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Commit bf6546b4 authored by Martin Peres's avatar Martin Peres Committed by Ben Skeggs
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drm/nouveau/fan: rewrite the fan tachometer driver to get more precision, faster 



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: default avatarMartin Peres <martin.peres@labri.fr>
Reviewed-by: default avatarBen Skeggs <bskeggs@redhat.com>
Signed-off-by: default avatarBen Skeggs <bskeggs@redhat.com>
parent aa1b9b48

drivers/gpu/drm/nouveau/core/subdev/therm/fan.c

+16 −9
Original line number Diff line number Diff line
@@ -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;

		}



		usleep_range(500, 1000); /* supports 0 < rpm < 7500 */

	} while (ptimer->read(ptimer) - start < 250000000);



	/* interpolate to get rpm */

	return cycles / 4 * 4 * 60;

	} while (cycles < 5 && ptimer->read(ptimer) - start < 250000000);

	end = ptimer->read(ptimer);



	if (cycles == 5) {

		tach = (u64)60000000000;

		do_div(tach, (end - start));

		return tach;

	} else

		return 0;

}



static void