESCRIPTION("Generic gameport layer");
 MODULE_LICENSE("GPL");
 
+static bool use_ktime = true;
+module_param(use_ktime, bool, 0400);
+
 /*
  * gameport_mutex protects entire gameport subsystem and is taken
  * every time gameport port or driver registrered or unregistered.
@@ -76,6 +80,36 @@ static unsigned int get_time_pit(void)
 
 static int gameport_measure_speed(struct gameport *gameport)
 {
+	unsigned int i, t, tx;
+	u64 t1, t2;
+	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();
+		local_irq_restore(flags);
+		udelay(i * 10);
+		if (t2 - t1 < tx)
+			tx = t2 - t1;
+	}
+
+	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 +555,9 @@ 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);
 
diff --git a/drivers/input/joystick/analog.c b/drivers/input/joystick/analog.c
index ab0fdcd36e18..723276d40b58 100644
--- a/drivers/input/joystick/analog.c
+++ b/drivers/input/joystick/analog.c
@@ -36,6 +36,7 @@
 #include <linux/gameport.h>
 #include <linux/jiffies.h>
 #include <linux/timex.h>
+#include <linux/timekeeping.h>
 
 #define DRIVER_DESC	"Analog joystick and gamepad driver"
 
@@ -43,6 +44,9 @@ MODULE_AUTHOR("Vojtech Pavlik <vojtech@xxxxxx>");
 MODULE_DESCRIPTION(DRIVER_DESC);
 MODULE_LICENSE("GPL");
 
+static bool use_ktime = true;
+module_param(use_ktime, bool, 0400);
+
 /*
  * Option parsing.
  */
@@ -171,6 +175,25 @@ static unsigned long analog_faketime = 0;
 #warning Precise timer not defined for this architecture.
 #endif
 
+static inline u64 get_time(void)
+{
+	if (use_ktime) {
+		return ktime_get_ns();
+	} else {
+		unsigned int x;
+		GET_TIME(x);
+		return x;
+	}
+}
+
+static inline unsigned int delta(u64 x, u64 y)
+{
+	if (use_ktime)
+		return y - x;
+	else
+		return DELTA((unsigned int)x, (unsigned int)y);
+}
+
 /*
  * analog_decode() decodes analog joystick data and reports input events.
  */
@@ -226,7 +249,8 @@ static void analog_decode(struct analog *analog, int *axes, int *initial, int bu
 static int analog_cooked_read(struct analog_port *port)
 {
 	struct gameport *gameport = port->gameport;
-	unsigned int time[4], start, loop, now, loopout, timeout;
+	u64 time[4], start, loop, now;
+	unsigned int loopout, timeout;
 	unsigned char data[4], this, last;
 	unsigned long flags;
 	int i, j;
@@ -236,7 +260,7 @@ static int analog_cooked_read(struct analog_port *port)
 
 	local_irq_save(flags);
 	gameport_trigger(gameport);
-	GET_TIME(now);
+	now = get_time();
 	local_irq_restore(flags);
 
 	start = now;
@@ -249,16 +273,16 @@ static int analog_cooked_read(struct analog_port *port)
 
 		local_irq_disable();
 		this = gameport_read(gameport) & port->mask;
-		GET_TIME(now);
+		now = get_time();
 		local_irq_restore(flags);
 
-		if ((last ^ this) && (DELTA(loop, now) < loopout)) {
+		if ((last ^ this) && (delta(loop, now) < loopout)) {
 			data[i] = last ^ this;
 			time[i] = now;
 			i++;
 		}
 
-	} while (this && (i < 4) && (DELTA(start, now) < timeout));
+	} while (this && (i < 4) && (delta(start, now) < timeout));
 
 	this <<= 4;
 
@@ -266,7 +290,7 @@ static int analog_cooked_read(struct analog_port *port)
 		this |= data[i];
 		for (j = 0; j < 4; j++)
 			if (data[i] & (1 << j))
-				port->axes[j] = (DELTA(start, time[i]) << ANALOG_FUZZ_BITS) / port->loop;
+				port->axes[j] = (delta(start, time[i]) << ANALOG_FUZZ_BITS) / port->loop;
 	}
 
 	return -(this != port->mask);
@@ -365,31 +389,39 @@ static void analog_close(struct input_dev *dev)
 static void analog_calibrate_timer(struct analog_port *port)
 {
 	struct gameport *gameport = port->gameport;
-	unsigned int i, t, tx, t1, t2, t3;
+	unsigned int i, t, tx;
+	u64 t1, t2, t3;
 	unsigned long flags;
 
-	local_irq_save(flags);
-	GET_TIME(t1);
+	if (use_ktime) {
+		port->speed = 1000000;
+	} else {
+		local_irq_save(flags);
+		t1 = get_time();
 #ifdef FAKE_TIME
-	analog_faketime += 830;
+		analog_faketime += 830;
 #endif
-	mdelay(1);
-	GET_TIME(t2);
-	GET_TIME(t3);
-	local_irq_restore(flags);
+		mdelay(1);
+		t2 = get_time();
+		t3 = get_time();
+		local_irq_restore(flags);
 
-	port->speed = DELTA(t1, t2) - DELTA(t2, t3);
+		port->speed = delta(t1, t2) - delta(t2, t3);
+	}
 
 	tx = ~0;
 
 	for (i = 0; i < 50; i++) {
 		local_irq_save(flags);
-		GET_TIME(t1);
-		for (t = 0; t < 50; t++) { gameport_read(gameport); GET_TIME(t2); }
-		GET_TIME(t3);
+		t1 = get_time();
+		for (t = 0; t < 50; t++) {
+			gameport_read(gameport);
+			t2 = get_time();
+		}
+		t3 = get_time();
 		local_irq_restore(flags);
 		udelay(i);
-		t = DELTA(t1, t2) - DELTA(t2, t3);
+		t = delta(t1, t2) - delta(t2, t3);
 		if (t < tx) tx = t;
 	}
 
-- 
2.0.4

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