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drm/nouveau/fan: rewrite the fan tachometer driver to get more precision, faster

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The previous driver waited for 250ms to accumulate data. This version times a
complete fan rotation and extrapolates to RPM.

The fan rotational speed should now be read in less than 250ms (worst case)
and usually in less 50ms.

Signed-off-by: Martin Peres <martin.peres@labri.fr>
Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
This commit is contained in:
Martin Peres 2012-09-02 03:20:45 +02:00 committed by Ben Skeggs
parent aa1b9b4836
commit bf6546b421
1 changed files with 15 additions and 8 deletions
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23
drivers/gpu/drm/nouveau/core/subdev/therm/fan.c
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@ -105,30 +105,37 @@ nouveau_therm_fan_sense(struct nouveau_therm *therm)
struct nouveau_gpio *gpio = nouveau_gpio(therm);
struct dcb_gpio_func func;
u32 cycles, cur, prev;
u64 start;
u64 start, end, tach;
if (gpio->find(gpio, 0, DCB_GPIO_FAN_SENSE, 0xff, &func))
return -ENODEV;
/* Monitor the GPIO input 0x3b for 250ms.
/* Time a complete rotation and extrapolate to RPM:
* When the fan spins, it changes the value of GPIO FAN_SENSE.
* We get 4 changes (0 -> 1 -> 0 -> 1 -> [...]) per complete rotation.
* We get 4 changes (0 -> 1 -> 0 -> 1) per complete rotation.
*/
start = ptimer->read(ptimer);
prev = gpio->get(gpio, 0, func.func, func.line);
cycles = 0;
do {
usleep_range(500, 1000); /* supports 0 < rpm < 7500 */
cur = gpio->get(gpio, 0, func.func, func.line);
if (prev != cur) {
if (!start)
start = ptimer->read(ptimer);
cycles++;
prev = cur;
}
} while (cycles < 5 && ptimer->read(ptimer) - start < 250000000);
end = ptimer->read(ptimer);
usleep_range(500, 1000); /* supports 0 < rpm < 7500 */
} while (ptimer->read(ptimer) - start < 250000000);
/* interpolate to get rpm */
return cycles / 4 * 4 * 60;
if (cycles == 5) {
tach = (u64)60000000000;
do_div(tach, (end - start));
return tach;
} else
return 0;
}
static void