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Date: Thu, 21 Aug 2014 13:29:03 +0200
From: Takashi Iwai <tiwai@...e.de>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Andreas Mohr <andi@...as.de>, linux-input@...r.kernel.org,
linux-kernel@...r.kernel.org, Vojtech Pavlik <vojtech@...e.cz>,
Jiri Kosina <jkosina@...e.cz>
Subject: Re: [PATCH 1/2] SOUND: kill gameport bits
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@...e.de>
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@...e.de>
---
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@....cz>");
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@....cz>");
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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